my tach has stopped working, so i tested the output on the MSD box. i thought it was supposed to have a steady 5V, but it was all over the place, so i wanted to put my old analog box in just to test.

i have the main set of wires from the box on a connector for easy removal, so simply did the swap. now the car won't start. it sometimes catches, fires, and then immediately dies, kind of like when a ballast resistor goes bad, but of course that is disconnected.

strange thing is when the old analog box is in it act differently. sometimes when i hit the key it almost sounds like a ton of initial advance when the starter struggles to turn the engine over the first few revolutions, and then kicks in. sometimes it fires, only to die immediately.

i have done the test for both boxes, and they do show spark.

i can't imagine what else could have changed, as i said, all the wires out of both boxes are on the same type of connector, so it's just that and then the 2 wires to the distributor, which are on MSD's connectors.

at the moment, i don't know where to go from here. any thoughts?