'94 B4000 Battery Light On

[Steve777]

Noticed the battery light on while driving today; made it home OK and then started checking the battery voltage. About 12v with the engine off; drop to 11.7v or so at idle and does not get any better if the engine is rev's up. Battery charges up just fine on an AC charger (which I am doing now).

So normally I'd assume its the alternator, but before I rush out to buy a new one I thought I should check the fusible links (which I assume this car has). I don't have a wiring diagram, but I would guess there are two links, a big one on the main power line and a smaller one on the voltage sensing line to the alt. I was looking for an easy way to test if these are good without digging around the wiring harnesses, and had a couple of thoughts:

On the big one, I would assume if there is batt voltage at the big terminal on the alt then its fusible link is good. Same with the sensing wire, but probably have to have the ign on and maybe the engine running to see voltage there.

Does this plan sound right? Any other ideas? Or does someone know where these fusible links are?

TIA

 

[RonD]

Key OFF
The B+ wire on alternator, stud/nut terminal, should have battery volts, if fuses are OK

Unplug the 3 wire connector on alternator
Yellow wire should have Battery volts if fuses are OK

Green wire 0 volts
Turn on key
Green wire should now have battery volts, just slightly less is OK, because key is on now, this is Battery Light wire, just FYI

Make sure short white jumper wire is plugged into alternator

If these 3 wires test OK, and engine running battery volts are less than 13.5volts then replace alternator

 

[Steve777]

Thanks RonD!

Yellow and green wires work as you say they should. So likely fusible links are fine. Not sure what you mean by the "short white jumper wire". There is a white and black wire in the center position between the yellow and green. And there is white and black wire in a separate connector further down, that I see. Did you mean one of these, or is there another white wire supposed to be there, somewhere?

Unless there is a missing white wire somewhere else, I think I've convinced myself that the fusible links are good, so it is most likely new alt time...

 

[RonD]

It is the same wire, white/black, just a jumper wire that connects Voltage regulator(3 wire connector) to the Stator inside alternator, single spade terminal

 

[Steve777]

OK. New alternator it is. Thanks again.