In re-wiring my engine I noticed that the little brown wire from the alternator on my '89 Camaro V8 (originally 305, now 350ci) goes into the engine side of the bulkhead connector as it should, but there was no wire on the passenger side connector for it to plug into. I have an '87 Camaro wiring diagram that shows this wire going to the volt gauge (or light) on the instrument cluster, but there is no terminal for this wire on the printed dash circuit connector. I've read that this wire is necessary for exciting the alternator, but I'm perplexed why GM wired this like they did.

I went ahead and made a wire for the inside bulkhead connector and plugged it in the space to connector to the engine side brown wire from the alternator. I've read online that this needs to go to an ignition switched wire, but other than that I don't know what to do with it. Any information on this would be much appreciated.

As far as the car goes, a previous owner tried to do a TBI to carb swap when they swapped the original 305 for a 350 (and also tried to convert it to an Edelbrock carb). The engine harness was on the front seat when I got it, and it had been seriously butchered. It looked like basically the computer related wires were cut and the main engine electrical wire were still intact. The rest of the wiring looked like it had also been untouched. I basically copied the carbureted wiring diagram from my '87 Camaro factory service manual when I built my new harness, with a few minor exceptions. I believe the car would have originally had a CS130D alternator, but I've pretty much decided to switch to a 12SI alternator to try to simplify things since I've heard and read the the CS alternator have very finicky and fragile electronics (they were designed for use in computerized cars). As the previous owner was trying to do I'm wiring this car like an older Camaro without a computer.

 

Let me start by saying that your car has had the wiring altered,.. so only you can figure out what's what !!

I've got schematics from the 88 Camaro and they should be more accurate for your 89 than 87 diagrams simply because the entire engine bay wiring harness changed in 88. The 88 Shop manual shows that the BROWN wire from the Alternator should pass thru the firewall at the C100 connector PIN 'F8'. This appears to be true for all cars,... V6, V8 TBI, TPI, "dummy light" cluster or Gages cluster so If you don't have a wire on the dash harness 1/2 of the C100 connector - that's weird ! ( pretty sure all 84-89 cars had this wire at this location on C100)



I've got 2 schematics from the 8 Clusters,.. 1 for 'indicator' and 1 for 'gauges' cluster. They both show the BROWN wire as leading to cluster plug C1 and PIN 14. With the dummy light cluster the circuit feeds the VOLT warning light, with the gauges cluster it feeds the Voltmeter and a "hidden" volt telltale indicator. ( I assume the "hidden" indicator is just 1 of the telltale warning light ports that was unused on the gauges cluster ? )



Here is the wiring schematic for the 88 TBI ( and V6 ) charging system that shows the BROWN wire,.....



Again,.. I don't know what you've got in front of you, but these diagrams describe how that BROWN wire was originally configured and maybe that will help you solve your problem. Good Luck !

 

Like I described, I was originally missing the brown wire on the under-dash side of the circuit, and I don't have a terminal in the right space in my printed dash circuit connector as shown in your diagram (the space is empty). This part looks untouched as I also mentioned. The only thing I can think is in '89 the alternators they used at the plant this car was made at were self-exciting and didn't need the brown wire for that even though the brown wire was installed in the alt. connector. I'm also wondering if GM figured out a way to activate the volt indicator in the printed circuit with the computers these cars originally had, because there is a jumper wire running across the printed circuit to the approximate location of the "volt gauge" and all kinds of other weird looking stuff there.

I think I'll just run the brown wire I added to the dash side of the bulkhead connector to the ignition wire that ends up at the fuse box, then run a wire from there to an aftermarket volt meter. That way I have both bases covered, the alternator exciting and a way to see if the system is running at the correct voltage. This is a good example of why I hate printed dash circuits and computerized cars.

 

My understanding is the BRN wire is not necessary for alternator to function but it does add value.

The wire will land to the I terminal on a "PLIS" type alternator regulator, or to the F terminal on a "PLFS" type alternator regulator. I don't know which one you have in your car.

PLIS: From the factory, our cars use I (Ignition) terminal as a redundant/backup method to turn on alternator if L (Lamp) terminal bulb circuit fails. Either L or I will turn on the alternator, but each has different intended purposes and wiring requirements. Technically you could abandon L or I as long as one or the other is still used, but the charging system will be more robust with both. Sounds like in your case the I terminal has been abandoned?

PLFS: F terminal is a field monitoring circuit and is not necessary for alternator to function. I don't know that our cars even used F terminal for anything? Might just be blanked out or dead end somewhere.