Low Voltage Idiot Light

Sid Lambert · #1 11-09-2008, 05:34 PM

I'm trying to diagnose a strange electrical issue on my RV-4.

If I turn off the bat and alt master, the radios will stay on until the engine quits. So the system is is running from the alternator. It works normal if the engine is not running.

I have a sneaking suspicion that it has to do with the idiot light wiring. Voltage going back through the light to the main bus. 1.6V when the engine is not running.

My question is... When wiring an idiot light from the L lead on the alternator do I need to put a diode between the light and the 12V + bus? Or am I barking up the wrong tree?

I know I should be using a nifty low/high voltage system. I will probably replace the radios and a few clocks along with the charging system later but this is what I have now.

vic syracuse · #2 11-10-2008, 07:02 AM

Hello, Sid. You could have one of a couple of issues here. My suspicion is that your alternator field is wired hot, and the alternator output is wired to the bus on the bus side of the battery contactor. Thus, the alternator continues to produce until the rotation is stopped. Do you have a separate field switch? If so, you could check by either pulling the breaker or opening the switch for the field. The laternator should stop. If you don't have a field switch or breaker, then I think someone might have wired it continuously hot.
If so, I would recommend that you do wire a field switch, as the scenario you describe would not allow you to kill the alternator in flight, unless you have a large alternator circuit breaker that you can get to.

Vic

Sid Lambert · #3 11-10-2008, 07:50 AM

It does have a switched field. It originates on the main bus after the main contactor. The B lead runs to the bus at the same spot. It does have a breaker on the panel that I pulled so I could reset my GPS. I think I load dumped the system and popped the VR in the alt.

At any note... I ordered a non-regulated alternator* and I'm about to drive down to ACS to pick up a nifty LR3C. I can't stand for things not to work as designed and this puts me in compliance with Bob Nuckolls now.

* It's from a 1982 Ford Courrier 2.3l if anyone cares. Napa # RAY138191