how do you tell if a distributor is good or not?

take your plug wires off the spark plugs not the cap then take a spark plug put it in the wire then have someone turn the key make shur that you set the plug on the motor so it can spark also it could be your cap and roder

Alternatively, take the spark wire off the plug and hold the bare metal about 1 to 2mm from a bare earthed spot on the engine or the chassis (make sure not to touch) - saves you from having to take the spark plug out, but if you want to play it safe it'd be better taking it out.

how do you tell if a distributor is good or not?

 

the short answer is that a distributor can test fine but still cause the car not to start. there is no definitive way to test a distributor, usually you can, but there are times when you can't (i've had it happen twice). long answer follows:

i've had a distributor generate spark but not work properly. less than a month ago there was a thread about this and we went through all this before so if you're interested in that discussion do a search. mostly about the problem i'm about to talk about being "impossible". but to be quick i've had two distributors fail in different subaru's that would generate spark, even pass the FSM tests but still the car didnt' start. couldn't resolve the problem until i finally swapped the distributors and it started. both times it didn't fail while i was driving, i had taken the car off the road for a couple weeks/months for repair or swaps and the previously fine running vehicle and distributor failed to start the car. my guess is the crank angle sensor gets corroded or out of alignment somehow. that being said, there was no proper (practical) way to diagnose mine. i'm sure with some crazy computer/oscilloscope set up it would have shown up, but who's going to go through all that?