The NSS is a safety mechanism preventing the engine from starting unless the transmission is in park or neutral. When you jump the solenoid, you're bypassing this switch entirely, allowing the engine to crank regardless of the gear selection. Since it starts in drive, the NSS is definitely malfunctioning and failing to interrupt the starting circuit when the gear selector is in drive.
Here's why this happens:
* Faulty NSS: The switch itself might be worn out, broken internally, or have a poor connection. The internal contacts may be stuck closed or intermittently failing.
* Wiring Issues: A short circuit or break in the wiring leading to or from the NSS can also mimic a faulty switch. A wire might be touching ground or another wire incorrectly.
* Transmission linkage problems: Though less likely, problems with the linkage connecting the gear selector to the transmission could lead to incorrect signals being sent to the NSS. The transmission might *think* it's in neutral even when it's in drive.
In short: Jumping the solenoid proves the starting system itself works, but the safety mechanism (NSS) is completely failing to perform its function. Replacing the NSS is the most likely solution, but thoroughly checking the wiring is also recommended to rule out other electrical issues. Attempting to drive the truck while this problem exists is extremely dangerous.
