I had another thread about trying to learn about the operations of the exciter. While related, I think a new thread specific to diagnosis is prudent.
It’s a 1993 Mercedes 300SD. Has lots of modules with issues, but car fundamentally operates properly, and the engine, transmission, and brakes are perfect (primary reason why I bought the car).
The alternator bulb checks out perfect, 9 ohms like all the other cluster warning bulbs. It just never turns on.
When I check the bulb socket, key on, I get voltage on both sides. Around 8-11v on the one side, and 12+V on the other.
I do not get any parasitics through the battery and D+ cable combo per my clamp on meter.
If I disconnect D+ at the alternator and ground it, I don’t get the light to illuminate.
If I start the car, and idle it, I am discharging the battery. Once I take the engine over 2500RPM it self excites and gives me 14.3V.
Never under any circumstance does the bulb illuminate. But again, I see voltage at the terminals.
So what’s the best bet to start?
I was thinking step 1 is to do the following:
Start the car, verify no current flowing on D+ or B+. Verify voltage at B+. Use test light between B+ and D+ stud, verify that this excites the alternator.
What else should I be testing and checking to start to track this down?
Thanks!
It’s a 1993 Mercedes 300SD. Has lots of modules with issues, but car fundamentally operates properly, and the engine, transmission, and brakes are perfect (primary reason why I bought the car).
The alternator bulb checks out perfect, 9 ohms like all the other cluster warning bulbs. It just never turns on.
When I check the bulb socket, key on, I get voltage on both sides. Around 8-11v on the one side, and 12+V on the other.
I do not get any parasitics through the battery and D+ cable combo per my clamp on meter.
If I disconnect D+ at the alternator and ground it, I don’t get the light to illuminate.
If I start the car, and idle it, I am discharging the battery. Once I take the engine over 2500RPM it self excites and gives me 14.3V.
Never under any circumstance does the bulb illuminate. But again, I see voltage at the terminals.
So what’s the best bet to start?
I was thinking step 1 is to do the following:
Start the car, verify no current flowing on D+ or B+. Verify voltage at B+. Use test light between B+ and D+ stud, verify that this excites the alternator.
What else should I be testing and checking to start to track this down?
Thanks!