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Alternator not charging.

WLDSTALLION

Newbie
Joined
Jun 7, 2010
Messages
28
So I stumped on this. I have a 97 explorer motor (with the 4G alternator) with the RJM harness and A9L computer. It stopped charging so I got a new alternator from the Auto store, that didn't change anything. I can unhook the signal wire from the RJM harness and touch it to 12v and it starts charging, with the old and new alternator. So I assuming my computer is not sending 12v signal, i confirmed this with my multi meter. Also my check engine light has been on around the same timeline that it stopped charging. I pulled the Koeo codes and I am only getting 81,82,84,85, which are not related.
I am not sure where the signal wire comes from? I cannot find it on a pin-out of the computer.
Who can check out my A9L, preferably with a quick turn around time?
 

904Bronco

Contributor
Bronco Guru
Joined
Sep 28, 2004
Messages
5,334
Loc.
San Martin, CA
Generally, the signal to charge comes from the chassis harness, as in key in run mode. Not from the ECU.
What chassis harness do you have? Fuses to check, I think. Factory harness had green wire with a red strip...
 

Broncobowsher

Contributor
Total hack
Joined
Jun 4, 2002
Messages
33,325
Alternator is not ECU controlled. Don't know the RJM harness to know where the alternator turn on power comes from. I would start by checking the fuses.
 

904Bronco

Contributor
Bronco Guru
Joined
Sep 28, 2004
Messages
5,334
Loc.
San Martin, CA
"#26 is ignition power wire for your alternator. It is not meant to charge the vehicle, but to turn the alternator ON when you turn the key to RUN. Consult your alternator installation manual for further instructions."

Just looked at the install instructions, this is about it for information provided.
Even in the break down of fuses and relays there is no mention on where the Ign feed comes from for the Alt in their system.
 

Broncobowsher

Contributor
Total hack
Joined
Jun 4, 2002
Messages
33,325
Forgot about that little light bulb that was buried in some harnesses. Not sure if the RJM did that as well? Pretty sure the Ford Motorsports did that. The resistor should keep the circuit alive if the light bulb burns out, if it is there.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
43,498
Because it sounds like everything else works, then your ignition switch and wiring to the relays are still good. So the fault lies either in the relay, the socket or the wire specifically for the alternator.
I don't know where they were spliced inside the harness tape, but you should still be able to test a few things.

First is to check the four fuses. Second is to swap the relays.
Or just put a new one in the place of the old one, since having spare fuses and relays around is a good thing no matter what.
Make sure to mark the one you take out once you confirm it's good or bad.

If the fuses are good and swapping/replacing the O2 relay does not fix the problem, then test the circuit somehow using other methods.
If you can apply 12v directly to the output contact in the relay socket (the one facing different from the other three) you should energize the Green w/red wire and the alternator.

As you figured, you just have to get power coming back on to that wire and you should be good to go.
With a spare alternator!:D

Paul
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
43,498
Great. Congrats! Glad it was a simple fix.
And thanks for letting us know.
 
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