My truck starts just fine but as soon as I release the key to the run position it quits. I'm guessing that the ignition run circuit has a break somewhere but I have no idea which wire I should check. Does anyone have a wiring diagram that shows which wire would be suspect? I have looked at several diagrams on the internet but I have no idea which wire I should be checking. It's a 78 F150 Custom with a 302 4 speed trans.

Thanks in advance for the help..

Bob G

 

It's either the ignition switch itself or the resistor wire that's at fault.

Check the three wire plug about midway on the firewall, it will have a white wire w/red stripe, red wire w/white stripe and a red wire w/green stripe.

With the ignition switch in the "RUN" position check for voltage at the red wire w/green stripe.

 

The resistor wire under the dash was my problem once, just cut it out and splice in a new one.

I agree a bad ignition switch can do that too.

 

Here is a simple diagram that has been posted before on the DuraSpark. It should help you understand what is going on.

 

Thanks, it looks like the weather this afternoon will be good enough to dive into this and find the problem once and for all.

"The resistor wire under the dash was my problem once, just cut it out and splice in a new one." Jim, is this going to be the red wire with the green stripe or is it some other color?

Again thanks for the info.

Bob G

 

Well, I got it running this afternoon even with the rotten weather. The parts came in the mail this morning and the first thing I did after lunch was to change out the switch and viola it started and stayed running with the switch in the run position.

Now to pull the carb and to through it, the accelerator pump is leaking, and the old girl should be back in running condition once again.

Thanks again for your help....

Bob G