By on May 9, 2009

Captainzerocool writes:

Sajeev, I’ve recently acquired a 1969 Ford F100. It is a solid truck with the 360FE and three on the tree. It does, however, have an electrical problem that I can’t nail down. Apparently, the key or the ignition switch isn’t needed to get the motor to attempt to turn over. Once I attach the positive terminal, the starter motor begins to rotate and will not quit until the battery is disconnected. The starter and starter solenoid have been replaced. Is there some random wire that isn’t/needs to be grounded? Any and all help is appreciated.

Sajeev answers:

For older vehicles in unknown condition, replace your battery cables and clean the mounting surfaces for your chassis/engine ground wires. That’s probably not the source of your problem, but new cables are great fire insurance and keep your cranking/charging system happy. And it’ll cost $20 or less.

But it won’t cure the problem. Probably. So now it’s visual inspection time.

Check for homemade hack jobs. I’d recommend getting a Ford (or Helms) shop manual with a wiring diagram for 1969 Ford trucks. You can spend less for a cheaper manual, but they are harder to use and never as comprehensive. Several on-line places (like eBay) sell reproduction paperback manuals, but you might prefer the cheaper CD-ROM equivalent.

With book (or laptop) at hand, check the wiring harness around the following parts: ignition switch, solenoid, starter, ignition module and starter relay (if equipped).  Look for frayed, rotted or spliced wires near these components. As you probably know, these components are grounded, which somehow connects to the negative battery cable.

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14 Comments on “Piston Slap: You Spin Me Right Round Edition...”

  • avatar
    Dave M.

    How ’bout you?

    RF single-handedly destroyed the domestic auto industry with his uppity “Death Watches”. Or so I hear.

  • avatar
    Gardiner Westbound

    My first suspect would be a defective ignition switch. Disconnect the switch. If the truck doesn’t start when the battery is reconnected that is likely your problem.

  • avatar

    Second suspect: The starter relay (usually mounted on the wheel well) could be stuck closed – whack it with a mallet; maybe it will free up.
    Or, if you have an ohmmeter, check the resistance between the positive battery cable terminal and the starter cable terminal on that relay – it should read high resistance (open circuit). If it reads a low resistance, that’s your problem.

  • avatar

    A guy I knew had a 65 Ford with V8 and granny box. It had an engine fire at a gas station; while they were trying to put it out the truck started moving on its own. It had been parked in first gear and a short circuit caused the starter to turn. Kind of an unnerving thing to happen.

    I concur with GW’s and shaker’s ideas.

  • avatar
    Paul Niedermeyer

    @Sajeev, I wrote you a response to this question when you sent it to me, but it appears to have gotten lost in the ether.

    But the B&B are on it, I see. I have had to replace the ignition switch in my ’66 F-100 twice, but not for this exact reason. But maybe they’re weak. Remove the wire from the ignition switch to the solenoid, and see what happens then. That would verify a bad ignition switch. Either that, or the solenoid, even though new, is defective and stuck open. It can’t be much more than that, since the related wiring is about as complicated as my riding mower.

  • avatar
    Andy D

    Either a stuck solenoid, the wrong solenoid, or boogered wiring around the solenoid. If it was in the ignition switch, the switch would feel funny when the key was turned to start.Generally, the switches dont wear out that way.

  • avatar

    If these don’t work, Congress will give you $4,500 to buy a new Tacoma.

  • avatar

    I had a chance to buy this model Ford truck with the 360 and auto trans from my aunt, who pampered every vehicle she ever owned. All the right service, etc. Heh! Let my wife talk me out of it. Dammit.

  • avatar

    Paul Niedermeyer : @Sajeev, I wrote you a response to this question when you sent it to me, but it appears to have gotten lost in the ether.

    I was wondering what happened! Well, I’ll get you to guest-write this series soon.

    I think the B&B are right, replace the Ignition Switch. But I’ve seen so many hack jobs on this area of old pickups, I wanted to make the visual inspection an important part of “our” answer.

  • avatar

    With the battery disconnected, remove the small wire closest to the battery
    connection on the solenoid.
    Connect the battery, does it try to turn over?
    If yes, replace the solenoid.
    If no, best guess is the ignition switch…


  • avatar

    You can find wiring diagrams for your truck here.

  • avatar


    Frackin’ A! That is what I needed. Thanks!

    @Paul Niedermeyer:

    That is what I am hoping for.

  • avatar


    You have stumbled upon the secret technology that will permit the Chevy Volt to go 40 miles without its gas engine starting. Every Volt will be fitted with an ignition switch from a ’69 F100! Heh.

  • avatar

    Red with a blue stripe is the wire that triggers the solenoid. If it is loaded with 12 volts it will try to start all the time. Shorts can develop in the firewall connector over the years from overheating.

    Are you sure you have the correct solenoid? Some solenoids are pass through designs and have two connectors for signal. If you have one of these, move the red/blue stripe wire to the other terminal .

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