Brake Pedal Cranks Engine
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New User
Joined: Nov 2005
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Brake Pedal Cranks Engine
I have an 87 F150, 4X4, 351, auto.
Recently, when the truck is in Park or Neutral, I can press the brake pedal and the engine will begin to crank. This will happen regardless of the key being in the ignition. If the key is in the run position, the truck will actually start and run.
The only wires coming from the brake pedal are from the brake switch. Does anyone have an ideal as to why this would be happening?
Thanks for the help in advance.
Recently, when the truck is in Park or Neutral, I can press the brake pedal and the engine will begin to crank. This will happen regardless of the key being in the ignition. If the key is in the run position, the truck will actually start and run.
The only wires coming from the brake pedal are from the brake switch. Does anyone have an ideal as to why this would be happening?
Thanks for the help in advance.
Post Fiend
Joined: Jan 2005
Posts: 8,402
Likes: 10
I am no electrical expert but two things spring to mind.
The output from the brake light switch at the pedal runs up the steering column first, the ign switch is on top of the steering column under the dash so maybe the wire from the brake light switch is bare and touching the wire to the starter relay coming out of the ign switch.
Next, after coming back down the column the brake light power runs in the harness along the frame rail to the rear lights. The wires to the neutral safety switch on the drivers side of the transmission may damaged and getting power from the braKe light wire in the harness on the frame rail.
You will need to examine the wiring and look for any damaged insulation.
The output from the brake light switch at the pedal runs up the steering column first, the ign switch is on top of the steering column under the dash so maybe the wire from the brake light switch is bare and touching the wire to the starter relay coming out of the ign switch.
Next, after coming back down the column the brake light power runs in the harness along the frame rail to the rear lights. The wires to the neutral safety switch on the drivers side of the transmission may damaged and getting power from the braKe light wire in the harness on the frame rail.
You will need to examine the wiring and look for any damaged insulation.
Lead Driver
Joined: Aug 2006
Posts: 5,670
Likes: 13
From: Sand Lake, MI
Mine did the same thing, the harness connector directly under the master cylinder and steering column.
The casing on the wires leading into and away from it corroded away just enough to expose the bare wire.
That allowed cross connections between circuits.
I cut out the connector eliminating it, soldering in short sections of wire with heat shrink tubing to protect/insulate the connections.
The casing on the wires leading into and away from it corroded away just enough to expose the bare wire.
That allowed cross connections between circuits.
I cut out the connector eliminating it, soldering in short sections of wire with heat shrink tubing to protect/insulate the connections.
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New User
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I checked the connectors under the brake booster and all of the wires leading to the connectors were stripped back by 1-3 inches. I removed each wire from the connectors one at a time and taped the exposed wires. This seems to have fixed the issue.
Thanks again for the help.
Thanks again for the help.
Senior User
Joined: Apr 2002
Posts: 122
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From: Lewiston, Idaho
What a perfect example of why forums like these are great! Such a vast array of collective knowledge here. When I first read this it seemed like such a wildly isolated problem, but no, happened before, check this etc. OP gets back to confirm that's what it was.
GREAT job guys!
GREAT job guys!
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Another update...
Before I was able to get the wiring taped, the starter engaged and burned itself and the solenoid out. I guess the right wires at the connectors touched and began cranking the engine...while I was driving at around 35mph. Before I could get pulled over, it quit cranking and ran normal. It wasn't until after I taped the wiring and tried to start the engine that I found out something was not right. The solenoid would click, but no voltage was getting the the starter. Replaced the solenoid, verified voltage at starter, but the starter was locked up. Took the starter to the parts store, verified it was toast, got a reman unit, bolted it on, and the truck fired right up.
Now...on to the next project.
Before I was able to get the wiring taped, the starter engaged and burned itself and the solenoid out. I guess the right wires at the connectors touched and began cranking the engine...while I was driving at around 35mph. Before I could get pulled over, it quit cranking and ran normal. It wasn't until after I taped the wiring and tried to start the engine that I found out something was not right. The solenoid would click, but no voltage was getting the the starter. Replaced the solenoid, verified voltage at starter, but the starter was locked up. Took the starter to the parts store, verified it was toast, got a reman unit, bolted it on, and the truck fired right up.
Now...on to the next project.
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