Electrical Problem in Starter System of my 1976 Ford F-100?

Question

Please reference the second diagram called 'Automobile Starter Circuit' at: http://www.misterfixit.com/electrical_circuit.htm

Fact 1: If I bypass the Starter Solenoid and go directly from the battery to the starter, I can start the truck.

Fact 2: I installed a new Starter Solenoid and I get the same results (truck doesn't start) with the old and new solenoid.

Fact 3: I bypassed the Ignition Key Switch by putting a wire directly from the post on the solenoid that gets power from the battery to the post on the solenoid that completes the circuit from the Ignition Key Switch without success.

Fact 4: I bypassed the Transmission Neutral Switch by grounding the wire directly to the frame of the truck expecting the truck to start in any gear, but this didn't work.

Question: Since I can start the truck by bypassing the solenoid, I thought only 3 things could be bad (the solenoid itself, the neutral switch, or the ignition switch), however, none of these seem to be the problem. Any ideas?

Answer 1

If you can start the engine by shorting the two big terminals on the solenoid together, but putting 12v to the little terminal that goes to the ignition switch doesn't work, only two things can be wrong. The solenoid is bad, or you don't have a good ground to the other small solenoid terminal that goes to the interlock.
One way the ground might be bad is if you don't have a good ground connection between the engine and frame. The battery grounds to the engine but the solenoid and everything else grounds to the frame, so if you don't have a good connection between the two, nothing will work.
Try doing fact four by hooking the ground wire from the solenoid to the battery neg. instead of the frame.

Answer 2

1976 Ford F 100

Answer 3

You sir have a grounding problem with your starter solenoid.
Take the bolts back out, sand the fendewell and try again.

Oh, how's the ground strap from the engine to the frame?