I’m having an electrical issue and would like some feedback. First a little background on what I’m working on in the hopes of getting direction from members here…

I’m working on an 81 D150 and found the Gear Vendors overdrive wouldn’t up or downshift. This is after proving the solenoid that shifts the overdrive was working correctly. This is also on a mechanically fresh overdrive unit. A gear vendors rep told me to by-pass the gear vendors electronic controller by wiring in a separate switch to the solenoid on the overdrive unit. This was a means to isolate where the problem may be. Simple enough.

The gear vendors solenoid has 2 terminals which have no-polarity. I ran a ground wire direct from the battery to one of the 2 solenoid terminals. Next, I wired-in a single pole, single throw LED switch using a fuse tap in a fuse location that is “on” when the truck is running (in this case the radio). This was the means to provide power to the switch. Then I ran a simple ground wire from the switch to the firewall. The final lead from the switch was the “On or LED” position out to the other solenoid terminal. This would only be energized when the switch rocker was moved to the LED or “On” position. The solenoid requires a 3 amp circuit which is the same as the radio.

When I went to start the truck, the fuel pump came on but the engine would not turn over. I checked fuses under the dash and all were OK. All of the wire connections were good. I thought I might have caused another lead to disconnect when pulling the (very) few wires needed to hook up the switch. All looked OK. Certainly, nothing else I did would seem to have caused an issue with this simple wiring job.

However, when I went to start the truck, I could hear the electric fuel pump running but the engine would not turn over. I re-traced the route of the wires I pulled and found nothing unplugged, shorted, etc. I did find a 30 amp fuse that was blown but I don’t know if that was blown before or after my work. This fuse is under hood and is one of 5 or 6 that were apparently added to replace the factory fusible links. I have to assume the fuse blew after I tried to start it since the truck started, ran and drove before I wired-in the switch. I replaced the fuse and disconnected all of the overdrive by-pass connections I made. The result is the same, the starter does not turn the engine over.

I'm at a loss as to what happened and why. Thoughts / Suggestions are appreciated.

Well, it'll be hard to sort out remotely. It's not stock, there is no electric pump in a stock 81, plus the fusible link issue plus who knows what else.

the starter only needs two connections, well three but the third is via being bolted to the engine. You have one fat cable from the battery + and a smaller wire from the starter relay. The small wire from the relay is what tells the starter to turn over. For that relay to work you need 12v from the ignition switch AND a ground thru the neutral safety switch. Did you happen to knock off there connector at the NSS? Put a meter on the starter relay and see if you are getting the ground and check the 12v in start as well, need a helper as well.

Yes, Understood. This is made a lot more difficult in that it's not my truck and I didn't make any of the mods but all of that aside, I ran only one "positive" lead (from the fuse box) so I assume that has to be what caused the fuse to blow (unless it was blown before). Where is the NSS located from the factory?

Assuming an automatic transmission, it's on driver's side right below the shifter linkage hook up. See the hole in the pic? That's where it goes. Should have three pins on the switch with a three wire connector having a rubber boot.

[img]http://www.forabodiesonly.com/mopar/attachments/727-kickdown-and-shifter-2-jpg.155560/[/img]

If it is a stick trans, then you have to push the clutch in to start it.

Yep. This is a 904 Torqueflight. I'll check this tomorrow when I get back to the storage unit where the truck is kept. Thanks for your help.

You could also try holding the brakes on and shifting from park to neutral while holding the key in the start position. If it tries to start then you will know it's a shift linkage adjustment that you need.

Good Point. This made me also wonder if the transmission wasn't fully in Park or was barely in and then slipped out after I shut the truck off (before I started the by-pass job).

Yep. It ended up being that I had completely knocked off the connector for the neutral safety switch. Being black with a light coating of dirt and grease on the cap and the leads, I just looked right past it. I re-connected that and the truck started right up. I noticed too that the overdrive control was lit the way that it's supposed to be so Monday I'll have time to drive it to see if the controller is working now too (due to replacing the blown fuse).

Thanks for pointing me in the right direction.

Glad it was something simple.

it's always a good feeling when something simple is the guilty culprit !
glad you got it fixed.