View Full Version : Alternator control problem - 1990 Celica GT

05-15-2014, 08:52 PM
Hi, I was wondering what the specs are for the battery warning light diode in a 1990 Toyota Celica GT, as described in: EDIT: I HAVEN'T BEEN A MEMBER LONG ENOUGH TO POST LINKS

Screenshot from 2014-05-14 22:22:46.png

I seem to have the same problem, and don't know what kind of replacement I should order (probably from Digi-key, as replacement OEM parts seem impossible to find). Or if you know somewhere I can order an actual replacement? For that matter, I don't know for sure where to even find that diode, as I've taken apart my interior except for the instrument panel, since I drive it to work daily...

Measured the output of all 3 pins connecting to the voltage regulator on the alternator, all measure 12.xx volts. This points to a fried battery warning light diode, as that website indicated.

The battery discharge light NEVER comes on, not even with the engine off and ignition on.

The alternator puts out no power under any circumstances.

For the last couple months it was charging irregularly, and the battery warning light was always on. The battery voltage would be swinging from 10V all the way up to 18V, so I replaced the voltage regulator. Shortly after doing so, I shorted the alternator while checking bolt tightness before I started the car, but nothing seemed wrong and the battery warning light wasn't on, so I assumed it was fine. However, the alternator no longer works at all.

The main ALT 100A fuse is fine, as in the 40A AM1 fuse, and the 7.5A IGN fuse.

If anyone could tell me anything about this problem I'd be very grateful!

Sorry for the double post, but the Forum: Electrical, Audio & Security seems to be dead

05-17-2014, 03:55 AM
It isn't dead. You made both posts on the same day expecting an immediate answer. A little patience goes a long way bud. ;)

Sounds like you have been checking the correct areas to try and track things down. If the alternator is dead, you will need another. The good news is that you can pick one up pretty cheaply.
The diode in the dash, you can test with a multimeter and verify if it is bad or not. I would do that first.
You can google for the proper testing procedure for Diodes.

All the best.