90 GMC 2wd-4wd IFS conversion project wiring SNAFU

[old school truck dude]

      I do believe I have run into a situation with the wiring of this thing. The 2wd cab "appears" to have some connectors that do not match up with the 91 4wd motor. I never wouldve thought there would be any difference! I say appears because I could very well just be lookin at things wrong or cross-eyed but it seems like somethin aint right, and Im not real sure how to proceed. I DID save the complete engine wiring harness and computer from the 91, the cab Im usin is a 90 2wd. I had the thought to just throw the 91 4wd harness on it, but who knows if the pins are lined up anywhere similar on the 2 bulkheads where they go through the firewall on the drivers side. Could short it all out and burn the truck down, ya know. Im pretty sure the 91 4wd harness will not work as the part where the computer wires go through the firewall on the passenger side - that plastic grommet thing - its completely different. Im tryin not to do a "hack job" on this, the theory was to make my truck into an ext cab 4x4 and spend as little as possible. I do have a 1976 350 carb motor sittin on a stand complete and ready to rock, that would solve the problem but Id prefer to have the TBI in it as thats whats supposed to be in there.

[ToughBowtieTruck]

I think the connectors would be related to the 4 wheel drive harness that goes into the cab for the fuse, 4wd light on the floor, and the other wires for the transfer case . . . There wasn't a whole lot changed from 90 to 91, If I remember 91 still had the same dash gauge cluster as the 88-90 . . .

[old school truck dude]

Yup. thats what has me confused, I got a couple connectors that go somewhere around the throttle body and nowhere to put them that I can see, and one I think I know it goes in the pass side of the throttle body might be the IAC but its shaped a little different and wont fit. Again, I might be lookin at it wrong, but I been starin at it for "a while" now hee hee

[ToughBowtieTruck]

Some might be for A/C or smog pump . . . some trucks have extra connectors hanging around that never got used if the trucks weren't installed with smog . . .

[Mudbuster]

they did use a  couple different throttle bodys in the early 90's pics would probobly be more helpful

[old school truck dude]

I cant find a connector on the 90 2wd harness for this

Some more pics

[ToughBowtieTruck]

1st one is the sending unit for the Oil Pressure switch.

http://www.autozone.com/autozone/parts/Duralast-Oil-Pressure-Switch/1990-Chevrolet-C1500-1-2ton-P-U-2WD/_/N-igjdrZ8znc6?counter=1&filterByKeyWord=oil+pressure+switch&fromString=search&itemIdentifier=19005_0_0_5673

[ToughBowtieTruck]

3 wire flat prong sitting by injector rail is the old style throttle position sender unit.
That's the sensor on the throttle body you're "not sure where this goes"


http://www.autozone.com/autozone/parts/Duralast-Throttle-Position-Sensor/1990-Chevrolet-C1500-1-2ton-P-U-2WD/_/N-igjdrZ9gsmg?counter=0&filterByKeyWord=tps&fromString=search&itemIdentifier=172783_0_0_

[ToughBowtieTruck]

The two wire female plug you have on your hands, what colors are the wires ?

[Mudbuster]

The two wire female plug you have on your hands, what colors are the wires ?

looks to me like one of the A/C pressure switches.  You are right on the rest of them

[BigFrank]

theres a throttle bodts of 2 engines over here if the sensors will work ya can have em    i think the one has the plugs hooked to it   ill look when i get out to the barn

[old school truck dude]

Ok havent been able to get back out there to it, been one thing after another, pc was down for a day, lemme go look n see what I got now that Im armed with new knowledge

[old school truck dude]

The two wire female plug you have on your hands, what colors are the wires ?

Dark green and light green, it does appear to be the A/C pressure switch, no A/C on this rig, the compressor will be a tire pump eventually.

[old school truck dude]

theres a throttle bodts of 2 engines over here if the sensors will work ya can have em    i think the one has the plugs hooked to it   ill look when i get out to the barn

Cool!

[old school truck dude]

Im guessin I can just change the sensor here on this? Looks like the temp sending unit.. Its on the drivers side head

[old school truck dude]

And then there is this jewel, where does it go? Im guessin I will need to change the throttle body to one for a 90 2wd..? I have figured out some of this with you guys help, so Im goin back through the thread and gettin rid of whats figured out and done to eliminate some confusion (on my part most likely)

[old school truck dude]

1st one is the sending unit for the Oil Pressure switch.

http://www.autozone.com/autozone/parts/Duralast-Oil-Pressure-Switch/1990-Chevrolet-C1500-1-2ton-P-U-2WD/_/N-igjdrZ8znc6?counter=1&filterByKeyWord=oil+pressure+switch&fromString=search&itemIdentifier=19005_0_0_5673

Got that plugged in now, thank you

[old school truck dude]

3 wire flat prong sitting by injector rail is the old style throttle position sender unit.
That's the sensor on the throttle body you're "not sure where this goes"


http://www.autozone.com/autozone/parts/Duralast-Throttle-Position-Sensor/1990-Chevrolet-C1500-1-2ton-P-U-2WD/_/N-igjdrZ9gsmg?counter=0&filterByKeyWord=tps&fromString=search&itemIdentifier=172783_0_0_

Im startin to think this is the one that isnt matchin up, would it be plugged into the throttle body if I had the correct throttle body on there?

[ToughBowtieTruck]

3 wire flat prong sitting by injector rail is the old style throttle position sender unit.
That's the sensor on the throttle body you're "not sure where this goes"


http://www.autozone.com/autozone/parts/Duralast-Throttle-Position-Sensor/1990-Chevrolet-C1500-1-2ton-P-U-2WD/_/N-igjdrZ9gsmg?counter=0&filterByKeyWord=tps&fromString=search&itemIdentifier=172783_0_0_

Im startin to think this is the one that isnt matchin up, would it be plugged into the throttle body if I had the correct throttle body on there?

Yeah that's the one you showed the pic of. Supposed to plug into the sensor on the throttle body (the one you don't have a plug for).

You could splice the new style throttle position sensor plug too to match the newer throttle body. Just make sure you make good weatherproof connections. And just match the colors, you have a power, ground, and resisted power. (the resistance wire is how the computer tells how open the throttle plates are. and the wire you use to test for a bad sensor.)

The other one, by the cylinder head, yes that is the old style temp sender wire for the gauge. The new style sender in the head is the weatherproof version. It is also a single-wire. Easy cut and splice the other connector.

[RIP_K52007]

I dont think the sensor will swap over.. they wont from full size to s10, one hooks to the throttle plate shaft different than the other. Probably have to just run the style TBI unit that your wiring harness is for...    but then again... i could be wrong ....   LOL