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Alright yall my 76 F250 Highboy has some ignition problems and I have no idea where to start. It has the 390 V8 and MSD Ignition. The problem is that sometimes it will crank and run right away and other times it will crank until the battery is dead but it won’t run. I’ve noticed that when I turn the ignition to the run position and the dash board lights up and has the seatbelt light on, then it will run. It runs for about 5 minutes then it will just shut off for no reason. When I turn the ignition to the on position, and the dashboard doesn’t light up is when it will crank all day but it won’t run. Please help, this one has me beyond confused because I’ve never seen this before.
Check for power at your MSD box with key on when it won't start. May be losing power from ignition switch as mentioned above or a loose wire somewhere feeding your Msd box. Could be a MSD box is failing intermittenly.
As mentioned above, it sounds like you are losing the primary side of the ignition somewhere. There are many possibilities. I have had an MSD box fail for me as well as a Duraspark control module. Both stopped the secondary ignition voltage. As advised, you will have to trace out the circuits when it is not working. It can be tedious, but it will be needed to find the problem. The good part is that you are working on it at home instead of out on the road somewhere. Two of my failures happened on the side of an Interstate highway with 80 MPH traffic a few feet away. That can produce stress!
