Line Lock Light

That supplied light is IMO ridiculously large. I went down to radio shack and got me an LED about .25" in diameter. and just stuck it under the tach.
With a manual trans, I also use my LL to be a hill-holder, so I use a toggle to activate it, in that mode; keeping the momentary-on for burnouts. It makes starting off when on a hill so much smoother.

as for endurance, IDK, mine was new in 1971ish, and is now on the third muscle car.. But not in continuous use. I'll guess it has ~30 years on it.