What the heck is this stuff????

[indyracer]

I can't find this on the wiring diagram. What is it?




This green wire is on the passenger side. There is what appears to be a sensor in the head down there. If it was on the drivers side I would call it a temp sensor.




Here is the green wire for the temp sensor on the drivers side.





Now these blue and black wires go to a plug on the passenger side of the carb. What are they???




Here is the plug.




Well, these are my questions of the week. I hope my pictures are good enough to see what I am talking about.

[Rupdog]

can't tell if the pigtail next to the carb goes into it, or where it goes. only thing i can guess on the passenger side of the engine is maybe an engine block heater? do the wires connect to anything, or just hang there?

maybe they're A/C connection? that is definitely a circuit breaker, used for high-load electrical, such as A/C, etc...

[Down south truckin]

some of these trucks have 2 temperature sending units. my 72 super has 2 i really don't know why or which ones have it or don't but some do ? and the other one looks like a/c wires

[Big D]

My 70 GMC with a 250 six has the same thing on the firewall. The red wires disconnected. I 've never chased down the wires but there was a solenoid on the carb that the PO disconnected. I'd guess it was to bump up idle speed. My truck never had air, Does yours? I seen to recall a lot of old F*rds having a device to crank up the idle speed when the air was on.

[indyracer]

No air on this truck. The 2 wires with the plug have a bracket connected to the intake that holds them.


Also, the red wire pointed out in this picture...



Is the red wire pointed out in this picture...





I also am pretty sure that the green wire in the first picture going to the breaker is the green wire that goes to the sensor in the head on the passenger side. I am going to do some more tracing this weekend.

[indyracer]

Okay, since I am removing the engine from the truck, it gave me a chance to look closer at this section of wiring. This wiring only consist of the wire that comes from the firewall by the fusebox, the wires from the breaker type connection to the plug on the passenger side of the carb, the wire that goes to some sort of sensor on the passenger side head and a wire that goes to the transmission. It kind of appears that it was added later, but the tape around the wires has orange paint on it like it was there from the factory. I am a little confused...

[bouncytruck]

My 72 has the same plug next to the carb, but it isn't connected to anything either. I've looked for where it should connect, but I haven't found it yet. Let me know if you figure it out.

[68C15]

for some strange reason I think it all has to do with electric overdrive transmission controls.

[OLDCHEV4X4]

Transmission controled spark advance. Does the sensor bolted to the intake have vacume advance hoze going to it or a place for hozes to go to it? If so thats what it is.

[Stoney]

It engages the A/C compressor to keep the engine from dieseling when you turn the key off. And the other is to idle the engine up when the A/C is turned on. Mine still work today.

[jkaylor68gmc]

A relay maybe?

[indyracer]

I am starting to lean towards the transmission controlled spark advance. I saw a harness on a vendors website and that clued me in. There is a vacuum hose that goes from the manifold to the transmission, I don't know if that is what you are talking about.

[OLDCHEV4X4]

That hoze is for the vacume modulator on the trans. The hoze i'm talking about would be between the distributer and the carb. The sensor would be inbetween the two with a line coming in and a line coming out. Sometimes they are eliminated and all thats left is the wires and relay.

[indyracer]

Could have been eliminated. My vacuum hose from the distrubutor and the carb is one piece.

Another question is what does "transmission controlled spark advance" do and since it seems it wasn't connected to anything, can it be removed?

[bouncytruck]

Originally Posted by Stoney

It engages the A/C compressor to keep the engine from dieseling when you turn the key off. And the other is to idle the engine up when the A/C is turned on. Mine still work today.

Can you post a pic of where it plugs in?

[ERASER5]

The wiring pictured is definitely the TSC system.

Originally, the two-wire plug close to the carb went to a vacuum switch that interrupted the vacuum advance.
The relay on the firewall was controlled by both a temperature sensor in the right head and a pressure sensor in the transmission. The temp sensor closed if the temp was above 32° F and the pressure sensor checked for third gear. In order to get vacuum advance, the engine had to be warm ( not freezing) AND the transmission was in third gear.

Now that you know WHAT it is, you can happily yank the wiring out and use the keyed hot wire for your new electric choke carb like I did.

P.S. I found this out just like you did right here on the board.

[indyracer]

With further research, it seems this is an emissions control thing.

To that I say, We don't need no stinking emissions control...