Ignition firing when it wants

[jonkmbll89]

I have an 85 short bed with a 350. My problem is it only fires up when it wants to. I am getting power to the distributor. I have changed everything out inside the distributor. Today I traced the problem to the box under the dash. I would try to start the motor and when it wouldn't start I would tap on the box and the motor would fire up. I would like to know what the name of the box under the dash

[Lt.Del]

You have an 85, so that rules out a computer.  Do you have a digital camera you can put up a pic.  Where is the box under the dash? by the steering column, heater, under glove box?
My guess would be that your problem is the ignition coil.  Do you get spark at the plugs when it doesn't start?

[Fordeatinz71]

that "box under the dash" makes me think it's an old alarm system with an ignition interruptor.  it was probably "disabled" but not removed, and now it's malfunctioning and cutting ignition power...

[Captkaos]

It is the ESC (Electronic Spark Control)  Bypass it and you will be much better off:
http://73-87.com/7387garage/drivetrain/escrepl.htm

[jonkmbll89]

Bypassing the ESC worked. Thanks Captkaos.

[Captkaos]

No problem.  That is a common issue.  When those things go bad it is a major pain.