Two Connections - What for?

AuroraGirl said:

oh maybe im right then

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That was one I asked about awhile ago. All my wiring is so butchered I bought a complete new setup from Painless. Keeping the proprietary pigtails to integrate when it all goes back in.

Scott91370 said:

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Doppleganger said:

This is probably a mile off, but that round black one looks identical to a pressure switch for AC.

I had a similar plug on mine that after dissecting the truck I found it to be related to the tank switching solenoid.

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The black round one in this pic is for the pressure switch ion the TH350C transmission. Still don't know where the red one goes but I'm sure it is cruise or trans related since they're all fed off the same 2 wires.

Doppleganger said:

That was one I asked about awhile ago. All my wiring is so butchered I bought a complete new setup from Painless. Keeping the proprietary pigtails to integrate when it all goes back in.

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I don't have my truck but I know mine like that is hooked up. When I get it back I will try and remember this post so I can answer the question.

I found this diagram on another page ( http://67-72chevytrucks.com/vboard/showthread.php?t=217155 ) - if cross posting isn't allow I understand.
I just can't tell what the wiring is for the red plug - or what vacuum source it should go to.

My notes are in red.

I would thi k there is a switch that uses vacuum to determine if cruising

Found this

The other side of the vacuum switch consists of a male vacuum connection which I tubed to the intake manifold vacuum tree. The small check valve was inserted between the switch and the manifold.

The wiring should go to the switched 12 volts from the brake switch for the lockup(to unlock when you hit brakes so you don't stall)

With that info and the other stuff I am going to bet I will not find the vacuum source on this truck because the body is from an 85 which did have the 350C but the frame/engine/trans are from an 82 that has a 700r4.

THANKS!!!


Now to find a nice way to tuck the wiring away so it can't be seen but not cutting it. Not that I will ever go back, if anything it will go LS...

frm left to right. oil sender on driver side of block near exhaust?, esc throttle tip in switch is the red one-plugs into vacuum switch on dash next to ac components, 700r4 4 pin connects at trans on driver side. At least thats what mine are and I have the engine out right now on the 84 305/700r4

Swearbody said:

frm left to right. oil sender on driver side of block near exhaust?, esc throttle tip in switch is the red one-plugs into vacuum switch on dash next to ac components, 700r4 4 pin connects at trans on driver side. At least thats what mine are and I have the engine out right now on the 84 305/700r4

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Left to Right:
TH350C Pressure Sensor on passenger's side (black round)
Unknown vacuum source with 2 nipples on it (red rectangle)
350/700r4 Lock up on Driver's side (white square)

The vacuum switch on mine are connected and it is a black rectangle plug. That plug is part of the Electronic Spark Control System (has the below connections as well) and isn't used if you have switched over to HEI.

Scott91370 said:

Left to Right:
TH350C Pressure Sensor on passenger's side (black round)
Unknown vacuum source with 2 nipples on it (red rectangle)
350/700r4 Lock up on Driver's side (white square)

The vacuum switch on mine are connected and it is a black rectangle plug. That plug is part of the Electronic Spark Control System (has the below connections as well) and isn't used if you have switched over to HEI.

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The round one as you said for the trans.....I can see that now( a bit different looking than the oil switch)

I know for a fact the red 2 prong is a tip in vacuum switch that was tied into esc through the egr and air breather
Also I agree the 4 prong is tc lockup for a 700r4
The 4 pin in this pic is esc control like you said but the other I dont recognize

I just went through all this on mine and did a video on the esc delete. I am not sure which vac switch you are referring to being hooked up...trans vac control? I see that i your diagram. I am referring to the red one(unknown) you didnt know where it went...Thats the tip in.

I not sure if you are agreeing with me or saying something otherwise??

I can get some pics if it will help. I am trying to help i promise.

On my esc delete video you can clearly see all of those connections regarding esc. Right at the beginning of the video about 1:20in
The red 2 prong connector is on the engine passenger rear. Controlled egr i think

Swearbody said:

I not sure if you are agreeing with me or saying something otherwise??

I can get some pics if it will help. I am trying to help i promise.

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I am agreeing, I think we were both reading slightly wrong. I pulled all my ESC stuff out since I have HEI now and I am going to guess I could just as easily cut the red plug and the black plug out since I am switching from the TH350C to a 700R4 - I'm just trying to keep the harness without any exposed/cut wires.
I have a feeling the wire that you mention in your video that goes to the knock sensor is a purple-ish one that I took out with the rest of the ESC wiring.
If the red plug is for EGR I definitely don't need it.

Thanks for the input!!


I see your carb has 3 vacuum lines connected on the front - mine are all capped. Can you tell me what each go to?

facing the carb the left is manifold vac and i have my vac advance hooked up there. The big one in the middle is pcv, the right is ported vac and mine is hooked to the tc vac switch

I was debating cutting out that part of my harness as well. I left it in place for the moment but since i just painted the engine bay I may as well cut that crap out. I too have been learning what can and what cant be deleted. Once I have the TC lockup working ill be deleting some more. These trucks with the esc,700r4,and ecarb would be a nightmare without GMSB support

PERFECT! I'll be using the left & right. Seems someone stole my PCV valve and put the breather on it.

THANKS!