Just finished fixing starting problems and now the altenator is eating batteries. We can finally start the 1988 GTA, but the amp meter in the car is only showing 8 volts, not the normal 13 to 14 volts. So, we take the altenator off of my other sons' 91 firebird and the same thing is happening. Only 8 volts showing. We can only drive the car a few blocks before the battery dies out. I check the wiring diagrams in the Haynes manual and it appears that there is a inline fuse back to the battery. Located the fuse and it is not blown. All fuses under the dash are good also. The cable from the back of the altenator is correctly leading back to the positive side of the battery. I will take both of the altenators to Oreillys' tomorrow and have them checked. Any other ideas? Jim Berry.

Sounds like you may have a short somewhere. Have you checked for hot wires, lights not turning off, power windows stuck?

All lights work as they are supposed to, so far. I took the GTA altenator into Oreillys and it cleared all checks as good. When we start it, we are only able to run it about 10 minuites before the battery charge is gone. I searched down some of the wires and found one in-line fuse and it was okay. Going to the junkyard tomorrow to shadow some wires and find the connectivity points and maybe swap them out.

Jim B.

Before you even attempt to diagnose electrical problems, make sure the battery is fully charged, can hold a charge and can pass a load test.

If the battery isn't fully charged and can hold it, you're just spinning your wheels.

How and where are you reading the battery voltage? With a volt meter across the battery or by looking at the dash gauge?

I get the batteries recharged at Oreillys and they test them prior to leaving. Battery starts strong. We were able to get a full 14 volt reading from the dash gauge yesterday and my son was able to take the car around the block. Upon returning to the driveway, we were back to 8 volts and a dying battery.

I could not repeat the 14 volt reading this evening. With the car running and moving wires around again, I still could not get the 14 volt reading. Continuity checks along the gound wire and poitive return from the altenator to the battery were good. Used a craftsman multimeter.

Jim Berry.

It sounds like your exciter wire is not getting the voltage feed back it needs.
I had the same fun your haveing a couple of months ago.

the big wire off of the back of the alt. should go to the battery or the main (big) terminal on the starter. (obviously)

plug on alt has 2 wires

big red wire goes to same place as the previous wire

the other wire (maybe white) is the Voltage sense wire ( alt won't charge without it)
this one is a switched V source.
Just to test you can connect a wire from your battery to this wire with a small resistance in line (wire a bulb in there ) and you should see 13 - 14 V at the battery.

This wire was my problem ... I couldn't find the source of the break (and have a better wireing harness in a parts car that I plan on transplanting soon ) so I did a stupid splice job into my hot wire at the distributor. I wouldn't have done it this way if I didn't plan on ripping it all out this spring (P.O. hacked the existing harness badly ... and must have gotten a good deal on 14Ga. GREEN wire, 'cause I've got dozens of green wires under the hood)

hope it helps
Tony

here is a link that might help
http://www.hotrodders.com/forum/gm-3...up-154278.html

uemf, you have a different alternator... His is a CS series.

Anyways, there are 3 wires that are supposed to be hot with the ignition on. The one on the screw post, the big red one, and the brown one (I assume the L98 TPI, otherwise for the VIN H it's a brown/white wire). The big red one comes from the starter, and has a fusible link. The brown (brown/white) wire comes off of the C/H FAN fuse in the fuse block. And the white wire is for the dash gauge. I know that when I had problems with mine and had the car fixed at a truck shop in PA the guy rewired it and screwed it all up and had the alternator barely charging (due to a bad FAN fuse, nonetheless), except around 13.5 volts or something of the sort. I ended up replacing about a foot of wire along with the alternator connector to get her charging back at 14.7 VDC. You may end up tracing a good deal of wire to fx the problem. BTW, the Haynes manual lists the sense wire (that brown one again) as a resistance wire... It's not.

:edit: BTW, the car should normally be charging in the ballpark of 14.5 VDC... Halfway between 13 and 16 VDC (as stated by my FSM).

My bad. My bird has the serpentine setup off of a 90s and a CS alt. , My parts car is a 86 and has a SI Alt. (and is stored 45 miles away)
was working from memory . (that's always dangerous for me)
Sorry if I misinformed.
Tony

It happens, especially with all of the changes GM made between the 86 and 87 model years... The change in the alternator was one of those.

Correct. This alt has the three wires. I'm totally befuddled with this one. The PO couldn't figure out that the fan relay had gone, and just wired a hot lead to the fans. If this affects the alt, not sure but still troubleshooting. Got a pigtail from a 88 chevy caprice and may have time to splice it in tomorrow.

Are you sure it was just the relay that was bad? Chances are that either the C/H FAN fuse is blown or the brown wire is bad. Check for battery power at both fan relays at terminal "D".

As soon as it gets a little warmer down here. I'll pop the hood!

Jim Berry

Worked on it again today. Still not seeing the 14.7 at the dash gauge. Took the battery to Oreillys for a charge and they said it was bad gave me a new battery. Still the same condition. I will try splicing into the white wire of the three off the pigtail and see what happens. I will also get a new fan relay later this week.

Dash gauges are usually inaccurate. Until I manually set mine, it read closer to 13V than what was coming out of the alternator. Take a measurement at the battery.

We got under the hood today. I did two things: 1) I ran another wire from the alt to the battery directly. 2) Ran another wire from the alt to the white wire on the pigtail. I now see the voltmeter in the car at about 13 volts. With the car running I see 14.5 volts at the battery now. We will run the car for a few days and see if this holds.

Jim Berry

don't know if this has been advised, but check your power wire that goes from the alternator bolt back to the battery... you may not be supplying the juice the alternator needs to create a charge... on my bird, I had to use good ol' battery gauge cable, my amp draw would keep melting the cable, now I have no problems with it.. or I should say I did not have any trouble for about a year ... right now it's garaged...

I had the same problem alternator would not charge the battery it was a blown fan fuse that is where the alt gets its power. Replaced the fuse and now it charges up to 14 volts again.

Just purchased one yesterday. Going to have a small get together tomorrow and will replace it this weekend.

Finally installed the new fan relay. Car works fine now and I removed all of the "jerry" rigged items. We are able to drive the car and actually burned the rear tires for a few seconds. Thanks for the help.

Jim Berry

Good news glad to hear that your bird is back on the road.