Beaniam

22re 93 pickup.
Yesterday went out to start the truck and the brake/battery light come on. Check the battery terminals and I'm at 12.5V so I figure another alternator has crapped out. Hop back in the truck to move it and the lights start to flicker and then go out. Drive for about an hour with no more charging issues. Shut the truck off for about half an hour, start again and the lights stay on for about 5 minutes. They then go off again and stay off for the hour ride home. After getting home I swap out the alternator with a used one I had laying around. Start it up, no charging issues. This morning I start the truck and the lights flicker for about 5 seconds then go off.

The fact that once they go out and NEVER come back on while the truck is running is kinda making it hard to troubleshoot. Seems to only happen on cold starts. I'm guessing the internal voltage regulator in the alt but my spare didn't have that problem when I last used it. I guess I'll pick up another alternator today and see what happens.

Grounds and wires look good, feel tight. I've always kept dielectric grease on the alternator plug too to keep corrosion out.

swampfox

you might check the alt belt to see if it is worn out. it may be slipping until it warms up. also you might look at the 7.5 amp fuse in the fuse box next to the battery .it may not be getting a good connection.

Beaniam

Changed the alternator, changed the belt, replaced the main + line from the battery + to the relay box under the hood, replace a body ground, checked the oval harness on the alternator no frays or burns. Started and batt/brake light flickered for about 2 seconds. Could hear engine speed drop slightly when they went out like the alternator just put a load on it. Once they go out I can shut off and start the truck all I want and they stay off. Only seems to do it cold.
Only thing I haven't done yet is run a line from battery + to alternator hot post. Big 3 mod I suppose. After that I guess all that's left is rip out the entire alternator wiring harness and start examining it. ugh

Beaniam

What tells the alternator to start charging? Was looking through the FSM and not having an easy time trying to figure it out.

milehigheric

A sense wire from the ignition. The easiest way to test it is to turn your key to 'on'. If your battery light is on your dash then the sense wire is good. There is still a chance the wire may be damaged between the dash and alternator however, so a voltage check of the wire at the alternator would be a good idea.

Beaniam

Yes always have a solid steady battery light with the "on" position. Flickering doesn't start until the engine is running.

Stuwy123

iTrader: (1)

There are two grounds to your frame.
One on either side of the motor.
I think you said you checked/replaced one but not the other?

abecedarian

Dielectric grease on the connector? Do you know that it is an insulator? Try cleaning the grease off and see how it goes.

Bridger5228

My 90 'runner would do this too. Both the brake and batt lights would come on and go off 2gether, yet my alternator was charging just fine. Kinda weird...

Beaniam

I've always done this to keep water corrosion out. I'll clean it out though to try. I looked up the charge light indicator, $88 dealer part but what exactly is this? An expensive light bulb, a diode or a relay?

Beaniam

Replaced the ground connectors, battery terminals, starter and alternator terminals, and added a 4 gauge fused line from the battery to the alternator. So far no more lights flickering at me.