1978 f250 400/c6

Hello all,

I need to find what wire energizes the coil while cranking. I had an old chevy before that put juice to the coil while cranking on one circuit and then a different circuit while running.

When starting my truck, it feels like it will not fire while in the start position and once i let the key back to run the thing will start. Like no spark while cranking. Before i climb up into the thing, can someone guide me where to start looking.

Thanks,
Chris

 

Before you go ripping out wires and/or cursing the PO, have you not a service manual? A Haynes or Chiltons as well as a factory service manual will do. There's all the electrical diagrams you need.

Anyway, on your starter solenoid, the RED/b wire goes to the 'S' terminal and closes the contacts such that the starter is engaged. Since the starter runs this wire is fine. The 'I' terminal has a BROWN wire and its job is to provide BATT voltage in START to the coil...once started, its job is done and no VDC should be realized there. The ballast resistor circuit takes over and ~ 8VDC is supplied to the coil......Not unlike your old Chubby, as well as a plethora of other vehicles.

You don't have a wiring problem here...there's something gone south with the primary starting circuit or there's some dirty connections in the same area.

Question: When you let off the key to RUN, does she stay running or poop out?

 

In a perfect world, the Red w/green wire from the ignition switch to the coil and ignition control module should actually have power in both RUN and START. Along with the Brown wire mentioned to make sure that the system gets the full battery voltage when cranking, things usually work as expected.

Since yours is only firing up when you let off the key, it sounds like you might have more than one issue at a time to deal with.
One would be a failing ignition switch (no power to the ignition in START) that is only sending power up the line in RUN.
The next would be a failing starter relay/solenoid that no longer sends power out through the Brown wire.

I'm not sure if anything going wrong with the ignition control module (ICM/Duraspark box) could mimic those symptoms, but they do go bad and if there is something there that could be causing it, it would be hard to see and test for without simply replacing the module.
I hate throwing parts at a problem (but have done it many times anyway!) but I'm not sure how to test a module other than to put it on another vehicle with the same connectors to see if it works there.

A failing radio noise suppressor/capacitor/condenser/thingy can cause a no-start issue when it short circuits to ground through it's case, but that will keep it from running at all. Not just in START.

Good luck. Probably more things than I can think of at the moment, so maybe someone will chime in with the cure.

Paul

 

1Ton: There's only a couple of things that are messed up that match the OP's description. There are voltage tests to determine if the ICM is pooched but I don't think it's that.

Before giving a "possible" component failure scenario, I like to have questions answered...and then on to troubleshoot one symptom at a time. I'm simple like that. And the OP hasn't answered one question. Mebbe he figured it out already.

Before fixing a broke whatchamuhcallit one has to know how or what caused it to break. Otherwise, one is reduced to throwing parts at the booger-man in hopes something scares him away.

 

Thanks guys,

Thanks for confirming there is two circuits to the coil. I will do a little testing and it should not be a problem to hunt down.

Chris

 

So you're looking to fix the "Not fire while in the start position and once i let the key back to run the thing will start" issue? Or is there something else?
If so, please answer the question I posted earlier (post #2) as there are some simple troubleshooting tests to determine to root cause of this illness........that is, of course, if you want our help. If you have other ideas and want to go it alone, well, good luck.

 

It stays running. The truck starts every time, Just i notice the lag/delay sometimes and it reminds me of my `55. After I get my headache of a suburban out of the shop i will bring in the ford and do some testing on the information posted. It may be something simple like a bad connection.

I will post what i find in a few days,

Thanks for all of the info,
Chris