Previous owner Neutral safety switch bypass

[Scottcoda]

Hey guys, I have been getting my new to me 68 2500 road worthy and my last tackle is the back up lights, Changed the bulbs, fuses, cleaned the light terminals and still no back up lights, so I thought I would start at the cab to see whats getting power and see if I can track down the problem, Well I found the problem right off the bat, The Neutral safety switched was bypassed by previous owner, the switch is still there just nothing connected to it and I can't seem to find anything that should connect to it. I would like to get the switch back in service, I know I can get a new switch(thinking the po prob bypassed cuz it is broken) and a new pigtail to plug into it but where do the wires go from there? Pretty much any info to get the switch back in service would be great.. All input welcome thanks guys!! Scott (68 gmc 2500 4.1 w/ auto 400 tranny)

[WIDESIDE72]

I take it you have an auto trans since you mention it has the neutral switch on the column. If it was originally an auto truck there should be two purple wires under the dash going into one two prong female connector. Since you cant find this, i would be willing to bet that you have a truck originally equipped with a manual trans that was swapped to auto or your wiring harness was swapped with one from a manual truck. Manual trans trucks have the neutral switch on the trans. Take a look under the truck in the trans tunnel area and see if you can locate any loose wires. If so you can route these into the cab and hook them to the neutral switch on the column.
Posted via Mobile Device

[72 K20]

Manual trans trucks have the neutral switch on the trans.

I have 2 '72 trucks,C20 and K20 both factory 4 speeds and all that's on the trans is the back up light switch. Don't think I have ever seen a neutral safety switch on a manual trans.

[WIDESIDE72]

Originally Posted by 72 K20

Manual trans trucks have the neutral switch on the trans.

I have 2 '72 trucks,C20 and K20 both factory 4 speeds and all that's on the trans is the back up light switch. Don't think I have ever seen a neutral safety switch on a manual trans.

Youre right i was thinking of the bu light switch!
Posted via Mobile Device

[Scottcoda]

I think that the truck has always had an auto tranny just b/c of the "low hump" in the cab, Although it may not be the orignal. Other than this bypass, the rest of the wiring is not a mess.. No birdsnests or after market crap that seems to clutter under the dash of 40 yr old trucks, I almost wish there was something left for me to trace so I would know where the wiring is supposed to go from the switch, nothing nada.. just a clean old truck with no working back lights and can be started in drive (not good)

[WIDESIDE72]

Not all manual trucks had the high hump. 3 spd trucks have low humps. "Bypass" would indicate the two purple wires for neutral switch had been jumpered. You are saying there are no wires present. I have no other explanation, other than

1. Keep looking for he two purple wires

2. the truck had a manual trans originally so no neutral wires in harness

3. Harness has been swapped
Posted via Mobile Device

[WIDESIDE72]

I double checked my 72 wiring manual and it is definitely a purple wire for neutral switch. Trace the purple wire from the ignition switch. If the harness is from an auto trans truck there will be a connector for the switch. If there isnt a connector, You can interrupt the purple wire coming from the ignition switch, so you have one wire from the switch and one from the bulkhead connector.and connect both wires to the neutral switch. This way the only way power will get to the starter is when the shifter is in neutral or park.
Posted via Mobile Device

[WIDESIDE72]

I am going to have to make this exact mod to my 72 swb stepside. The original harness was for idiot lights and it was cut up so i pulled it and installed a nice harness for gauges from a truck i parted. Only thing is i forgot that the donor truck originally had a 3 spd trans so i dont have a connector for the neutral switch.
Posted via Mobile Device

[Scottcoda]

Thanks for the input.. I have to agree the lack of wires would suggest just what Wideside said..harness swap or orginal manual tranny.
In New york state cars/trucks prior to 69 did not require back up lights so legally I dont require them but if the lights are on the truck they have to work so either I try to figure out how to get them to work or remove them from the truck

[WIDESIDE72]

So no back up lights either? Check under the truck by trans for back up light wires as mentioned above. My 72 manual shows these are dark green.
Posted via Mobile Device

[Scottcoda]

just got to take a peek around the tranny and no wires floating around the housing unit.. gonna try and follow the wiring back from the back up lights and see where it goes then maybe fiqure out how i can get the saftey switch back online
Posted via Mobile Device

[Bigdav160]

My automatic transmission truck ('72) has a combination switch.

Purple wires for the neutral safety and green for backup lights.

[Longhorn 70]

You could always trace the purple back to the ignition switch and to the starter solelnoid. Basically that wire goes from the ignition switch to the start terminal on the solenoid. IF you find that, run a wire from the start switch to the NSS terminal on top and the terminal on the bottom goes to the solenoid.