Codes 41 & 91 With New 02 Sensors

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The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. If you found it cut in some other place, you get to splice it back together. Solder the spice and cover it with head shrink tubing. DO NOT USE CRIMP TERMIALS. The crimped connections are subject to moisture and corrosion.
Bolt the orange wire down to one of the lower intake manifold bolts or to one of the bolts on the back of the cylinder head.

Here are a number of possibilities for a purple wire with no stripe:
PURPLE HEATED WINDSHIELD CONTROL TO EEC AIR COND TERM 585
PURPLE CONVERTIBLE TOP RELAY TO SWITCH 588
PURPLE R.H. REMOTE MIRROR MOTOR FEED-C.C.W. 544
PURPLE HEADLAMP DIMMER SWITCH TO HEADLAMP DIMMER RELAY 500
PURPLE C.B. A+ DIGIT 712
PURPLE RELAY COIL FEED #2 714
PURPLE REDUNDANT MODULE TO ENGINE WARNING LAMP 656
PURPLE POWER FEED FROM AMPLIFIER
PURPLE LEFT CHANNEL SIGNAL 856
PURPLE MODULE TO RELAY 462
PURPLE TRANSMISSION DIAGNOSTIC 453
PURPLE POWER SERVO TO CLIMATE CONTROL UNIT (AMP) 246
PURPLE ELECTRONIC CLUSTER FROM TRIP RECALL SWITCH IN KEYBOARD 288
 
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Awesome! I'll ground the orange wire like you said and see if the codes go away. With all those options on the purple wire I'll have to get out the multimeter.
@dnbonds
I would hold off on that for a while. The orange wire in the picture isn't on the intake manifold, so it may go somewhere else. Go look for the solid color orange wire on the passenger side of the fuel injector harness. That's the one that gets the ground.

Here are the possibilities:

ORANGE WINDSHIELD WIPER SWITCH TO INTERMITTENT GOVERNORGROUND 589
ORANGE HEATED WINDSHIELD SWITCH TO HEATED WINDSHIELD CONTROL 582
ORANGE BRAKE PRESSURE SWITCH TO CONTROL MODULE 636
ORANGE ELECT SHIFT 4 x 4 MODULE TO MOTOR CONTROL 778
ORANGE BRAKE PRESSURE SWITCH TO CONTROL MODULE 636
ORANGE SPEAKER VOICE COIL FEED LEFT FRONT CHANNEL AMP INPUT 649
ORANGE MODULE DIAGNOSTIC 693
ORANGE C.B. C-DIGIT 704
ORANGE MULTIPLEX RELAY COIL FEED 699
ORANGE FUEL CONTROL SWITCH TO FUEL CONTROL VALVE 974
ORANGE BATTERY FEED TO RELAY CONTROLLER 931
ORANGE RIGHT MOTOR-PASSENGER - F 864
ORANGE VALVE #2 TO MODULE 496
ORANGE MEMORY MIRROR MODULE RH HORIZONTAL POSITION 892
ORANGE FUEL SENSOR GROUND TO E.C.U. 89
ORANGE SWITCH OFF TO RELAY 274
ORANGE HEATER & A/C CONTROL SW. (LO-NORM) TO POWER SERVO 250
ORANGE ELECTRONIC CLUSTER FROM EXPANDED FUEL IN KEYBOARD 285
ORANGE 16 GA FUSE LINK 300
ORANGE RELAY TO SEAT LATCH SOLENOID
 
So where can i find a testing o2 sensors thats reliable. Cause im noticing that urs says 43 and 29 are left and right. But further down it says 29 and 43 are left and right.....

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
The computer pins are 29 (LH O2 with a Gray/Lt blue wire) and 43 (RH O2 with a Red/Black wire).

I wonder how many ppl have fried theyre comps because of that mess up. Ive read the same thing on about 100 posts with your diagram on it
 
@Blucifer99

Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. You can expect to see the voltage switch from .2 volt to .6 volt on the average O2 sensor. More voltage swing is good, less voltage swing is bad.
does this clear things up for you?
 
So where can i find a testing o2 sensors thats reliable. Cause im noticing that urs says 43 and 29 are left and right. But further down it says 29 and 43 are left and right.....

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
The computer pins are 29 (LH O2 with a Gray/Lt blue wire) and 43 (RH O2 with a Red/Black wire).

I wonder how many ppl have fried theyre comps because of that mess up. Ive read the same thing on about 100 posts with your diagram on it
You must be using an old version of the test path. The blue text indicates the revision date of the document. I make changes and additions as they are needed. The current version is: Revised 20-July-2017 to add note that the 94-95 uses a 4 wire O2 sensor.

I am a computer and electronics tech by trade with a degree in electronics technology and have been fixing computers and electronic gear for 39+ years.

Measuring voltages will not damage a computer. When voltmeters and multimeters are used to measure voltage, they do not source any current or voltage; they are passive devices. Instruments such as multimeters and voltmeters used to measure voltages have a high input resistance and have a very small current draw, typically measured in microamps. That is by design since drawing any significant amount of current can produce incorrect readings.
 
