i have a 56 ford f100 with manual tranny. my truck will only run if the key is held in the start position. once i let go of the key the truck dies. I have replaced the ignition siwtch and ignition cylinder. Any ideas?/

 

Check and see if you have a ceramic resister to reduce voltage. If your ignition has one and is wired correctly the voltage bypasses it when the ignition is turned to start and goes back through the resister when the key is release. If that resister goes bad it will run in start but not in the run position. You can double check by temp. running a jumper wire across the two resister post and it should run.
Hope that's your issue, if so replacing the resister is a cheap easy fix.
Larry

 

I think you may be missing the wire from "I" on the start relay to the resistor prior to the ignition coil. As a test you could jumper a wire from the + side of the battery to the resistor prior to the ignition coil. This is with the ign switch to start then release to on/run/normal position. Don't leave the test wire on to long. You may have broken the original wire on either end by accident. chuck

What Larry said also.

 

thanks those sound like issues i was thinking also. where would the ceramic resistor be located, im not too familiar with that. ??

 

The stock location for the ballast resistor is the firewall, if you follow the wires from the coil you'll find it. One side of the coil has only one wire...it goes to the distributor. The other terminal of the coil should have two wires...one to the starter solenoid and the other to the ballast resistor. Here is a photo of a ballast resistor for reference. It is about 3 inches long and about 1 inch on a side.

 

well thank u very much charlieled for the pic and wiring explanation. I fixed it and it now runs without holding the key!!. thanks all for the info