Electrical Problem Solving - 02/18/2018
Now that the car is running, it's time to figure out why the alternator doesn't work. I figured "bad alternator" and bought a new one. Turned out to be a special order part and cost me $120. With a little more investigation, the charge indicator lamp in the dash never comes on under any circumstances. I ground the brown wire out at the alternator side and it doesn't light. I measured the resistance of the L terminal at the alternator to ground and it measures 600 ohm with the car off. This seems to be a little high as the terminal should be close to ground as it has to pull 250mA through the bulb and 600 ohms is going to pull less than 1/10 that and I doubt the bulb will ever light up at 20mA. The factory service literature for the CS130 doesn't mention this situation and no one else seems to have experienced something similar either. So time for an investigation!
So the dash bulb doesn't work. Rather than dig into the dash just yet, let's see if we can get the alternator to run directly off of a bulb and socket. Hard to tell in the photo but it does light the bulb.
So that stinks. Dash has to come off to get the stupid bulbs out.
Removing sockets to test bulbs since none of them light and... every single one is bad. Not the bulbs, the sockets. The brass tabs snap off every single one. Well that's sucky.
So using test bulbs and alligator clips, I test to verify the circuitry in the engine compartment is good or bad. This tells me if I have to deal with pulling the engine harness or dash harness.
It's getting kinda crazy in here. Everything checks out though, which is good.
Order a bunch of new sockets since all GM cars of this era back to the late '60s used them.
Woohoo. Lights! Bulbs and sockets are now fixed.
By jumping it and bypassing the sense wire it works... so something is wrong from the alternator wire back to the dash wiring...
Checking the oil pressure idiot light since it still doesn't come on. It works when it's grounded, so the sensor appears to be bad.
New oil pressure sensor...
...and it works. No charge light still...
So it's time to locate the sense wire from the alternator back to the firewall. It's brown. Hmm...
Gee... it's been cut and spliced.
It was spliced into the EGR solenoid feed. I guess the lamp in the dash died and rather than fix it, someone decided to splice a switched +12V onto it. Kind of a terrible way to do it...
Looking at the factory service manual, there should be a diode in series with the alternator. Check it out and find... it's blown apart...
Cleaning it all up to get it ready for whatever is next.
If I jump it all, the alternator charges and the light comes on. Great!
Solder the cut wire back together and add a 1N1001 diode in series in the bad section, cover it all up with heat shrink.
Idiot light now works as it should.
And the alternator works when it's all hooked up! Now I can put the dash back together finally...
My woes weren't over as the remanufactured alternator I had purchased ended up being bad out of the box. I had to troubleshoot it for 6 hours to determine that, and then the parts store manager accused me of lying and re-tested it 3 times on their new test stand (failing all the while), then denied me a refund, but that's a story for another time... On a side note, I am really good at taking this engine's accessories off and back on in record time. And cleaning all of the little piece so they aren't filthy for next time.
Return to 1989 Cadillac Brougham
Last updated August 23rd, 2018