Hatch/Trunk Mounted Battery Ground Location...

chitownstang1 said:

I'm leaning towards the battery charger thing as misleading. I typically will charge the battery while not connected to the car resetting the computer. Since ditching the charger theory/idea the battery is 12.+v every morning.

Key One Engine Off: I checked the LtG/R wire at the alternator and got 12.8v but when plugged in it was 3.8v?

I'll start drop voltage testing tomorrow. With the way the computer/car can run great then not that seem to coincide with the low oil and possibly the coolant dash lights, the slight buzz in the stereo, there's more to this but in a nutshell this really feels like some type of short.

It's fun to mess around with the Stang from time to time but this is starting to take it's toll. Countless hours and very few cruises this season, well, sucks.

Thanks everyone for your help.

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Go back and look at the alternator diagram. There is a resistor and a indicator lamp in series with the switched 12 volts. You are seeing the voltage drop across them, which is to be expected. Anytime you pass current through a device, be it a resistor, lamp, solenoid, motor, coil or whatever, there will be voltage drop across that device. It's known as Ohms Law.

If you did see a full 12 volts, with the green wire plugged in, it would be a cause for concern.

I was curious between the 2.4v you mentioned on your test vehicle vs. the 3.8v's I read from mine; Key On Engine Off while connected. Sounds like the main thing is it's not reading 12v. So I past that test.

Any idea what the meaning behind the oil light functioning properly and the car running well vs. not could be? And where does that wire come from and then go too, color? If anyone knows?

I could again be totally off with the direction i'm going but if I disconnect the battery and the computer resets itself it'll run well for a few miles then slip back into an almost limp mode. It's sharp, crisp throttle, very responsive, then it's back to a point you can drive it but not without thinking it's causing harm.

EDIT: Unless there is something failing that is intermittent so at times i'm getting 12 volts and other times 3.8v?

I have 2 connections - One to the quad shock mount - the other to one of the bolts on the starter . . .haven't had any issues yet - Although to be honest, having the battery in the back if my hatch makes me uneasy sometimes. . . .

Gotta do mine as well now since the tube front going in.

So run neg off battery to quad shock mount ground clean, bolted obviously. Then from there to the block. Positive goes to starter solenoid. Dont have my car to look at and im stupid.

So i should just run 1/0 for the positive from the battery also? All the kits have 2 ga.

Ie: https://www.jegs.com/i/JEGS+Perform...F5JcUAeB1RRLjoWgTVarE8dVxDT_S2_UaAl7dEALw_wcB

Foxslider said:

So i should just run 1/0 for the positive from the battery also? All the kits have 2 ga.

Ie: https://www.jegs.com/i/JEGS+Perform...F5JcUAeB1RRLjoWgTVarE8dVxDT_S2_UaAl7dEALw_wcB

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This is a very old thread. 1/0 is better. I've run welder lead wires with good results. Make sure its copper wire and not copper clad aluminum. Clean ground to quad shock bolt and the engine block. There should be another ground from the block to the sway bar mount on the left side. ( drivers side ). Positive straight to the solenoid. I use a power block from a mid 80s to mid 90s chevy pickup or full size truck. Its located on the passenger side of the firewall and has 5 lugs on it. I run the newer starter and it makes the wiring a lot easier. Hard to fit everything on the one post of the solenoid.

Cool. Preciate the input. Just watched house of dula install his. Minus the labor easy to understand.

So just run a 4ga? From the solenoid to the powerblock? Then attatch the 4ga alternator power cable to the powerblock.

Foxslider said:

Cool. Preciate the input. Just watched house of dula install his. Minus the labor easy to understand.

So just run a 4ga? From the solenoid to the powerblock? Then attatch the 4ga alternator power cable to the powerblock.

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Rear mounted battery ground wiring. Follow this plan and you will have zero ground problems.


Rear mounted battery wiring recommendations

For a battery cut off switch, see https://www.moroso.com/catalog/pro...rnator-disconnect-switch74108/category/3114/
is the switch
https://www.moroso.com/pub/media/instructions/74108_instweb.pdf is the installation instructions.

Switch picture...

Use the super duty switch and the following tech note to wire it and you will be good to go.

Use the Moroso plan for the alternator wiring and you risk a fire. The 10 gauge wire they recommend is even less adequate that the stock Mustang wiring.

There is a solution, but it will require about 40' of 18 gauge green wire.

Wire the battery to the two 1/2" posts as shown in the diagram.

The alternator requires a different approach. On the small alternator plug there is a green wire. It is the sense lead that turns the regulator on when the ignition switch is in the run position. Cut the green wire and solder the 40' of green wire between the two pieces. Use some heat shrink to cover the splices. See http://fordfuelinjection.com/?p=7 for some excellent help on soldering & using heat shrink tubing.

Run the green wire back to the Moroso switch and cut off the excess wire. Try to run the green wire inside the car and protect it from getting cut or chaffed. Crimp a 18 gauge ring terminal (red is 18 gauge color code for the crimp on terminals) on each wire. Bolt one ring terminal to each of the 3/16" studs. Do not add the jumper between the 1/2" stud and the 3/16" stud as shown it the
Moroso diagram.

