Fuse # 1 Keeps blowing when car is put into reverse

MustangX

Dirt-Old 20+Year Member
Jul 10, 2002
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1
Virginia, USA
I just picked up a sweet 1996 GT Vert, 5-spd, Bone stock and I've had to replace the #1 fuse 4 times already, everytime it blows the air bag light comes on and the turn signal lamps stop working.

I now figured out what was causing my number 1 fuse (15a) to blow out
Almost Everytime (99%) I put the car into reverse it blows out, I unpluged the power that goes the tail light assembly, still blew the fuse so I dont think it's the reverse bulbs.

Is there a "reverse sensor" somewhere that might have shorted, like on the tranny, that may be causing it to blow the fuse

Some more symptoms, when the fuse blows, the hazards still work, as well as all 3 sets of brake lights (still light up), so I am confused....

jeez this is annoying...:bang: but thank god it just passed inspection!!!! :shrug:

Thanks in advance
 
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These are the items that run off of that fuse

Turn Signal Lamps
Back-Up Lamps
Air Bag Module
Overdrive Cancel
Brake Shift Solenoid
Heated Backlite relay coil
Conv. top relay coil
Illum. entry module (shut off)

I am thinking the Back-up lamps+the Brake sensor is causing the fuse to blow,
I realized that the fuse seems to only blow if I have my foot on the brake pedal, and putting it in reverse.
where can I get a new brake pedal sensor?

Thanks again.
:nice:
 
I am thinking the Back-up lamps+the Brake sensor is causing the fuse to blow,
I realized that the fuse seems to only blow if I have my foot on the brake pedal, and putting it in reverse.
where can I get a new brake pedal sensor?

Thanks again.
:nice:

As much of a PITA it would be to run around chasing wires, just throwing a sensor at it and hoping for the best will not solve your problem.

IMO, replacing that wont do a thing. If your brake lights illuminate when you hit the brake pedal, that switch is fine and you're doing yourself no good to replace it. You're most likely culprit is a short to ground and its overloading the circuit.
 
As much of a PITA it would be to run around chasing wires, just throwing a sensor at it and hoping for the best will not solve your problem.

IMO, replacing that wont do a thing. If your brake lights illuminate when you hit the brake pedal, that switch is fine and you're doing yourself no good to replace it. You're most likely culprit is a short to ground and its overloading the circuit.

COramprat said:
Has it happened other times when not putting it in reverse? If that is the case you have narrowed it down a bit. Problem is chasing a short is a pain but it can be done.

Okay so today the fuse blew again, but this time it was only by just putting the the car into reverse (no using brakes, so Dragstr05 you're right). I am wondering if the backup lamp switch on the tranny is shorting
:bang: :bang:

COramprat, it only happens in reverse, so everytime I park somewhere I make sure I am facing forward

I gonna put it on a lift tommorow, maybe stupid cable for the switch melted on the exhaust. hopefully it's something simple
:bang:
 
Put the car on a lift, everything checked out fine underneath, so i guess it's time to bust out the volt/ohm meter, circuit tester, in the mean time I unplugged the backup lamp swtich, and that help by not blowing the fuse, I think turn signals are more important that reverse, so in until I figure out the issue, I'll just stick my head out the window and yell out that I am reversing and play the ludacris song, "move bish, get out the way...." :shrug:

Does anyone have a reverse light wiring diagram for a 1996 gt vert?

will post once I figure out what the problem is.
 
Put the car on a lift, everything checked out fine underneath, so i guess it's time to bust out the volt/ohm meter, circuit tester, in the mean time I unplugged the backup lamp swtich, and that help by not blowing the fuse, I think turn signals are more important that reverse, so in until I figure out the issue, I'll just stick my head out the window and yell out that I am reversing and play the ludacris song, "move bish, get out the way...." :shrug:

Does anyone have a reverse light wiring diagram for a 1996 gt vert?

will post once I figure out what the problem is.

This is a simple circuit. I'm assuming a 5-speed, if that is wrong, then the only difference is in the switch.

The short has to be between the switch and the backup lights. If it were in front of the switch, it would always be shorted and you would not see the symptom you are seeing.

Look at the backup lamp switch. Should have a purple/orange wire going in, and a black/pink wire coming out. That wire goes to the back of the car and powers the backup lights. I would be tempted to start at the backup lights themselves and check the lamp sockets and the wire coming out of the socket to make sure that all looks reasonable.

I'd start like this:

1. visible inspection of the lamp sockets.

