My 72' has two temp senders. One is on drivers side, with single blade wire tab, the other is on passenger side toward the rear. It has a two blade wire hookup. The tabs run at right angles to each other, not paralell. The drivers side was hooked up, the passengers side was not.  What wire or plug goes on it, and what does it do?   THANKS   Mark

Pass side sensor is for the TCS(Transmission Controlled Spark) system. This system allows/blocks vacuum to the distributor advance. There is also a timer located on the firewall that delays the application of vac. for about 20-30 seconds. The signal for the system comes from the transmission...on the automatic, it operates in 3rd gear only. On the 4 speed, it operates in 3rd and 4th gear.
What it does is delays the vac. advance to the distributor until the car is in high gear. It's part of the emissions requirements...

It depends on how much of the rest of the system is still there, and hooked up. If the other components are there, but the temp sensor in not connected, then the distributor may never be getting any vacuum when it should. You could follow the vac line from the distributor to see where it goes. It should go to a solenoid bolted to the front pass side of the intake. If it goes directly to the carb, then they TCS system has been bypassed.
I think I have a schematic of the earlier TCS system, but I'll need to dig around some. In the meantime, I know this subject has been discussed here in the past, so a "Search" may bring up a thread/post that describes the complete set-up, and how it functions. Different year models, and engines used slightly different components, too. For instance, my '74 is only set-up to work the system in 4th gear, where the earlier cars work it in 3rd and 4th. Some '74s also did not have the timer set-ups. This was some of the early attempts to comform to the Gov-ment regulations on emissions, so some of it was pretty much hit or miss. 
Adams' Apple2010-02-22 21:19:24

This is a new lesson for me. Never saw this set up. The sender is in the block/water jacket. The vaccume line for advance is a direct hook up to the carburator. The advance works when needed, as I replaced it due to a performance lag, and made a considerable difference in pizzaz. If this is a block only when A/C is on I have not tried that.  The solenoid you speak of is not there, and no brackets for it. Could this car be a MISS on the attempt for emissions?  I will do some more home work and see what I can dig up. The carb is a Q-jet, and the only thing on that side is the choke coil reset on intake.   THANKS  Mark

[QUOTE=manchestershark]The sender is in the block/water jacket.[/QUOTE]

In the block, or the head??? If you have something in the block itself, where one of the freeze plugs would go, that would be a block heater, which was an option on cars sold in the North, where it gets a wee bit chilly. If it's in the head, then it is the sensor for the TCS.
Got pics?

From the sound of it, your TCS has been totally removed. If you're trying to put it back all "original", some of the parts may be hard to find, or really expensive if you can find them. If you're just wondering what the thing is, that's a different story.
I'm still looking for pics and descriptions of the TCS system.

Joel is right.  The original TCS system included a temp sensor in the right side head, which you still have; a switch in the transmission side cover, which is probably still there, as it was built in; and a solenoid valve which mounted between the distributor and carb.  The valve is available in repro for about $90.00.  Then you just need the wires, which are available, and vacuum lines.  It doesn't make your car run any better, but is correct.

Larry

 BOTH sensors/plugs are in the water jacket. Left one is for engine temp guage, single tab electrical. The right one was not hooked/no wire, up. BOTH are brass with phenalic black center and brass tabs for wires.  They both look the same, save one has two tabs and one has one. The wire I found loose has a mud wasp plug in it and is in the braid from the A/C. I am thinking the two must be mated, but do not know thier purpose.  NOT interested in a CORRECT/spec car, just want to hook it up if necessary. I looked at a 75 and a 76, they both have a plug with a square hole for a 3/8 drive extention or ratchet to remove it. They are definatly not in the soft plug holes.  Not looking to beat a dead horse, just want to figure it out.  If it is not necessary I will just put a plug in it. All I have is what is there.  THANKS  Mark

Since the rest of the TCS sytem is MIA, just leave that plug unplugged, and hide it if ya want. It will not hurt anything to leave it unplugged.
As a bit of info, the sensors do look similar, but have different connectors, as you state. However, they do NOT operate the same. The TCS sensor is kind of a 3-way sensor. It is basically an "Open/Closed" type sensor, instead of the thermistor type sensor used for the gauge. The TCS sensor allows for vacuum to the dist on a cold start for a short period of time, regardless of what gear the trans is in. Then it goes into "gear specific" mode, only allowing vac when in 3rd & 4th gears. IF the engine gets too hot, the sensor will allow full vac to the dist at all times, until the engine temp comes down to a "normal" operating range.
Adams' Apple2010-02-23 21:20:00

  MORE INFO. I did some home work in the Mid-America assembly manual. I found the switches, both of them. The info the guide gave was only for the LS-5 and LS-6. Does this also apply to the LS-3?  I have the switches in the proper places, but no wires. There is also no AIR pump,solonoid, spark tube or other smog stuff.  I do have A/C if that makes a difference. The carb does not have a solonoid on it either.  The wire I found is not the one for ths TCS switch, wrong plug. Removed the mud from end.  THANKS for the input, I am going to leave well enough alone and hook up what I have for asthetics and forget the rest.  The car runs well so I am happy.   Mark   manchestershark2010-02-24 08:47:16