1991 3g alternator not charging

[BigShowJoe]

1991 LX hatch with F.A.S.T ECU, MSD ignition and distributor, HCI, Vortech V1.

The original 75 amp 2g alternator quit charging and I took the opportunity to upgrade to a 3g 130 amp kit from LMR.

Got everything installed and wired without using the original black/orange power wires, and I get no charge with the engine running. I verified continuity from the alternator post with the new 4 gauge power wire back to the battery positive terminal. I have 12v constant on the yellow wire. The white wire is connected from the middle of the D plug to the stator plug as it should be. The green/red wire is suspect though. With the key off, it has 0 volts which is expected. With the key on but engine stopped, it has 12v, also as expected. The strange thing is that with the engine running and D plug disconnected from the alternator, that green/red wire is fluctuating in volgate. Never below 12v but my meter reads 12v, 16v, 14v, and even a spike to 20v for a moment.

I can only assume that is the reason behind no charge from the alternator since that wire doesn't have constant voltage but I need input from you all. What can cause voltage on that green/red wire to jump around like that? Failing ignition switch sending power through that bulb/resistor circuit?

 

[AeroCoupe]

Have you verified that the alternator is good?

 

[BigShowJoe]

Yes. This is actually the second one I've tried. Before I found this fluctuating voltage I was fairly sure I had a bad alternator out of the box and even LMR agreed so they sent another one.

 

[AeroCoupe]

So you have had it tested and it’s good. I would continue with the investigation on the green/red wire. Post #2 in this thread:

Alternator Charging Issues Green Wire Red Stripe

stillchasing my tail here. Can anyone tell me what this blue connector is and if they go bad? It connects the green wire with red stripe from dash to alternator voltage regulator. Narrowing down to a short on this end of the wire possibly

stangnet.com

 

[BigShowJoe]

So you have had it tested and it’s good. I would continue with the investigation on the green/red wire. Post #2 in this thread:

Alternator Charging Issues Green Wire Red Stripe

stillchasing my tail here. Can anyone tell me what this blue connector is and if they go bad? It connects the green wire with red stripe from dash to alternator voltage regulator. Narrowing down to a short on this end of the wire possibly

stangnet.com

Yeah the only thing that doesn't add up for my case is that fluctuating voltage on the green/red wire only with the engine running. If only I knew what may cause that.

 

[qikgts]

What/where do you have the green/red hooked up to?

 

[BigShowJoe]

What/where do you have the green/red hooked up to?

It's still coming out of the factory harness and spliced into a new D plug that came with the SVE alternator kit. I get that voltage with the D plug disconnected from the alternator. O volts with key off. 12 volts with key on. 12 then 16 then 14 then 20 then 12 again and repeat while the engine is running.

 

[qikgts]

Have you changed battery light bulb in the cluster to an LED?

 

[BigShowJoe]

Have you changed battery light bulb in the cluster to an LED?

No.

 

[qikgts]

Have you disconnected the g/r wire from the factory harness and given it ignition 12v on the alt side from another source (like + on the coil factory wiring) to verify the alt charges?

 

[BigShowJoe]

Have you disconnected the g/r wire from the factory harness and given it ignition 12v on the alt side from another source (like + on the coil factory wiring) to verify the alt charges?

No but my MSD coil is on the same side so it should be an easy test. Do I need to put a resistor in that?

 

[qikgts]

No resistor needed to test.

 

[BigShowJoe]

No resistor needed to test.

Ok I'll try that. I did try connecting the green/red wire out of the D plug directly to the alternator post with the power wire but that also got me nothing.

 

[qikgts]

If you were connecting the g/r on the alt side to the + post that should have done basically the same thing. Maybe you have a bad connection/connector in the alt plug. I've seen dumb stuff in aftermarket harnesses before like wires that weren't stripped back when they were crimped.

 

[BigShowJoe]

If you were connecting the g/r on the alt side to the + post that should have done basically the same thing. Maybe you have a bad connection/connector in the alt plug.

I can get readings from the plug with my volt meter probe in each of the three pins. That's how I noted all the voltages.
If you're talking about the alternator itself, this is the second one I've tried.

 

[qikgts]

Just to be sure...

Of course we can ignore the fusible links as you've got a big fuse in there with the kit.

 

[BigShowJoe]

Just to be sure...

My red is a single and goes to the starter solenoid but has continuity and I have 12v at the alt post. Other than that mine is wired just like that diagram.

 

[qikgts]

Only other thing I can think of would be no ground to the alt itself. That's all I got.

 

[BigShowJoe]

Only other thing I can think of would be no ground to the alt itself. That's all I got.

I know. It's a mystery for sure. Definitely got good ground because I tested between the alt case and the engine ground strap with my volt meter beep setting.

 

[qikgts]

That is just measuring continuity. In other words, when it beeps thats just a verification there is a connection of "some kind". It won't tell you how much current it can handle. Ohm measurement would be better. Voltage drop test is best.

Jumping a decent size piece of wire between the alt case and block, chassis, (so long as both of them are grounded properly) or neg side of the battery should work for test purposes too.

Gotta be something silly going on. You'll find it.