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@Blucifer99

Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. You can expect to see the voltage switch from .2 volt to .6 volt on the average O2 sensor. More voltage swing is good, less voltage swing is bad.
does this clear things up for you?

No it doesnt clear nothing up LOL cause i own a 92 lx and the wires are grey and light blue with red and black I need to kno which wire is the right and which wire is the left cause i tested my o2s and the passenger side at idle.. starts off low .01v then warms up and goes to about .45v-.50v the drivers side starts up .01v then warms up to .35v then jumps all over inbetween .30v-.90vs and im tryin to figure out a code 92 so the proper diagrams would be greatly appreciated
 
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You must be using an old version of the test path. The blue text indicates the revision date of the document. I make changes and additions as they are needed. The current version is: Revised 20-July-2017 to add note that the 94-95 uses a 4 wire O2 sensor.

I am a computer and electronics tech by trade with a degree in electronics technology and have been fixing computers and electronic gear for 39+ years.

Measuring voltages will not damage a computer. When voltmeters and multimeters are used to measure voltage, they do not source any current or voltage; they are passive devices. Instruments such as multimeters and voltmeters used to measure voltages have a high input resistance and have a very small current draw, typically measured in microamps. That is by design since drawing any significant amount of current can produce incorrect readings.

well i hate to point out the fact that i put up the 91-93 question.... so why show me the 94-95 ??? lol i get your a electronic tec but comon i put up the 91-93 and both of you guys put up the wrong info that i asked for... i must be goin crazy or something lol
 
You have two or more posts for the same probllem
well i hate to point out the fact that i put up the 91-93 question.... so why show me the 94-95 ??? lol i get your a electronic tec but comon i put up the 91-93 and both of you guys put up the wrong info that i asked for... i must be goin crazy or something lol
What's the post number and where is it?

Code 41 or 91. Or 43 Three digit code 172 or 176 - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.

Revised 20-July-2017 to add note that the 94-95 uses a 4 wire O2 sensor.

Code 41 is the passenger side sensor, as viewed from the driver's seat.
Code 91 is the driver side sensor, as viewed from the driver's seat.

Code 172 is the passenger side sensor as viewed from the driver's seat.
Code 176 is the driver side sensor, as viewed from the driver's seat.

Code 43 is not side specific according to the Probst Ford Fuel injection book.

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Testing the O2 sensors 87-93 5.0 Mustangs
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear.

Disconnect the O2 sensor from the harness and use the body side O2 sensor harness as the starting point for testing. Do not measure the resistance of the O2 sensor , you may damage it. Resistance measurements for the O2 sensor harness are made with one meter lead on the O2 sensor harness and the other meter lead on the computer wire or pin for the O2 sensor.

Computer wiring harness connector, computer side.
View attachment 611595
Backside view of the computer wiring connector:
View attachment 611596

87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
The computer pins are 29 (L\RH O2 with a dark green/pink wire) and 43 (LH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
The computer pins are 29 (LH O2 with a Gray/Lt blue wire) and 43 (RH O2 with a Red/Black wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Testing the O2 sensors 94-95 5.0 Mustangs; note that the 94-95 uses a 4 wire O2 sensor.
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a red/black wire) and 27 (RH O2 with a gray/lt blue wire). Use pin 32 (gray/red wire) to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

Testing the O2 sensor wiring harness
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer. Using the Low Ohms range (usually 200 Ohms) you should see less than 1.5 Ohms.

87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Dark blue/Lt green wire in the LH O2 sensor harness and the Dark blue/Lt green wire on the computer pin 43
From the Dark Green/Pink wire on the RH Os sensor harness and the Dark Green/Pink wire on the computer pin 29

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 43
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 29

94-95 5.0 Mustangs:
Computer pin 29 Red/Black – LH O2 sensor
Computer pin 27 Gray/Lt blue – RH O2 sensor
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 29
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 27

There is a connector between the body harness and the O2 sensor harness. Make sure the connectors are mated together, the contacts and wiring are not damaged and the contacts are clean and not coated with oil.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

Check the fuel pressure – the fuel pressure is 37-41 PSI with the vacuum disconnected and the engine idling. Fuel pressure out of range can cause the 41 & 91 codes together. It will not cause a single code, only both codes together.

Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness. The exception is that the 94-95 uses a 4 wire O2 sensor.

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

Code 41 can also be due to carbon plugging the driver’s side Thermactor air crossover tube on the back of the engine. The tube fills up with carbon and does not pass air to the driver’s side head ports. This puts an excess amount of air in the passenger side exhaust and can set the code 41. Remove the tube and clean it out so that both sides get good airflow: this may be more difficult than it sounds. You need something like a mini rotor-rooter to do the job because of the curves in the tube. Something like the outer spiral jacket of a flexible push-pull cable may be the thing that does the trick.

If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.
 
You have two or more posts for the same probllem

What's the post number and where is it?

Code 41 or 91. Or 43 Three digit code 172 or 176 - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.

