Intermittent Alternator Light Options

[yeahmag]

Got a strange one... Alternator light started flickering on my way to this weekends autocross. This was on the highway at steady rpm of around 4K. I hadn't seen it flicker like this before: sometimes on dim, sometimes on for a few seconds at a time, sometimes flickering.

I figured I'd just carry on and hope I could make it through the event. As I pulled off the freeway on to surface streets the light went off and didn't come back on for the duration of the event. Packed up and headed home and only had a brief flicker or two while on the highway. I've never seen it come on while on surface streets or at idle.

I figured I'd check the alternator for AC voltage (failed diode) and maybe change the belt (which I personally run on the loose side and is probably aging out). Anything else I should look for? Almost feels like a marginal VR, but I've never had one fail in this way.

Thanks!

-Aaron

[Spoke]

You could run some simple tests with engine running about 2k RPM.

On the alternator connector on the relay board, measure:

D+ to chassis ground (not the engine); should be the same as the battery
DF to chassis ground; should be 5-10V
D- to chassis ground; should be 0V
Battery POS to chassis ground

The voltages will let you know how well the battery, alternator, and wiring is doing.