2. Next take an ohmmeter and connect to the black/pink wire at the reverse lamp switch, connect other probe to ground (easier if you remove the backup lamp bulbs). Circuit with bulbs out should be an open circuit, infinite resistance. With bulbs in, it will not be open, the resistance you read will be the resistance of the bulbs which will make it more confusing. Remove 'em. If you find 0 ohms you now know that between the switch and the lamp socket there is a dead short to ground.

I am not sure how the wiring goes between the two lamps, but it probably comes in on one side of the trunk and runs all the way across to the other lamp. Anywhere along that path is a potential problem.

If you remove the lamps and get an open circuit, you could have a bulb with an internal short. Or you might have opened the circuit when you wiggled the wire, again letting you know that the short is "close by".

Best bet is right around the socket or else where the black/pink wire comes out of the "bundle" and goes to the light assembly.
 
Thanks BobHyatt!!

This is a simple circuit. I'm assuming a 5-speed, if that is wrong, then the only difference is in the switch.

The short has to be between the switch and the backup lights. If it were in front of the switch, it would always be shorted and you would not see the symptom you are seeing.

Look at the backup lamp switch. Should have a purple/orange wire going in, and a black/pink wire coming out. That wire goes to the back of the car and powers the backup lights. I would be tempted to start at the backup lights themselves and check the lamp sockets and the wire coming out of the socket to make sure that all looks reasonable.

I'd start like this:

1. visible inspection of the lamp sockets.

2. Next take an ohmmeter and connect to the black/pink wire at the reverse lamp switch, connect other probe to ground (easier if you remove the backup lamp bulbs). Circuit with bulbs out should be an open circuit, infinite resistance. With bulbs in, it will not be open, the resistance you read will be the resistance of the bulbs which will make it more confusing. Remove 'em. If you find 0 ohms you now know that between the switch and the lamp socket there is a dead short to ground.

I am not sure how the wiring goes between the two lamps, but it probably comes in on one side of the trunk and runs all the way across to the other lamp. Anywhere along that path is a potential problem.

If you remove the lamps and get an open circuit, you could have a bulb with an internal short. Or you might have opened the circuit when you wiggled the wire, again letting you know that the short is "close by".

Best bet is right around the socket or else where the black/pink wire comes out of the "bundle" and goes to the light assembly.

This sounds like a good plan of action and is how I will proceed to further troubleshoot the issue.

THANKS,
:nice: :nice:
 
Do you guy's happen to know if this is a reverse polarity curcuit (or whatever it's called). Meaning, does the hot lead run through the bulbs, THEN to the back up switch? Instead of to the switch, then bulbs, which would make sence. Base on what you're saying, it's not reversed. I have this same problems with my 94 auto V6 convertible. Same curcuits I'm sure, except the around the tranny. My problem is the fuse WILL ALWAYS blow out with a hot engine (in foward, reverse and park). And it WILL NEVER blow with a cold engine (also in any gear). I have already removed most other things on that curcuit (air bags, air bag module, turn signal switch, rear defroster switch, rear defroster harnesses at the back window, center console with convertible switch, and AOD override).

MustangX, I'll keep you posted on everything I find. We might be dealing with a chafed or crimped wire, or god know what else, in the same location.
 
update

thanks me27821, ur probably in a worse situation since yours is an auto, u go from P to R. if I didnt have get inspection every year, I wouldnt even bother fixing it, and would keep playing the ludacrais song, :lol: BUT, unfortunately that's not the case, on the auto trannys there is a tranmission range sensor and a backup lamp switch.
not sure how that works on an AT.

Today I tested (ohms) the blk/pnk line and it appeared to be good, so now I am scratching my head again, :( so for S&G I'm gonna buy the damn switch and replace it to see what happens, the previous owner, didnt drive the car much only about 3000 miles avg a year, so I am thinking since it's sat most of its life (outside) the backup light switch my have corrosion inside...ARGH sigh...
 
thanks me27821, ur probably in a worse situation since yours is an auto, u go from P to R. if I didnt have get inspection every year, I wouldnt even bother fixing it, and would keep playing the ludacrais song, :lol: BUT, unfortunately that's not the case, on the auto trannys there is a tranmission range sensor and a backup lamp switch.
not sure how that works on an AT.

Today I tested (ohms) the blk/pnk line and it appeared to be good, so now I am scratching my head again, :( so for S&G I'm gonna buy the damn switch and replace it to see what happens, the previous owner, didnt drive the car much only about 3000 miles avg a year, so I am thinking since it's sat most of its life (outside) the backup light switch my have corrosion inside...ARGH sigh...

