I was chasing down a ECU fault code last night and end up blowing the Ecu fuse inside the car. I put in a new fuse this morning and now the Battery light stays on!!

I've checked the battery with a volt meter while it's running.

14.3 volts running with no load.
13.6 volts running with everything on in the car.
12.3 volts with car off.

Is it possible that when I grounded out a sensor wire and blew the ECU fuse that it blew a diode in the alternator?

The car runs fine, no flickering of the lights or dimming.

 

Unplug the plug with small wires from the alternator. Then turn the key on (no need to start); the battery light should stay off. If it doesn't there's probably a short in the wiring somewhere between the alternator plug and the light. I assume this is a swap job so check where splices were made. If it does stay out the alternator is at fault since it is working but it also controls the light.

It's also possible the alternator is not getting power on the IG wire in the small plug but it is still managing to charge the battery somehow. Make sure all the fuses are still good.

 

I took the plug off and the light stays out.
I get power on two wires at the alternator plug. both have the same voltage but when I hook up a test light to the 2 wires, 1wire lights up the test light bright and the other wire the test light is dim but both wires show the same voltage.
If a diode goes bad would this cause this problem?

 

Probably the regulator unit in the alternator. It may be hard to buy seperately. A bad diode causes low output and possibly the light coming on. Either way the cure is the same, swap out the alternator.

 

I put another alternator ("used Mitsubishi") in and solved the problem. I got a regulator and diode pack from a "Honda" remanufactured Accord alternator that I'm going to ut in the old alternator to find Out what exactly went bad in it.
I looked on a alternator rebuild site and it said most likely the diode pack was bad according to the symptoms I had.

This alternator (Mitsubishi) puts out 14.4 volts with no load and 13.98+ with a full load.

Thanks for the Info "mk378" !!