Recently I was baffled by my distributor and coil system was not producing a spark at the plug even though I was getting power to coil and distributor.  Out of the car and on a test fixture spark was produced.  I tested a few distributors and coils all the same results.  My wiring harness is a reproduction appearing in good condition.i hooked up a headlight bulb to a load on to see if it would light, it didn’t.
 I made some ten foot jumper cables going from the ignition switch to the coil, it lite the head lite bulb



. Got spark and determined something amiss in the wire from the ignition switch to coil so I replaced it an all is good.
Point being even though the original wire produced twelve volts apparently there was not enough amps to push it.
Attached is my test fixture