1970 455 GTO problem
 

Good morning, I noticed my headlights,blinkers and horn were not working on my Saturday run with mt 1970 GTO. Started looking at fuses.Moved a few around and everything all of the sudden worked. This for some strange reason created a new problem. I turn the ignition key, the motor cranks and and begins to start, but as soon as I let the pressure off the key , the engine stops turning as quickly as if I hit a kill switch, Any Ideas ? Any help would be much appreciated !
MSD Ignition - yes

If it were stock, this symptom is caused by the bypass wire to the coil (used in the key's "start" position) working properly but the resistance wire to coil (used in the key's "run" position) not providing voltage to the coil. No telling how your wiring was modified to get both to the MSD ignition.

What happens when you put the fuses back where they came from?

When you say 'blinkers', is that hazard or turn-signals.

Turn-signal power is contolled by the ignition switch.

Hazard, horn, headlights have power at all times. And they all get power from a master splice in the cars hot wires. There's two main splices like this; one under the hood and one under the dash. Wires making poor contact, in one of the splices, could explain the horn and headlight problem.

Need you to do a key-on/engine-off and see if turn signals work. Got to try and figure out if turn signal loss was caused by a fuse or power loss from the ignition switch.

If blinkers meant turn signals it sounds like you have or had two different problems.

Wires to the ignition switch would have been right above your hand when you reached into the fuse box. May have wiggled something there that's now causing the cranks over but no run deal.

Got a few possibles on this one

Clay