I own the above truck (300 CID straight six) and recently detailed the engine compartment as well as cleaned up the wiring. Before this all was working fine. Regarding the wiring, I took extra care labeling all wires and connections so that when they were rerouted, lengths of damaged wire replaced etc. that the circuits would remain as they were. When it came time to start it up, I turned the ignition switch to run (dash lights on, accessories work) and then held the switch momentarily to start. The starter cranked and kept cranking even after I released the key back to the run position, turned it to off and still cranking. I had to disconnect the battery from the solenoid. Upon attempting to reconnect battery to solenoid, shorting occurred. Something was grounding. I removed the battery's pos. lead and bypassed the solenoid and starter and applied it to all other power circuits and all seemed fine. Tried to connect the battery + directly to the starter and zapp, shorting (multimeter shows no resistance between starter lead and ground, direct short). Upon removing the starter I found a lot of corrosion. This did not answer my "runaway starter" scenario but I ordered a new starter anyway since this one had shorted.
Before connecting the new starter I checked that the solenoid was functioning correctly. I connected the battery + to the incoming voltage stud, left the starter off the switched post and applied current to the "S" post by turning the ignition. The solenoid clicked and disengaged upon turning the ignition switch back to run, then off (I did get 12V at the starter post).
Next I left all power feeding terminals (i.e. volt. reg., ign. ect.) off the incoming stud except the battery and the alternator wire. I did this just to isolate the ignition system and just see if the starting circuit with the new starter worked properly. I connected the starter to its stud and removed the "S" stud wire from the solenoid and applied 12V with a jumper to the battery. The new starter turned fine, removed the jumper to stop. Then I hooked up the starter wire back to the solenoid. I connected all my power feeding terminals (i.e. volt. reg., ign. ect.) back to the batt. side solenoid stud and tried for the first time since my last attempt to start the engine. I turned the ignition and the engine turned. I did this only for about 3 seconds and then to off and run just to see if the solenoid would disengage the starter, it did. Then I cranked it over for 10 seconds. After no start I turned the key to run then off. The starter DID NOT disengage and I had to remove the battery terminal to stop. Upon attempting to reconnect the starter it shorted. I repeated the same thing that happened the first time and burned out another starter! I thought the old starter was perhaps the cause of the problem however the problem still exists somewhere. Meter check confirms direct short to ground on the starter's post.
My question, why did the starter at first crank - then not stop - then short on second attempt to apply power. I can imagine how I am shorting the starter since it does not have an onboard solenoid. Could I be somehow overloading it? And why does it work until I manually disconnect it then short and not work upon reconnecting it? In other words, what is causing it to initially operate while shorted? It seems I messed up somewhere with my wiring, regardless of how careful I was.
NOTE: This '69 model at some point had its original 240 CID point driven engine replaced with a post '74 300 CID with electronic ignition complete with module and all. Apparently done correctly since the engine ran fine.
Thanks for any help you can provide as well as for holding out through the long explaination!
I believe that truck has a fender mounted solenoid. With battery to one side of solenoid then on the other post there is a wire going from the solenoid to the starter. then a single smaller wire that comes from the key switch. take the small wire off and check with a volt meter should be close to battery voltage on this wire with the key in the start position and no voltage in the run position. If it has voltage in the run position its wired wrong. If it works like it should replace the solenoid it is more than likely sticking.