I have a 79 supercab with. 429/ 3G alt.

I have put over 6000 km's on without a problem. Yesterday I was driving and my stereo turned off, on, off. Then my lights started flickering, the fasten belts light came on, and I pulled over. I was on a major time crunch and had little time to waste. I grabbed my meter and I only had 11.7 volts. I grabbed a new alt at Napa and quickly swapped it out. No change. Traced all wires and everything looked good. So I swore a few times, went into Napa and had them test the alternators, they checked out good. I couldn't waste anymore time so I bought a new battery and drove home.

After playing with it at home everything looked good. I had a questionable connector coming from the Green/Red wire so I cut it off. When I touch the wires together with the engine running, I get a voltage spike from 12-13.8 and then it slowing declines back to 12. If I pull the wires apart and touch them together it does the same thing. It spikes but won't stay charging.

Any ideas? Is the Green/Red stripe wire run to the ignition?

 

Why'd you do the 3G swap? because you read it on here? or did you actually need it?

 

I upgraded the wiring harness, put in better bulbs, have 2 amps with some high dollar speakers, Mark IV fan, electric heated seats, etc. It was needed. It also has a secondary painless 7 circuit boss for aftermarket electronics.

 

This whole thread is pretty vague.

Measured where?

Can you explain this more?

What wires? And again, what voltage specifically are you measuring?

GREEN with RED stripe is hot-in-RUN to the original voltage regulator. It's re-used for the 3G setup.

 

The bad connector was the bullet on the green/red stripe. I eliminated the connector. While the truck is running, I re connected the green/red stripe and the voltage spikes then drops.

I am measuring the output of the alternator.

 

The GREEN with RED stripe wire needs to run to the 'I' terminal of the alternator through the parallel combination of an ALT light and shunt resistor.

Is the small wire from the base of the alternator to the 'S' terminal installed? It almost sounds like the alternator is falling offline after it excites.

 

When I installed the alternator I used the Painless 3G kit. The plug for it has the wires color coded to match the truck wires. There is a green/red stripe wire coming from plug on alternator, which I attached to same on truck harness that went to stock alt.

I do not have a resistor on it, there was never one on the truck when I got it.

And it is doing exactly like you say, falling offline. It has worked fine all year up to now.

I pulled the grounds off and cleaned and checked them.

 

If you have an ALT light, the resistor is already on the back of the instrument cluster.

Have you verified the connection to the 'S' terminal of the alternator as I described in my previous post?

 

My truck has a volt gauge, not light.

I'm not sure what you mean by "S" terminal. On the 3G alternator there is only 3 wires coming from the plug.

Black/white wire which goes to small plug back on alternator.

Yellow to positive power

The green/red stripe from 3G plug to same on harness.

The heavier gauge wire is hooked through the mega fuse, checks out fine.

Grounds good.

 

Here is the kit I used, I've installed this 3G kit on 2 of my vehicles and they have worked flawlessly until now.

Part# 30831 Details | Painless Performance

I am not great with electrical but know the basics. From what I can see something is interrupting the trigger signal to start the alternator.

 

That's the one I'm talking about. The back of the plug should have the letter 'S' molded onto it, which represents the stator. Pull the 3-terminal plug off, and disconnect the short WHITE with BLACK stripe jumper wire from the alternator. Verify continuity between the end of the jumper terminal and the terminal corresponding to the 'S' position in the 3-terminal plug.

Next, turn the key to RUN. Verify the connectors in the 3-terminal plug corresponding to 'I' and 'A' have 12 volts.

If your 3-terminal plug is not labelled, the terminals are colored as follows:
I: GREEN with RED stripe
S: WHITE with BLACK stripe
A: YELLOW