Problem...Solved

[lotusport]

I spent a joyous day at our fantastic new track east of Denver, High Plains Raceway | Your Colorado Performance Driving and Racing Future , just enjoying an open lapping day. Got down to some respectable times and embarrassed a number of Porsches and Vettes, so it was a good day. Even felt as if I've learned the track fairly well...got good repeatable laps and times (maybe repeating the same mistakes on a couple of turns, but I did learn).

Drove out of the track at the end of the afternoon session, everything running like clockwork, and about a mile down the road the battery charge light went on. Oh, #e!!, I thought I might have tossed the belt -- no, the belt was in place and driving nicely, thank you.

Then thought the alternator had failed (wouldn't be the first, hmmm?), but thought I might be lucky enough to make the ~50 miles of mostly Interstate to get home on the battery.

Got home, checked all the electricals and everything was working fine. Put a meter on the battery and got 12.8 volts with everything off, sooo...scratched my head and drove to dinner with some friends (did I mention that we have had a phenomenal four days of excellent weather in Denver?); drove home with headlights, radio, heater fan, V1, all operating and not a hint of trouble -- but that d@mn red light on the dash was burning brightly!

Later, got the inspiration to RTFM and found (page 137) that there's a fuse entitled "Alternator Sense" in the engine bay fuse box on the firewall to the left, near the ECU -- it's the one with the red insulator on the wires running to it. Fuse blown. Replaced fuse. Popped as I pushed the replacement home. So it was hot with everything turned off.

OK, so there must be a wire somewhere that sends a signal or carries a current to this fuse. And it was definitely shorted. Looked over to where the alternator resides in its new position after SC installation and there is a cloth tape-wrapped wire that was resting on a sharp edge of a cooling slot on the alternator. Wire had a little shiny spot that had rubbed and exposed the wire. Dead short. This is the sensor wire (see pic with a little Gorilla Tape wrapped on the wire -- quick temporary fix, along with a small piece of G-tape on the sharp edge of the cooling slot.

Replaced fuse. No spark. Started car, battery charge light went out. Problem solved. Next, I'll put some more permanent insulation on that wire and a tie wrap that will hold it clear of the alternator. Yeehaa, on the road again... Hope this will help the next person who gets a charge light.

[TheViper]

Bob,
That fuse, R3, is in the circuit that senses the differential voltage between the alternator and the battery. If 12V is flowing on both sides, they cancel each other out and the warning lamp stays off. If there is 12V on only one side the light comes on as you found. You can demonstrate this by turning on the ignition but not starting the engine, the warning lamp will illuminate.
Michael

[LesleyHenley]

Very useful information.Thanks a lot.


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