So I have a 78 F150 that turns over and fires. It acts like it wants to start but won't stay running. I have replaced the ignition modual with an msd 6a box and hooked it up. ( to what I think is correct). I have rebuilt the carb and replaced the fuel pump so I know there is gas getting in there. I can see the jets pushing the gas in. I don't know where to go from here.
I had a problem getting power to the ignition switch but found a wire not connected properly. Now I have power to that.
It's halfway timed with my new distributor. I know it's close. But waiting to get it running to dial it in.
Just can't keep it on. Looking for suggestions. Thanks

 

Welcome to FTE.

I assume it started fine and ran before installing the MSD? Double-check all your wiring and connections. I am talking about being methodical - wire by wire.

 

Check for power at the coil with the key in RUN

Josh

 

Thanks for the welcome. Yeah before( about 4 years ago when I drove it). It worked fine. At the time I changed the intake , carb, distributor, box and coil. I've recently started working on it again. I put an edelbrock air gap intake, an edelbrock 4 barrel 1405 600 cfm carb, an msd ford ready to run distributor, 6a msd box and a blaster 2 msd coil.
I think the problem is in the wiring soewhere.
I do not have power to the coil with the ignition in run. But when I turn it over it does gets power to the coil.

 

There's your problem.

The coil receives power from the solenoid during crank. Specifically the "I" terminal.

After the key is released the power is then transferred directly from the ignition switch via the pink resistor wire.

Either something was cut or the resistor wire burned up.

If you are running an aftermarket coil and ignition, some of those require straight 12V power and not the OEM resistor fed less than ~9 volts.

If that's the case you can make your own key-on power wire.

Josh

 

So here is what I did.


I followed these instructions till I got to the 12v source.


This is the wire I used (which I thought was the 12v that led to the ignition. But I don't think it's working properly. This wire came from the connection to the old ignition module. It's blue and red.




Here are the wiring diagrams from my book. You'll see the blue and red wire that leads to the starter relay and through the neutral safety switch to the ignition.

Where do I go from here?
and
How can I make my own 12v key on power source?

 

Should I use a Bosch relay from the 12v source I was using? Would that fix the issue? Or would I need to find a diff source without a relay? Or with a relay?

 

1974/79 FoMoCo vehicles with DuraSpark: There are two possible resistor wires:

D1AZ-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-84-A).

60" long / Color coded red with green stripes / 1.30-1.40 ohms resistance / #16 gauge wire.
-----------------------------------------------------------------------------------------
D7AZ-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-213).

49" long / Color coded red / 1.30-1.40 ohms resistance / #16 gauge wire.

 

Here is what I did with my 6AL box if it helps you at all. I find it interesting that there have been a couple threads pop up recently with the same/similar issues with MSD boxes.

https://www.ford-trucks.com/forums/1...l#post11885763

 

Thank you everyone. With all the advice and a little realization i figured it out. Truck is running. My next thread will be with a timing issue. Thanks guys I appreciate it.

 

jut a little FYI i was using the wrong 12v source. had to find the correct wire. For some reason i didnt think to check the voltage on the wire i was using