FJ62 - Alternator output 14.7 not connected, 12.6 con, cooling fan activated by removal of Alt Cable (1 Viewer)

[indy500driver]

Hello mudders,

I am hoping that I can rely on the mud heads for some troubleshooting. I have a 1989 FJ62. I got the truck a month or so ago. The truck has some charging issues. I think there is a frozen relay, short, broken or dirty connection somewhere. I put in a new alternator but getting weird readings.

I added a jumper cable from the alternator post directly to the + terminal on the battery and still 12.6 reads. On a hunch, I decided to remove the stock alternator cable from the + post and just use the jumper I made with a 100 AMP circuit breaker that is attached to the + post. Start the truck and still 12.6 at the + post. I then attach the meter to the cable side on the CB, and open the circuit ..... and SURE AS s***..... the jumper reads 14.7... So I then move the meter to the stock alternator cable, and 14.7.

So when the jumper cable and the stock Alt cable are OFF the +post and not connected to anything I get solid 14.7 Volts out of the alternator. When i connect either one to the battery + it immediately kills the charging and drops the reading back to 12.6 which is just the battery reading.

Important note... When I REMOVE the jumper or the stock alt cable.. the cooling fan turns on.. and when i put it back on the + terminal, it turns off. Literally thought it was just a coincidence first time but then i tapped it on/off a couple times and the fan is definitely being activated by removing the Alt cable from the + terminal.

SO im guessing its the charge light relay or cooling fan relay thats frozen, a broken connection in the charge circuit or a dirty connection that is causing rerouting of power or its just some asshat PO that screwed it all up... or a combo of all the above.

Please help brothers (and ladies too)

Thanks,
Dom

 

[Output Shaft]

Be careful fiddling around with the alternator. Never disconnect it from the battery while it's charging.

At this point, I would remove the alternator and take it to a shop for them to test the output. You might be seeing 14.7 volts on a meter, but there may be no current behind it... that would explain why you're still seeing 12.6V at the battery.

Once you know the alt is good, check the fusible link carefully at the battery. Look for burned and corroded contacts or a burnt wire.

Hook it all back up like it should normally be when you've verified the alt is good (without a circuit breaker spliced inline to be he batt) and see what happens.

Never place a CB between the alt output and the battery. That's probably the best way to fry an alternator. If the CB trips while the engine is running, bye bye alternator.

 

[indy500driver]

Any thoughts on the cooling fan activation by removing the alternator cable? I will hook up an ammeter to see if I have current at 14.7. I actually replaced the Fusible Links already because all the wire insulation was dry rotted, there are no burns or melted wires at the battery + post.

I actually got the idea about the CB from Tony Candela who is behind 150 Amp Alternator Installation Kits – CE Auto Electric Supply . He sells an alternator install kit with integrated fuse. I just decided to use a CB instead of a fuse. And I am using stock output 80 AMPS

 

[tmxmotorsports]

With everything hooked up like factory start the truck and then disconnect the positive battery terminal and if the truck dies the alternator isn't charging as far as the cooling fan I really don't know maybe its tied into the alternator wire some how that when you disconnect the wire the circuit thinks the truck is off just a wild guess.

 

[LAMBCRUSHER]

cooling fan relay thinks the car just turned off when 14.7 turns to 12.6...might be a bad charge light bulb. have you seen it come on when the key is on but car is off?

 

[indy500driver]

Thanks @tmxmotorsports and @LAMBCRUSHER for responding.

I just started it up and let it warm up. I took a video of what happens because that's easier for you all to see and hear.

Also based on your responses... Is the cooling fan actually the engine bay vented fan on the left side of the engine bay that comes on after the car is off? If so then maybe I'm naming parts incorrectly, and apologies for that. The fan that starts blowing appears to be the engine/radiator fan.

Here's the video..

 

[tmxmotorsports]

Yes the fan that we are talking about is on the drivers side inner fender.the engine cooling fan isn't electric it is manual driven by the engine . it sounded like when you disconnect the alternator the engine speed up making the mechanical fan speed up. did you try the method that I mentioned leave the circuit breaker on and remove the positive battery terminal while it's running if the engine dies the alternator isn't charging. when you disconnect the alternator via the breaker the alternator doesn't see a load when you hook it back up it does. how old is your battery it may be bad.

 

[Output Shaft]

Here's a start

 

[tmxmotorsports]

Or just take the battery out and the alternator out and have them both tested. It really seems to me it's your battery tho.