won't stay running without ignition switch to "start"

[farmtruckman]

My 72 F100 with 400 ci, won't stay running unless ignition switch stays in "start" position. Already changed ignition switch and starter solonoid. Some one mentioned "ballast" and can't locate anything. Where would 'ballast" be? Wiring on this truck is a mess so any photos on what I am looking for would be greatly appreciated. Not much else can be wrong. Truck fires right up, otherwise.

Thanks for help in advance.

FTM

[fordman]

the original resistor wire is a pink wire behind the ignition switch plug. but all the evidence still points me to a bad switch. or a loose connection to the switch.

[cdeal28078]

I remember a little something about if the 2 smaller wire in the middle of the starter solinoid are switched it will act like this. Might want to check them out
clint

[knightfire83]

fordman is correct. The coil is not getting any power from the ignition switch. Instead it is getting it from the starter solenoid ( I terminal, brown wire) when it is cranking over. The solenoid sends 12volts directly to the coil to start up, but then the ignition switch sends a lower current to the coil to keep the points from frying when running.

Somewhere between the ignition switch and the coil the circuit is broken. As indicated, it is a pink resistance wire from the back of the switch that leads into the engine compartment.

http://www.fordification.com/tech/wirin ... _quick.jpg

[RustyBolts]

fordman is correct. The coil is not getting any power from the ignition switch. Instead it is getting it from the starter solenoid ( I terminal, brown wire) when it is cranking over. The solenoid sends 12volts directly to the coil to start up, but then the ignition switch sends a lower current to the coil to keep the points from frying when running.

Somewhere between the ignition switch and the coil the circuit is broken. As indicated, it is a pink resistance wire from the back of the switch that leads into the engine compartment.

http://www.fordification.com/tech/wirin ... _quick.jpg

Dad and I had this same problem whip us on our 1961 John Deere 4010 Gas. Replaced the Resistor Wire, and then it ran like your grandma's Singer sewing machine. The only difference here is that the solenoid is on the starter, and not remote mounted like it is on a ford pickup.

[1971ford]

You have to have it on "start"... wouldn't that mean that you are continuosly grinding the starter gear with the flexplate?

[RustyBolts]

You have to have it on "start"... wouldn't that mean that you are continuosly grinding the starter gear with the flexplate?

To keep it running, yes i'd imagine. at least that's how it was on the 4010. It'd fire, but once you let off the key, it'd die. I think that's what's he's experiencing here.

[1971ford]

Ahh.
I had this same problem a few days ago, well the truck would not start at all, when you turn the key on it would fire once or twice unless you held it. If you held it, (i wouldn't hold it for long, to prevent a lot of grinding) it would keep firing, but would stop once you let off the key.
I fixed it yesterday by wiring the choke up.