I have a 1987 firebird 2.8 bone stock.I'm having problems with the vehicle charging.I had a bad alternator which I replaced but the pig tail plug in the back had a broken lock. This caused the plug to back out every few days which of course stopped it from charging . I replaced the pigtail with a new one from Napa and soldered it in place,everything worked great for about 4 weeks. In between everything working I had the starter go out so I replaced it,the charging system worked fine after the starter change.
The other night driving home the car stopped charging. I pulled over and pulled and tugged on the wiring harness for the alternator and it started charging again. I figured I had a cold solder joint in the splice for the pigtail. I resoldered the connections and it charged half way to work then dropped out again. I once again pulled on the harness and it started to work again. I thought maybe I had a bad plug from Napa,got a new plug and it worked fine in the driveway. I took a 30 mile drive and it stopped charging after about 20 minutes of driving....this time moving the harness did nothing it would not come back. I figure good it's really dead now I can find the problem.
This morning I checked the plug I have 12 volts on the red wire,12 volts on the tan wire with key on and nothing on black. This all looked good so I went and got a warranty swap on the alternator(the old one passed autozones bench test) But I said maybe it is failing when it gets hot so they gave me the new one. I put it on the car and it's still not charging,pulling on harness does nothing now. I jacked the car up and look at the bottom side of the harness,where it runs down towards the starter and everything looks good,connections on starter are good and tight. I start the car and now its charging again...wtf...So I set my multi meter up so I can see it under the car and I pull and tug on the harness from underneath the car,pushed on the starter connections,stays charging will not drop out. I get ready to leave for work and what do you know,it stopped charging again. I pop the hood pull on the harness and this time it starts working again. It stayed charging all the way to work this morning.
So I have really run out of ideas as to what is wrong. I would think a loose wire connection,bad wire,or bad eye loop on that starter would be my last few things to check. Anyone got any ideas? Thanks

 

Anyone? Maybe a wiring diagram for an 87?

 

Well... It seems you have a gremlin.

I hate those little buggers

I would venture on an internally corroded wire farther down the line.

Here's a link to wiring diagrams for all the 3rd gens, you can find yours by engine size and year.

http://www.austinthirdgen.org/index.php?pid=19

 

Thanks.I Guess I will just have to pull the harness apart and see what wire is bad.

 

I found the right link now.Looks like the brown wire goes all the way to the blower relay..ugh this is going to take awhile

 

NOT the blower relay, the COOLANT FAN relay by the brake booster. The terminals on the wires at these relays (fan and fuel pump relays) like to get hot and destroy the insulation on the inch or so of wire before it, causing shorts, and later, corroded wires. Best thing to do would be to start by replacing the relay connector as I'd be willing to bet at least 3 wires are damaged (the red or orange, the brown, and the black/red). And the same for the fuel pump relay next to it.

I replaced both of mine with a pair from an old alarm system I pulled out of another car. Relays are cheaper and no more wiring problems .

 

I think I found it.This is the 3rd wire on the plug and found this about 8 inches back in the harness.I guess it was shorting to ground.Did a test run tonight seems fine so far after wire replacment

 

That's awesome. Glad you found the culprit!

 

found this on the relay closest to the brake booster.Not sure what relay this is,has green wires and green with white stripe plus some lighter color wires.


the car stopped charging again on my way to work

 

well so far it is charging after fixing those relay wires. What does this relay have to do with charging?

 

The alternator sense wire (the brown one) is run off of the C/H FAN fuse in the fuse panel. The brown wire comes out of the bulkhead connector and runs to the radiator fan relay first, where it powers the relay coil. At the terminal at the relay, the brown wire splits off to the alternator connector around the back of the engine, down by the starter, and up the part of the harness running up to the throttle body (as you've already noticed). As I said before, both the fuel pump and fan relay terminals seem to like to get hot and damage the insulation on the ends of the wires closest to the terminals, which allows the water vapor in the air (and possibly coming under the hood from the cowl and up from the front of the car) to get at the hot wires, corroding them even faster. Corrosion causes resistance, resistance causes more heat, and the cycle continues until the wire can't send any decent amount of voltage to the intended source (the alternator's voltage regulator) due to the amount of resistance in the wire eating the voltage. And, of course, no power at the voltage regulator basically tells the regulator the system is turned "off" so it won't charge the battery.

:edit: And that relay connector in the pic above is for the A/C compressor... The one you're looking for has a big fat black and red wire coming out of it (which goes to the fan motor).

 

Ok if that is the a/c relay,then where is the coolant fan one? There are 2 mounted by the brake booster the one I fixed and one next to it close to the fender

 

Peel back the wire loom a couple inches so you can actually see the wire colors... Fan relay only has one green wire, the others are red, brown, and black with a red stripe. It's the only one with 4 wires. It may be hiding down by the bulkhead connector if it wasn't attached to the bracket.

 

Well I think that would be the one next to it then. I did look at that one and the wires appear to be ok,and the connector does not show signs of heat. I can tell you that at night with the a/c on ,headlights, That cause a good load on car of course...but it seems the blinkers really drag it down when I'am at idle,the volt guage will swing down under 13 volts

 

If you have a voltmeter, take the connector off of the alternator with the key turned on (and obviously the engine off). Should be 12V on all of the wires in the connector. There could also be an issue with the tan/white wire at the alt connector, which comes straight from the dash (no relay in the middle). I had a problem with this wire and someone replaced it incorrectly at the shop I had to replace the burned up alt at. Couple years later, I went through the harness and fixed this wire (and the radiator fan wire because he screwed with that as well) and the alt charging went from about 13V to 14.7V.

 

I have 14.5 .7 in the morning and carry 14 volts no problem untill it really get loaded with fan,headlights,blinkers,a/c..Also My alternator has 3 wires I do have my constant 12 volts, my switched 12 volts, and on the the third wire nothing there.

 

Again, there should be 12V on all 4 wires (the battery cable, the red power feed to the regulator, the brown sense wire, and the tan/white sense wire). Don't know why this is, when the other harness I have used with the 3.1 (from a 91) didn't have the tan wire and everything was fine, but apparently there is something about that tan wire that the alternator doesn't like if there isn't a 12V supply there.

 

well as you see in the top picture the wire that was chaffed through is the third wire on the plug.It does not have 12 volts this is a black wire. So what your saying is I need switched 12 volts on the other 2 wires on the plug. I do have switch on the middle wire the tan wire. I wonder If I could just tie the 2nd and 3rd wire together for switched 12 volts