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Discussion Starter #1
201616
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I bought an 02 ccsb 7.3 less than 2yrs ago and the charge light was on when I got it. Previous owner replaced alternator and both batteries. I figured I'd get around to figuring out why the idiot light was on. Well, the alternator finally quit charging this week. I replaced it; no luck. Turns out the 'I' circuit (idiot light) is supplying voltage correctly, but the 'A' circuit is not. Traced the wire hoping to find a broken fusible link but only got as far as where the alternator wiring all branches off from a large connector over the valve cover, under the turbo pipe. Specifically, under the flex hose connecting two hard pipes. Well the wiring harness has been rubbing up against that flex hose and a few wires are left exposed. I don't really understand why it's pushed up against the hose. Seems almost bent upward. If it were tied down I don't think it would have become an issue. You can see unwrapped wires in the photo, but the wires actually touching the turbo pipe are rubbed bare to the copper wire.
Is there a trick to how it should be routed? I've temporarily jumpered the 'A' circuit to the positive terminal of the driver's side battery so it's at least charging, but my long term options seem to be to repair or replace the harness on the top of the motor. Not sure which exact part that is but preliminary googling suggests it's around $600 :O I guess I don't really have a question exactly, but if anyone has a suggestion on how to proceed, I'm happy to try it.
I'm even open to bypassing that harness. I think the 'I' circuit could be tapped in where the dual alternator jumper sits near the passenger side battery; the 'A' circuit straight to the battery +; the B+ wire too. (Yes I'd fuse each.)
But the harness in the pics has a lot more in it than just the alternator wires. I need to prevent it from rubbing.
 

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I just replaced my alternator and the idiot light stays on. I don't know yet what is the problem. Alternate gauges and a separate multimeter confirm the alternator is charging.

I'll share this with you. Hope it helps.
201626
 

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Discussion Starter #3 (Edited)
Thanks.
I've read a few articles on testing alternators, and one thing that pops up often is checking voltage drop. If there's excess resistance due to bad connections, voltage can flow through the idiot light, or maybe current can be wasted causing excess load on the alternator causing it to fail prematurely. If you test the voltage between the stator (O/LB) and the battery's positive terminal, (engine running) you'd expect no difference. They should both be around 14v. But if there's resistance in that wire, which there was in my case because of it being rubbed on the intake tube, then there will be a voltage drop that should register on your meter. (Google to see what's reasonable and what's not. I think it was anything over 0.2v was not good.) For awhile I've had my idiot light on, though the alternator was charging. I didn't perform the test I just described, because my alternator died before I got around to it. :) After I replaced the alternator, the idiot light still stayed on. Once I found my rubbed-raw harness, I jumped that O/LB connection straight to the battery positive terminal, and my alternator charges fine, AND my light is now off when the engine is running. (NOT a permanent solution -- This wire needs to be fused. But I'll probably leave it this way until I can get the harness out for repair.)
I would expect you could also confirm this as the problem by testing the resistance (engine off, C185 disconnected) from C185's O/LB pin and the battery + terminal. It should be pretty close to zero. If it isn't and you find no damage to the harness, check the 'jumper' plug. (Though I think only the idiot light wire goes through it.) That harness is right behind the passenger battery high on the fender. Easily seen from above and has a single wire coming out of the front side doing a U-turn back to itself. Mine had a little corrosion inside so I cleaned it too.
 

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Discussion Starter #4
Here are some additional pages from the service manual. This is for a 99 F series. You might find some of the troubleshooting steps useful.
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Thank you! We seem to have the same book!

As I said, my alternator is brand new - about two days old. However, the Highway is calling (motorcycle) so I'll have to check it out when I come back. :D
 
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