Revised 20-July-2017 to add note that the 94-95 uses a 4 wire O2 sensor.

Code 41 is the passenger side sensor, as viewed from the driver's seat.
Code 91 is the driver side sensor, as viewed from the driver's seat.

Code 172 is the passenger side sensor as viewed from the driver's seat.
Code 176 is the driver side sensor, as viewed from the driver's seat.

Code 43 is not side specific according to the Probst Ford Fuel injection book.

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Testing the O2 sensors 87-93 5.0 Mustangs
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear.

Disconnect the O2 sensor from the harness and use the body side O2 sensor harness as the starting point for testing. Do not measure the resistance of the O2 sensor , you may damage it. Resistance measurements for the O2 sensor harness are made with one meter lead on the O2 sensor harness and the other meter lead on the computer wire or pin for the O2 sensor.

Computer wiring harness connector, computer side.
View attachment 611595
Backside view of the computer wiring connector:
View attachment 611596

87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
The computer pins are 29 (L\RH O2 with a dark green/pink wire) and 43 (LH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
The computer pins are 29 (LH O2 with a Gray/Lt blue wire) and 43 (RH O2 with a Red/Black wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Testing the O2 sensors 94-95 5.0 Mustangs; note that the 94-95 uses a 4 wire O2 sensor.
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a red/black wire) and 27 (RH O2 with a gray/lt blue wire). Use pin 32 (gray/red wire) to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

Testing the O2 sensor wiring harness
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer. Using the Low Ohms range (usually 200 Ohms) you should see less than 1.5 Ohms.

87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Dark blue/Lt green wire in the LH O2 sensor harness and the Dark blue/Lt green wire on the computer pin 43
From the Dark Green/Pink wire on the RH Os sensor harness and the Dark Green/Pink wire on the computer pin 29

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 43
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 29

94-95 5.0 Mustangs:
Computer pin 29 Red/Black – LH O2 sensor
Computer pin 27 Gray/Lt blue – RH O2 sensor
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 29
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 27

There is a connector between the body harness and the O2 sensor harness. Make sure the connectors are mated together, the contacts and wiring are not damaged and the contacts are clean and not coated with oil.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

Check the fuel pressure – the fuel pressure is 37-41 PSI with the vacuum disconnected and the engine idling. Fuel pressure out of range can cause the 41 & 91 codes together. It will not cause a single code, only both codes together.

Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness. The exception is that the 94-95 uses a 4 wire O2 sensor.

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

Code 41 can also be due to carbon plugging the driver’s side Thermactor air crossover tube on the back of the engine. The tube fills up with carbon and does not pass air to the driver’s side head ports. This puts an excess amount of air in the passenger side exhaust and can set the code 41. Remove the tube and clean it out so that both sides get good airflow: this may be more difficult than it sounds. You need something like a mini rotor-rooter to do the job because of the curves in the tube. Something like the outer spiral jacket of a flexible push-pull cable may be the thing that does the trick.

If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.

im pretty sure i asked this question on someone elses post and when nobody said anything i made my own with hopes that someone would be able to help me with understanding the pin43 and 29 and how that they can be both lh and rh sensors off one wire.... if i could delete this post here i would but i dont kno how... thread i started is called
1992 lx testing o2 sensors with conflicting info about how to test......
 
91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
The computer pins are 29 (LH O2 with a Gray/Lt blue wire) and 43 (RH O2 with a Red/Black wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.
here are the instructions for testing the o2's for the 91-93 mustang
the instructions are clear, I think where you are getting confused is the instructions are copied and cover several years with the revisions shown in a different color.
 
91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
The computer pins are 29 (LH O2 with a Gray/Lt blue wire) and 43 (RH O2 with a Red/Black wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.
here are the instructions for testing the o2's for the 91-93 mustang
the instructions are clear, I think where you are getting confused is the instructions are copied and cover several years with the revisions shown in a different color.

Ok then explain to me this how can pin 29 be the RH 02 sensor and then pin 29 is the left hand???
 
Ok then explain to me this how can pin 29 be the RH 02 sensor and then pin 29 is the left hand???

Ok heres a better way to put it for me to understand What color wire goes to the driver side o2 and what color wire goes to the passenger O2

Because what im reading in the post for the 91-93 is that Pin 43 is the LH+RH o2 sensor and pin 29 is the RH+LH o2 sensor
It says Computer pin 43 is red/black-LH
Pin 29 Gray/lt blue-Rh o2 sensor..... Then below that it says Pin 29 LH o2 sensor and Pin 43 RH o2 sensor there is only one wire in the computer connection for Pin 43 and pin 29 so how can pin 29 be RH-LH and pin 43 be RH-LH
 
I didn't write test instructions, I agree it seems contradictory.
this is what I would do in your place, look at the wire colors at the o2's and match up to the computer pins.

Ok so im not going nuts then LOL cause im literally sittin here thinking that my brains fried and im seeing something wrong lol thanks for the help tho.. and yea im gonna have to lift my car and get under it to see what wire goes where... be the quickest solution im thinkin