When I take my foot off of the foot starter the engine dies, and the starter continues to spin a bit.
If wired correctly there should be a resistor bypass wire running from the small terminal on the starter switch to the positive terminal on the coil.
If the truck runs in the start position but dies when you let up, it is not getting power from the ignition switch, just the bypass.
This does not explain the starter run on problem, only the dying problem.
