It sounds like that is the charge light. I have not seen a yellow one, but it could be faded or have been replaced. IIRC, one side ends up at the brown wire on the small terminal on the Renault-style alternator. The other side is a blue wire from the fuse block.
What Denny says is true, the first thing I would do is check voltage from the master switch to ground. You should be getting 14+ volts when the battery is getting charged. Not sure at what point the light is supposed to come on, but if it is flickering, it's probably a weak alternator...

Ironically, of the two cars, that's the one that will abide having the master switch left on for a week and still fire right up!

To complicate the story, when trying to drive it from the trailer to the shop it wouldn't run for more than a few seconds (like fuel starve) so now I'm going from being certain its something in the wiring to wondering if it's a fuel pump/filter issue! Still have new switches going in it but I'm less confident that'll fix the problem...

Thanks for all the leads, gentlemen.