How it works:
The green wire is the ignition on sense feed to the regulator. It supplies a turn on signal to the regulator when the ignition switch is in the Run position. Turn the Moroso switch to off, and the sense voltage goes away, the voltage regulator shuts off and the alternator quits making power.

The fuse & wiring in the following diagram are for a 3G alternator. The stock alternator uses a dark green fuse link wire that connects to 2 black/orange wires. Always leave them connected to the starter solenoid even if you have a 3G alternator.





Rear mounted battery ground wiring. Follow this plan and you will have zero
ground problems.

One 1 gauge or 1/0 gauge wire from battery negative post to a clean shiny spot on the chassis near the battery. Use a 5/16” bolt and bolt it down to make the rear ground. Use a 1 gauge or 1/0 gauge wire from the rear ground bolt to a clean shiny spot on the block.

One 4 gauge wire from the block where you connected the battery ground wire to the chassis ground where the battery was mounted up front. Use a 5/16” bolt and bolt down the 4 gauge engine to chassis ground, make sure that it the metal around the bolt is clean & shiny. This is the alternator power ground.




The computer has a dedicated power ground wire with a cylindrical quick connect (about 2 ½”long by 1” diameter. It comes out of the wiring harness near the ignition coil & starter solenoid (or relay). Be sure to bolt it to the chassis ground in the same place as you bolted the alternator power ground. This is an absolute don’t overlook it item for EFI cars
Note: The quick disconnect may have fallen victim to damage or removal by a previous owner. However, it is still of utmost importance that the black/green wires have a high quality ground..

Picture courtesy timewarped1972

Crimp or even better, solder the lugs on the all the wire. The local auto stereo shop will have them if the auto parts store doesn't. Use some heat shrink tubing to cover the lugs and make things look nice.


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring
http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

Thanks, will do.

Where does that chassis ground terminate specifically?

I started tracking the chassis ground from the neg side of starter solenoid earlier, car wasnt jacked up so could'nt see where it terminated at. The battery ground was to the block. I lost it at the passenger control arm area.

Foxslider said:

Thanks, will do.

Where does that chassis ground terminate specifically?

I started tracking the chassis ground from the neg side of starter solenoid earlier, car wasnt jacked up so could'nt see where it terminated at. The battery ground was to the block. I lost it at the passenger control arm area.

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Grounds

This checklist applies to all Mustangs, not just the EFI equipped cars. Some of the wiring will be different on carb cars and carb conversions

Revised 26 –Oct -2016 to add fuel pump ground to the list.

Grounds are important to any electrical system, and especially to computer controlled engines. In an automobile, the ground is the return path for power to get back to the alternator and battery.

Make sure that all the ground places are clean and shiny bare metal: no paint, no corrosion.

1.) The main power ground is from engine block down by the oil filter to battery: it is the power ground for the starter & alternator.


2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. The clue to a bad ground here is that the temp gauge goes up as you add electrical load such as heater, lights and A/C.

Any car that has a 3G or high output current alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects. The 3G has a 130 amp capacity, so you wire the power side with 4 gauge wire. It stands to reason that the ground side handles just as much current, so it needs to be 4 gauge too.

The picture shows the common ground point for the battery, computer, & extra 3G alternator ground wire as described above in paragraph 2. A screwdriver points to the bolt that is the common ground point.

The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
Picture courtesy timewarped1972


Correct negative battery ground cable.

3.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally: it comes off the ground pigtail on the battery ground wire. Due to its proximity to the battery, it may become corroded by acid fumes from the battery.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness.

All the grounds listed in items 1,2 & 3 need to bolt to clean, shiny bare metal. A wire brush or some fine sandpaper is the best thing to use to clean the ground connections.


4.) All the sensors have a common separate signal ground. This includes the TPS, ACT, EGR, BAP, & VSS sensors. This ground is inside the computer and connects pin 46 to pins 40 & 60, which are the main computer grounds. If this internal computer ground gets damaged, you won't be able to dump codes and the car will have idle/stall/ performance problems

5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is an orange wire with a ring terminal on it. It is located in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or bolt on back of the cylinder head.

6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself. The TFI module ground terminates inside the computer.

7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.

8.) Fuel pump ground the fuel pump has a ground pigtail the connects to the body under the gas tank. You have to drop the gas tank to see where it bolts to the body.



See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help troubleshooting voltage drops across connections and components. Be sure to have the maximum load on a circuit when testing voltage drops across connections. As current across a defective or weak connection, increases so does the voltage drop. A circuit or connection may check out good with no load or minimal load, but show up bad under maximum load conditions. .

Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch
100 mV Ground
0 mV to <50 mV Sensor Connections
0.0V bolt together connections



]

Extra grounds are like the reserve parachute for a sky diver. If the main one fails, there is always your reserve.

The best plan is to have all the grounds meet at one central spot and connect together there. That eliminates any voltage drops from grounds connected at different places. A voltage drop between the computer ground and the alternator power ground will effectively reduce the voltage available to the computer by the amount of the drop.