I've just installed an engine start button in my 1970 beetle. I had a really crappy looking cigarette lighter in there so thought I'd replace it with something different.

Got it all plugged in and working, however, the instructions were very vague on how to get the thing illuminated.

I wanted the button to light up with the ignition, then turn off once the engine starts.

Tried to piggyback off the generator light, but when the ignition turns on, the light only flicks on for a millisecond then stays off. Also tried piggybacking off the power for the cigarette lighter, but that didn't work either.

Any ideas on what I should be connecting the button light up to?

You may be able to run it off the oil light, to a relay that makes the start light go on. Normally when your engine is running, the oil light should be off, which would make your starter light be off.

Had a bit more of a fiddle with this engine start button light...

Tried to piggyback off the oil light - no go.

Tried to piggyback off the generator warning light - as before, when the ignition goes on, the light flicks on momentarily. Once the engine starts and the generator light goes out, the light on the engine start button lights up.

I know LEDs are polarity dependent, and if I swap the cables around the light doesn't work at all. I'm assuming there is some mismatch in the current between the generator warning light and the LED in the engine start button.

Anyone with any ideas on how to piggyback an LED light with a normal bulb?

You could use either the gen or oil pressure light but you'll need a relay.

The are both switching grounds which is why you're not getting any love.

The oil light wire would feed the ground side of a relay coil and the ignition supply the positive side for the switch LED back light.

A whole heap of stuffing around for a small bit of bling bling.