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1979 302 4 speed on the floor. Ran fine then stalled.
It will start every time... Until I let go of the key.
Once I let the spring of the key go back, the engine shuts down. If I hold It in the start position (with the spring engaged) it will continue to run. What should I check? Thanks
Yep, and if it's not that, the ignition switch: it's running while cranking because the coil gets +12V from the "I" terminal on the starter solenoid, bypassing the resistor wire. With the ignition switch in the run position, the coil gets ~9V from the switch through a resistor wire. If you have voltage at the ignition switch in the run position, but not at the coil, the resistor wire has failed. If you don't have it at the switch either, there's your culprit.
I just came back from tracing the resistor wire. I tried to start it again and it started as it should. I know the problem is not solved, but it leads me to maybe believe it is the wire?
I don't know. Thanks for the help. I will need to do some searching.
Yeah, most likely either a break in the wire that's making contact again now that you moved it, or a bad connection somewhere along the way. Once you've got it running, you can try wiggling the wire in various places to see when it dies, in order to locate the problem.
My '77 F-100 did just what you are describing, including the disappearing problem game, for over 6 months while I was trying to figure out the problem. It finally wouldn't run at all with the key in the run position no matter what.
I replaced the switch and haven't had the problem since. We may not have had the same problem, but I figured I would let you know what finally fixed mine.
-Scott H.
Oh, just a FYI... Police officers start getting REAL inquisitive if you're testing out the system with the new key switch hanging by the wires and the original one is still mounted in the dash.
I may need to get a new switch and test it out. The problem is back now and it wont stay running again. I also may take all the tape off the wires tomorrow and trace that resistor wire.
Is there a jumper or way to hot wire the switch to determine if it is or is not the switch?
I wont do this in public in fear of getting questioned.
I would think you could run a toggle switch with one lead tapped into the 12 volt wire at the switch and the other tapped into the run wire, but I don't have a diagram right now to tell you which one is which.
Oh, just a FYI... Police officers start getting REAL inquisitive if you're testing out the system with the new key switch hanging by the wires and the original one is still mounted in the dash.
duno if I quoted that right, but I would love to hear that story
I had this very same issue recently. After a lot of testing and playing with the ignition....it indeed was the ignition switch, and ignition lock cylinder. Solved all problems. Very easy fix as well. Hope you solve the problem!
With the ignition switch in the run position, the coil gets ~9V from the switch through a resistor wire. If you have voltage at the ignition switch in the run position, but not at the coil, the resistor wire has failed. If you don't have it at the switch either, there's your culprit.
I have ordered a new ignition switch which I should get in a couple of days. In the mean time, I was looking at this advice. I have not checked the voltage yet, but I was able to disconnect the ignition switch from the harness and try to hot wire the truck. It will start, but It still wont continue running if I let the key go. That means I have voltage at the switch right? And it eliminates the bad switch question?
So should my next test be to check for voltage at the coil and see if I have 9v?
I received the new switch today and installed it. Same problem. I took apart the dash and found a hot wire (in temperature).
The red wire coming out of the switch is hot. I started to follow it toward the passenger side where it picked up some insulation.
The wire looped back toward the driver side at about midpoint in the cab.
The red wire came to a tee where three wires met. In this picture, the red hot wire is the one facing down. The two color wire on the top goes through the firewall to under the hood on the driver side. The brown wire to the right goes back toward the passenger side and exits to under the hood
It this a fuseable link gone bad?
What is this? I am going to look at a wire diagram now.
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