1987 corvette alternator won't hold charge

[RStovall]

If we put power on the brown wire it turns on the battery light if just grounding it doesnt do anything

 

[ecss]

So the brown wire goes from the alternator to the regulator and thats what makes the bulbs in the cluster light up? If so alternator is new and checked out fine, where is the regulator? (sorry wiring in not my forte)

I know I have one small red, one small blue and one small brown wire.

If you unplug the connector at the alternator.
Turn the ignition On.
Ground the Brown wire the battery indicator should light. That proves the circuit works.

The regulator is built into the alternator.
The regulator grounds the Brown wire if the alternator voltage output is out of spec.
Such as the voltage is to low or to high. The small red sense wire monitors
the battery voltage and that's how it knows what voltage is needed to charge the battery.

The Large Red wire at the alternator battery stud is the output voltage of the alternator and
is the voltage that charges the battery.

The alternator case is the ground for the alternator. You should have zero resistance from the
alternator case to the negative battery terminal. If the alternator case was painted or powder coated
it could cause a bad ground to the alternator mounting bracket which bolts to the to the engine and
a cable from the negative battery terminal goes to the engine block.

 

[RStovall]

It will only make the battery light come on if the plug is un done and the wire is powered

 

[ecss]

It will only make the battery light come on if the plug is un done and the wire is powered

Strange.

If you remove the 12 volts to the AC controller from the White wire does that
make any difference how the Brown wire works?

 

[RStovall]

As of right now that wire has no power whatsoever on it.

 

[ecss]

As of right now that wire has no power whatsoever on it.

Turn the ignition On.
Verify you have 12 volts at the gages fuse.
If you do, turn the ignition Off.
Remove the fuse.
Turn the ignition back on.
Apply power to the Brown wire.
Does the battery indicator light?

 

[RStovall]

Yes if I put power to it it lights, Gauge fuse is good

 

[RStovall]

Didnt change anything with or without fuse

 

[ecss]

Didnt change anything with or without fuse

First reseat the connector that goes to the Driver Information Center.

Turn the ignition on and ground the Brown wire. If the light comes on the problem is fixed.

If the battery light still doesn't work look at the light/socket where the battery indicator is
on the circuit board. Swap the bulb/socket with a different one.

The bulb has to pins. One pin goes to the Brown wire.
The other pin should have 12 volts on it from the gages fuse when the ignition is On from a Pink/Black
wire from the connector plug. (89 Schematic).

If you have an ohm meter you should have zero ohms from one of the bulb terminals to
the Brown wire.

You should have zero ohms resistance from the other bulb terminal to the gages fuse via the Pink/Black wire.

You need to find out where the circuit is open.

 

[ecss]

Here's a thread with the same problem you are having. In his case he bought a 87 and the
alternator wouldn't charge. No voltage on the Brown wire. The bulb and socket were missing.
He installed a bulb and socket and all was well.

 

[RStovall]

We tried all that and still nothing. We have no volts meter to read the voltage but on the wires I moved the lights around with ones I know come on and still nothing but I put power to the wire from the plus it lights up the light.

 

[ecss]

We tried all that and still nothing. We have no volts meter to read the voltage but on the wires I moved the lights around with ones I know come on and still nothing but I put power to the wire from the plus it lights up the light.

Has the alternator ever worked on this car?

What you did indicates you have an open circuit from the plus wire to the gages fuse.

If you look at the circuit trace on the flexible cable where you put power to it does the circuit trace
go to a Pink/Black wire on the connector that plugs into the DIC?

 

[RStovall]

I'll trace the wire n see an I bought the car drove it for a few days an it was great no problems then the heat an ac panel stoped workin we drove the car that day an some how we made it back home thank god but as it was sitting in the drive way running I saw the raido stop working an wasent long the car shut off jumped it off an would run as long as the battery was charged so I replaced the alt still no fix so I had it checked an it was good I replaced the battery checked all the ground looked all over the car but nothin is out of place an all looked to be working it did affect the light on the review mirror now with the switch on if u trun the light on it will make the chime noise come on but only once if u trun the key back of an on it will do it again idk if that has anything to do with it but I no it was working when I got it

 

[RStovall]

So the light doesent come on anymore on the mirror just that chime noise sounds

 

[ecss]

So the light doesent come on anymore on the mirror just that chime noise sounds

The chime going off is also an indication the gages fuse is blown or there is a wiring problem with
the gages fuse circuit.

I'll post in a minute what items use the gages fuse and you tell me what works and what doesn't.

It appears the person who sold you the car probably knew about the electrical problems. ad

 

[ecss]

Since I don't have the schematic for a 87 this is from a 89 schematic.

When the ignition is On the gages fuse provides 12 volts to the following items on a Pink/Black wire.

1) HVAC Programmer
2) HVAC Control Head
3) LH and RH vanity mirror light
4) Defogger relay
5) Courtesy Light Delay Timer
6) EGR Solenoid
7) Air diverter valve
8) Air select switching valve
9) Mirror header map light
10) Low coolant module
11) Chime module
12) Torque converter clutch and cruise Brake switch
13) DIC for the Battery indicator light
14) Vapor canister purge solenoid
You have said the mirror lights have a problem, the AC Control head has a problem.

Do the interior lights work?

Look at the egr solenoid.
It's located and bolted to a bracket on the front driver side of the engine that holds
the radiator water neck on the front of the intake manifold.

The solenoid has two vacuum hoses going to it and a two wire electrical plug going to it.

Remove the electrical plug.
Turn the ignition On.
You should measure 12 volts on the Pink/Black wire.

 

[RStovall]

yea I gess that guy really got one over on me its a nice car but this problem is insane I checked the pink an black wire goin to the ac panel it doesent have anything on it its on the c side of the plug number 2 wire

 

[RStovall]

The int lights do not work with the doors open I can push the button on the doors to make the lights come on an they work but if I do it by opening the door no an if I do it with just the headlight switch it doesent come on

 

[RStovall]

The pink an black wire on the egr plug has no power

 

[ecss]

The pink an black wire on the egr plug has no power

Are you positive you have 12 volts on the gages fuse in the fuse panel with the ignition On?