Check Engine or Service Engine Soon lights have the common attribute that they stay on long enough in "start" that if you're looking for them you'll see them, but if you're not, they're unobtrusively quick-on, quick-off. How are these lights wired to get this on-off feature and then be turned on for longer periods when the car's computer wants to annoy the driver? I suspect there are relays involved...or...heaven forbid its all controlled by the black box.

I'd like to custom wire such an indicator light that will test, for example, the headlight circuit to show if the circuit is being completed when I turn my headlights on.

Thanks.

If I am not too mistaken, when all dash board lights lits up when having key in START position, it is a dash lamp test and not a curcuit test.

Most cars today have a "lamp out" indicator in dash that comes on if load is too low in curcuit. A unit like that can be grabbed from almost any Ford vehicle on the yard and is normally located above glove compartment.

herman, thanks for the response! I like your idea about the Fords...the little research I've done suggested some very elaborate solutions to an easy task...for example, I heard that one solution was to mount a light sensitive sensor in front of the headlight and if the headlight doesn't give off enough light, then the warning light comes on. Yikes!

Anyway, about those Fords...could you name one or two models or years that would be sure to have the "lamp out" indicators above the glove box: like 'any lincoln in the 80's'...'or the 77 Fairlanes', etc. There are so many Fords to choose from. Thanks again. Dave