When cranking the car over with the ignition system disabled, such as for a compression check....I've always disconnected the wire from the coil to the cap and put a thick rubber cap over the coil terminal. I've just thought about this now...at like 50,000 volts...could this be damaging the coil by causing some sort of feedback or something? Is it better to, say, leave the wire on the coil, but pull it off of the cap and ground it somewhere away from the engine? Thanks.

 

What you're doing is fine. There is no path for the current to follow, so there is not voltage going through the coil.

If you were to ground it, you would get voltage running through the coil, as well as through the whole engine. Not really bad, but you'd have to be careful about letting a wrench ground out.

 

Oh alright..I gotcha.. So the coil doesn't fire unless it's got a completed electrical circuit?

 

Right.

 

It makes more sense to disconnect the primary (12V) side of the coil and leave the secondary (high voltage) side alone.... then there's absolutely no possibility of spark

 

It makes the most sense to get in the habbit of disconnecting the negative battery post every time you're working with something electrical, or for any part of the car for that matter.

 

but that sure makes it hard to crank the car over, eh