Let me make sure I understand. First, remove the tail lamps. Now try the test by putting it in reverse. Does it blow? If so, you know the short is between the bulb and the switch or the switch and the front of the car (so far as I know, the +v comes from the front of the car, thru the switch, to the lamps and then to ground in the rear.

One thing I did not mention, the switch itself can be bad. You could verify this by using a jumper to connect the switch connector from the front +v source to the switch, but do not connect the other pin to the black/pink wire going back to the lampa. If it blows now, the switch itself is bad and should be replaced, as it is responsible for grounding the +V. Again, I like to confirm before buying, so you can do this:

Unhook the connector and take your ohmmeter and connect it to the +v pin (not the black/pink wire). Connect the other probe to ground. In park you should be seeing "open circuit". Now shift into reverse. If it goes to 0 ohms, it is shorting +v to ground inside the switch and the switch is bad. If it passes that test, swap the ohmmeter to the other pin and do the same test. Again, you should never see 0 ohms. If either pin gets shorted to ground, replace the switch and your problem will be fixed. If not, you still have to have a shorted connection from the switch on back.
 
Let me make sure I understand. First, remove the tail lamps. Now try the test by putting it in reverse. Does it blow? If so, you know the short is between the bulb and the switch or the switch and the front of the car (so far as I know, the +v comes from the front of the car, thru the switch, to the lamps and then to ground in the rear.

One thing I did not mention, the switch itself can be bad. You could verify this by using a jumper to connect the switch connector from the front +v source to the switch, but do not connect the other pin to the black/pink wire going back to the lampa. If it blows now, the switch itself is bad and should be replaced, as it is responsible for grounding the +V. Again, I like to confirm before buying, so you can do this:

Unhook the connector and take your ohmmeter and connect it to the +v pin (not the black/pink wire). Connect the other probe to ground. In park you should be seeing "open circuit". Now shift into reverse. If it goes to 0 ohms, it is shorting +v to ground inside the switch and the switch is bad. If it passes that test, swap the ohmmeter to the other pin and do the same test. Again, you should never see 0 ohms. If either pin gets shorted to ground, replace the switch and your problem will be fixed. If not, you still have to have a shorted connection from the switch on back.


Bob,
I removed the tail lights checked the reverse bulbs, socket and bulbs appear to be clean and no corriosion on point of contacts or any signs of "burnage", I then also removed the tail light harness (power) completely off the tail lights and it still blew the fuse, I then checked the blk/pnk cable and it appears to be good. One thing I did forget to be more detailed about is that the fuse blowing; happens about 95% of the time. The fuse does not always blow when putting it into reverse, which is why i keep thinking it's the Backuplamp switch. Sometimes In one day I can reverse 4-5 times and it wont blow, but sometimes, the first time I put it in reverse it blows, to me that sounds like a bad switch. With the switch being disconnected it is not blowing the fuse at all, so I am thinking that from the fuse box to the switch the line is good, and I am gonna test that switch tommorow for ohms, but eitherway I'm still gonna replace it, for all I know, when I test it, it could be that 5% chance that it is working and its a $17 part, so I wont feel too bad, I just hope it fixes the issue.

And Thanks for your help again!!:nice:
I appreciate your input on this issue, even tho I got an A in high school physics, I knew I should have paid more attention in class, and took some more classes when I was in college.. :lol:
 
Already a step ahead. 04 Red GT Convertible. It's already parked in the old Mustang's spot. I just spent 9 hours cleaning, detailing, and waxing the old one. I'm gonna take some pics and put it on craigslist tomorrow. It's too dark for pics now. That thing better be shiny as hell when the sun comes up. 9 freakin hours.
 
Bob,

What color is the +v wire?

Thanks

purple/orange into the switch. black/pink out of the switch to the tail-lamps and on to ground.

Really sounds like the switch itself might be the culprit... Clearly it is the switch or farther back.... Also I don't know how your tail lamps look, but I just worked on a GM1500 that had a set of lamp sockets on a circuit board, and there was a nearly invisible short on the circuit board itself that was making the backup lights turn on the tail lamps...
 
Bob,
I removed the tail lights checked the reverse bulbs, socket and bulbs appear to be clean and no corriosion on point of contacts or any signs of "burnage", I then also removed the tail light harness (power) completely off the tail lights and it still blew the fuse

Also I don't know how your tail lamps look, but I just worked on a GM1500 that had a set of lamp sockets on a circuit board, and there was a nearly invisible short on the circuit board itself that was making the backup lights turn on the tail lamps...

Its possible that it has that problem also but with the harness disconnected from the tail lights it still poped the fuse. I'm wondering if the switch IS the problem after all.