Electrical 89 GT Alternator upgrades, battery not holding charge

FetusLasVegas · Apr 6, 2019

Bought a brand new battery. Tested alt again and it’s good. Looks like somehow swapping an alt created some kind of problem with the grn/red wire. Now how do I fix this??

Blown88GT · Apr 6, 2019

Check all voltages at the battery with engine off & then with engine running.
Good battery is 12.65V with engine off.
Good charging system is 14+V with engine running.

FetusLasVegas · Apr 7, 2019

Blown88GT said:
Check all voltages at the battery with engine off & then with engine running.
Good battery is 12.65V with engine off.
Good charging system is 14+V with engine running.

I think through the troubleshooting process, the green/red wire is the issue, I don’t know how this problem came out of nowhere, but I have a working brand new battery and alternator. So, what do I do now to get my daily driver running?

FetusLasVegas · Apr 7, 2019

Blown88GT said:
Check all voltages at the battery with engine off & then with engine running.
Good battery is 12.65V with engine off.
Good charging system is 14+V with engine running.

I’ll check in the morning and post...

Blown88GT · Apr 7, 2019

Maybe you have a burned out fuselink, E or F. They cannot be tested with an ohmmeter, 1 wire strand remaining will still show 0 ohms. Look for melting or a soft spot.

FetusLasVegas · Apr 7, 2019

Blown88GT said:
Maybe you have a burned out fuselink, E or F. They cannot be tested with an ohmmeter, 1 wire strand remaining will still show 0 ohms. Look for melting or a soft spot.

Will do. Is there a fuse link on the grn/red wire? Where are they located. I tried to find them over by the starter solenoid and couldn’t find anything.

Blown88GT · Apr 7, 2019

The wire colors are shown on the drawing. The starter relay is a bit obscured by the fat blue wire.
If I can see them, so can you.
If a PO has moved them to "tidy up" the engine compartment, can't help you.
This is a fuse link replacement. Looks like a piece of wire & it is of a sort, special wire & special insulation.

FetusLasVegas · Apr 7, 2019

Blown88GT said:
The wire colors are shown on the drawing. The starter relay is a bit obscured by the fat blue wire.
If I can see them, so can you.
If a PO has moved them to "tidy up" the engine compartment, can't help you.
This is a fuse link replacement. Looks like a piece of wire & it is of a sort, special wire & special insulation.

The fuse links all look good.

FetusLasVegas · Apr 8, 2019

Blown88GT said:
Maybe you have a burned out fuselink, E or F. They cannot be tested with an ohmmeter, 1 wire strand remaining will still show 0 ohms. Look for melting or a soft spot.

So, I followed the path of the green/red wire in the engine bay. It goes into a 3 pin connector on the firewall side of the battery. I undid the connector and tested for battery voltage on the firewall side with the key on. Bingo!! Read the same voltage as across the battery posts. Looks like there is some wiring problem between the 3 pin connector and the alternator. I ran a bypass wire from the firewall side of the connector and spliced it in at the d connector at the alternator and everything is perfect now. The bypass wire was just used to troubleshoot, so now I have questions about a proper fix.

1. Any suggestions on where to get lt green with red tracer 16ga wire? Checked the hardware store with no luck. Will an auto parts store have it, or should I just order it online?

2. Same question on where to source the individual female side pin connector that snaps into the 3 pin connector.

3. I figured I would run the new properly colored wire along the stock harness and pin it in the connector correctly. Is there a better way to fix this or do I have it all figured out??

Blown88GT · Apr 9, 2019

1. You're not going to find the same color.
2. Since the bypass wire works, can't you make it permanent? I have no pic of the 3 pin connector, but you might be able to find one in a JY & cut it off, keeping the wire pigtails so you have something to splice on to.
3. If you tie-wrap the bypass wire to the green/red wire it might be a reminder to you or any future owner. You could try to hunt down the "break" in the green/red wire. Are you sure it's not the Alternator Warning Indicator Lamp that's burned out or missing?

Here's where the green/red wire makes the connection.

FetusLasVegas · Apr 9, 2019

Blown88GT said:
1. You're not going to find the same color.
2. Since the bypass wire works, can't you make it permanent? I have no pic of the 3 pin connector, but you might be able to find one in a JY & cut it off, keeping the wire pigtails so you have something to splice on to.
3. If you tie-wrap the bypass wire to the green/red wire it might be a reminder to you or any future owner. You could try to hunt down the "break" in the green/red wire. Are you sure it's not the Alternator Warning Indicator Lamp that's burned out or missing?

Here's where the green/red wire makes the connection.

Thanks again for all your help.

1. 4rcustomswire.com has custom color to match gxl wire in 5ft increments with free shipping. I found lt grn with red tracer.

2. The reason I’m not making the current bypass permanent is all I had to use for it was 14ga speaker wire. I’ll take a pic of the connector and post it up later. I was able to find the wedgelock pin terminal at Napa and will pin the end of the proper wire once I receive it to put everything back as close to stock as possible.

3. When I have more time, I will pull the whole length of the alternator harness and run all new wire and loom it properly. I know it’s not the bulb or resistor because per the troubleshooting instructions posted way back in the beginning of the thread I tested all that when I found out the green/red wire wasn’t getting the proper voltage at the alternator harness. For anyone who has this issue in the future, I recommend testing for battery voltage at the firewall side of the 3pin with the key on engine off to figure out if the problem is due to a burnt bulb or bad resistor. It’s way easier and faster than pulling out the gauge cluster.

Electrical 89 GT Alternator upgrades, battery not holding charge

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