How-To: Disable Starter Crank When Engine Is Running.

[lambrkt]

Ever notice that on newer vehicles if you inavertantly turn the ignition key to the start position, nothing happens - i.e. the starter doesn't crank? Nice feature to keep from chewing up ring gear and starter drive eh what? Easy to implement on 80's type Chev/Gmc trucks.

 

Go to your nearest NAPA store and purchase a NORMALLY CLOSED Hobbs pressure switch. Get the one preset to 15psi (but adjustable from 3 to 25 psi). Put a tee and short length of pipe on the oil pressure sending unit attached to the oil filter. Use enough pipe to get the switch away from exhaust heat. Route a wire from the S terminal on the starter to one side of your new switch and route another wire back to the S terminal from the other side of the switch. You are done! You can also tap the sender by the distributor, but it tends to be hard to get to on these trucks.

 

When you crank the engine, you initially have no, or very little oil pressure, so the switch is closed, the starter solenoid gets current and the starter cranks. When the engine starts, oil pressure comes up very quickly and the swich opens cutting off solenoid current so if you inavertantly turn the key, nothing happens. If you have a carburated engine which may have a long crank time to develop oil pressure, turn the pressure setting up on the Hobbs to get around the problem.

 

You can also install a NORMALLY OPEN toggle switch in parallel with the Hobbs to bypass it in case of malfunction (say it sticks open). I have a Painless Peformance bump switch kit on my Burb so I can bypass the starter circuit anyway. If you go this way, be careful, you are also bypassing the neutral intorlock so you can start the vehicle in gear!!