i have a 79 f-250 crew cab 4x4, with a 400 engine and c-6 transmission. when i turn the key to the on or run position, the starter spins, engine spins, and starts, but the starter won't disengage. i turn the key back off not wanting to burn it up. the starter, solenoid, and most of the wiring is new. anyone have any ideas? i have looked at LOTS of similar situations on here, and have not found my particular problem yet. i know its probably something simple, but "it's like a greasy marble. you just can't put your finger on it!" thanks for any help.

 

Sounds like your wires are connected wrong, you are getting constant power to the starter, instead of shutting off when you release the key.

Remember, wire color at the starter wont matter by itself. You have to compare wiring at the switch AND the starter.

Your ignition switch may not be releasing inside, also.

 

I would pull the ignition switch and look at the wiring there. Sound like the start wire is somehow on constant hot lug, or it is frayed with some other frayed wires or the ignition switch is bad.

This is something you can do with a little patience and a text light and volt meter. If the wiring is factory is will likely be in the switch or frayed jacketing somewhere between the switch and the starter, if is it aftermarket it could be in the wrong lug.

If everything looks ok, test the continuity of the lugs on the switch with the positions of the switch using a voltmeter that can read continuity.

Usually this type of thing is either a bad switch, bad wire, or misplaced wiring at the starter solenoid.

 

thanks for the replies. the only "stock" wire left in the switch is the purple and white that goes to the brake light switch, and the red with blue that goes to the nss, ignition control module, and "s" terminal on the solenoid.i have ohmed out the lugs on the switch, which doesn't work out right(according to diagrams that i have seen), but the switch "feels" good. it doesn't drag, or bind, and releases when you go from start to run. i can't figure out how to break the power leg that energizes the starter after it has done it's thing.

 

i have had new solenoids be faulty off the shelf. i have had a brand new one stay stuck on. best thing to do here would be grind on the fender some to make sure you have a very clean ground for your solenoid, and/or add a ground wire to it as well. most problems come from bad grounding. you can test your solenoid by itself by pulling the s and/or i wires. (all of mine only used the one) take a power jumper wire to the first terminal and test that way. i never remember which one is which but i do know the order. your power lug from the battery is closest to the battery. the first terminal to the rear should be the ignition key, then the other terminal which i have never used( i do use it on my mazda conversion to run the white wire of the duraspark2 module) then the starter motor lug. so theres a front-to-rear order you can follow to double-check.
if you do that and doesnt test normal swap out the solenoid. if still abnormal i would look at the starter. this way you can 50/50 your problem test area between the ignition key wiring and starter system wiring.
since the starter is activating in "on" im willing to bet you should swap out your ignition switch and/or check the wiring connector on it. you should not get any power out of the switch in the on position so something is wrong. could be a piece of wire stuck underneath your connector that just so happens to jump across there.

 

The switch has different lugs on the back. There is one that is power in. That is the main lug. It is usually the middle lug - generally marked BAT somehow. That is power in from the battery with the thickest wire. If have a test light or voltmeter and you pull all the wires apart it will be the one that is hot or has power. All the other wires power from this wire.
Once you know what wire and terminal on the switch are hot and BAT all you need to do is take a screwdriver and move the switch with the screwdriver (common tip) to the various positions and see what lugs are constant hot (receive power from the BAT terminal regardless of the position of the switch) and which are hot when the switch is in ACC and RUN and then which lug receives power when the switch is in start. There will be one lug that receives power in start and that lug connects to the wire that is on the solenoid that makes the plunger jump and the starter crank. To find this wire you can use alligators and then connect from the hot wire to each of the other wires individually and see what comes alive when you touch the wires to the power.
Also remember that most of the lugs receive power in run as well as ACC, but some do not. Ignition system should only receive power in run.
Below is the painless harness for these trucks manual.
http://www.painlessperformance.com/Manuals/10118.pdf

You probably do not have one of these harnesses, but the wiring diagrams will help you wring out the wiring, especially the key in the back.

 

thanks for all the replies guys. i am going to try a better ground on the soleniod, and i have tested everything that i can think of. i have read, studied, and looked at GREAT wiring schematics (specific to 79 models), until my vision blurred (just kidding). i am suspicious of the switch at this point as it doesn't have continuity where it should, and does where it shouldn't? i was wondering if i could remove the switch, and "hot wire" a couple of jumpers to lugs that should be hot at all times (such as coil feed, and electric ignition module, and jump to solenoid feed, so i could manually remove that feed, as another way to test the switch).

 

oh, and thanks for the painless wiring diagram, boba fett, it is more in depth (better illustrations) than the universal one that i bought from summit racing (although it is by no means a bad kit. its just "universal"......hindsight????)