88-94 "Neutral safety switch looking unit" wiring

[KRS1]

Hey guys,
As I start to get information on the wiring of these of trucks I have learned that it has a mechanical neutral safety switch. I messed with the ignition key and it is true, it only turns in park and neutral. I wonder why they did this instead of the electrical switch?--ah well..

Anyways, there 2 connectors going into this neutral safety switch looking unit. This is how the wiring seems to go--

The blue green connector is for the backup lights, the green goes to the light and the blue is the power.

The one I can't seem to figure out is the "position sensor connector". These have a orange/black wires. What purpose does this connection serve? Is it linked to the transmission/fuel etc??

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[PlayingWithTBI]

Not sure but, it may be what tells the ECM that you're in D or OD?

 

[AK49BWL]

Not even the later Vortec GMT400 PCMs got those signals, the PCMs run off the internal pressure switches in the transmission.

I can't find anything about that switch setup in any wiring diagram from 88-94. There's no showing of a starter cutoff or neutral safety switch in any of them, I can't figure that out.

Then again I know some of the earlier models came with keyless entry and that's completely absent in all diagrams as well until 95. Either OnDemand isn't complete or GM never gave up the info.

 

[KRS1]

Hey guys, Yes, I had a hard time finding info on the wiring for this "fake NSS" lol . I even have all the books. Here is the ignition switch wiring diagram I made so far...I will likely leave that black/orange alone. the only purpose of the switch will be for backup lights. I am trying to link various pieces to a universal wiring kit..

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[AK49BWL]

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That's for a 94. Traced and verified.

Sw1 = Hot in Accy/Run
Sw2 = Hot in Run only
Sw3 = Hot in Run/Start
Sw4 = Hot in Start
Sw5 = One side grounds to the body, the other goes to the temperature gauge. It's a "Bulb Check" position that activates between Run and Start.

 

[KRS1]

Thanks Brandon! I think I read somewhere that the ignition switch is self grounding? So is that ground for the temp gauge? I think at least 2 of the tabs aren't of any use for me..here is the updated picture as well

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[AK49BWL]

You're reversed. Actually that's all broken. the pin you have marked ground is the pink Ign 3, your "hot in run" is actually to the starter solenoid, and the two silver-coated tabs are the grounding switch... Looks like you're right about the two ground pins being grounded by the switch body when in the bulb-test position tho.

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Also the pin I have marked ground in black may very well actually go to something on the 91-94, namely the brake warning indicator.

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The starter solenoid wire is yellow on manual trucks and goes to the clutch switch before the starter, purple on autos goes direct to the starter................at least according to the diagrams.

 

[KRS1]

Thanks! It all works, when I turn the key the IGN,start, accessory circuit operates! Here is a short video..

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[KRS1]

I installed the "NSS looking unit" you have to slide the yellow indicator in the slot..I cracked off the some of it off lol. I put the broken piece in and it still worked. I put power to the blue and shifted the column into R and my test light lighted up..

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[Bheard]

2024 now and here I am with an 88’ c1500 and the neutral safety switch isn’t working properly. Wants to fire in all gears. Any suggestions?