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Discussion Starter · #1 ·
My 1971 chev. 350 has a temp sensor that has one terminal. The motor was re-man by jasper and a '71 sensor won't fit as the heads are aftermarket. I was told by Jasper to use a sensor from an '87 350. The connection that went to the original block was cut. I am left with one wire with two terminals. one solid green and the other is green with a white stripe. What do I do with a one terminal sensor and two wires????
 

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Discussion Starter · #3 ·
Car has an idiot light only. When I ground the solid green wire the temp light comes on. I connected it to the sensor. What do I do with the other wire?? Leave it disconnected and tape it off???
 

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Dennis,
I don't know which is which, but it does make a difference, and it makes a difference which green wire connects to each of the terminals of the temp sender. One of the green wires goes to the temp light and the other goes to the TCS relay. Find the TCS relay on the firewall (it will have 3 connectors) and see which green wire goes to it. That's the one you don't need if your TCS is disabled. The TCS also consists of an elec solenoid, with vacuum connections, which is mounted on the intake to the right of the carb. The TCS solenoid has 2 wires going to it. One goes to a switch on the tranny, the other goes to the TCS relay on the firewall. The relay, which as I said earlier, has 3 wires. Also, as mentioned earlier, one goes to the temp sender and the other to the inside of the car for power.
Anyway, check to see which green runs between the TCS relay and the temp sender because you don't really need it (unless you have a correct factory restoration which includes the TCS system)
Also, the 2 connectors on the temp sendor
work opposite from one another. One terminal is grounded when it is cold and the other terminal is grounded when it is too hot. The one that is grounded when it is cold is the terminal for the TCS wire. When the sender senses operating temp, neither terminal is grounded.
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Tom Parsons

[This message has been edited by DZAUTO (edited 01-06-2000).]
 

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Tom- what don't you know???? Your reply about the wiring of the temp sending unit got me thinking. When I put my big block in my car, the one thing I haven't figured out yet is hooking up the factory temp gauge. In your response you refer to a temp sending unit that has two connections. Do you know if big blocks used two seperate sending units? I was told they did. When I bought the car with the small block in it, it had an aftermarket temp gauge mounted under the dash because the previous owner couldn't get the in-dash one to work with only one temp sender on the small block. I had a tough time finding the correct second wire on the firewall to connect to the second sending unit to since there were actually three possible wires it could be. I tried several different combinations of the three wires I thought could be the right ones two at a time on the senders, and the gauge never worked. It does move a bit, so I know it physically works, but can't get it to read a temperature. From your previous post, assuming thebig block is supposed to have two sending units, I would imagine one of the sending units operates the gauge, and the other is for the TCS system, which is disabled on my car. Where do the sending units go? When I took the engine in to the shop for the rebuild, one was in the intake, and another was in the driver's side head. Which one is supposed to operate the gauge? Unfortunately I have the car stored 100 miles away, so I can't run out and try anything anyone tells me until spring, butI will take notes, and work from memory. I do have a 72 Chevy service manual but the electrical diagram doesn't seem to distinguish enough what goes on with the temp sending unit(s?) Any help would be greatly appreciated.

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Steve

72 Chevelle SS402/4sp
 

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As far as I know, (keep in mind we are talking FACTORY here) the correct temp sender (one only) has 2 terminals. My cars, plus, the wiring diagram supports this. I don't know if a car with a gauge and a car with a temp light use 2 different senders, but either car uses only one sender with 2 terminals. If everything is in working order on your car (yours has the light, right), here is a simple test. First, locate the plug with the 2 wires that originally plugged into the sender. Get a short piece of wire for a jumper. Start and let the engine run. Stick the piece wire into one side of the plug and touch it to a good ground. Have someone look at your dash to see if the red temp light comes on. If it doesn't, then ground the other wire. As you look at the end of the terminals on the sender, they form a V. The wire for the temp light SHOULD BE V< on this side of the V. The terminal on this side >V, SHOULD go to the TCS relay. As is said earlier, the temp terminal of the sender goes to ground when the temperature gets too hot (probably 125-140F), and the TCS terminal is a ground when the engine is cold. A simple test for this terminal is to use a test light. Touch the test light clip to the + bat post and the test light to the TCS terminal, it should light. Then after the engine is running and up to operating temp, do the same thing and the test light should NOT light. TOO EASY.
I have relocated the sender on my 70 to the intake manifold because the headers get too hot for the plastic connector. And I have completely disconnected/removed ALL my TCS stuff to help clean up under the hood.
Hope this helps.
All of the above should also apply to a car with a gauge. Except with a gauge, when you ground the temp wire, the gauge should go to full hot.

I WOULD ENCOURAGE EVERYONE TO INVEST IN A WIRING DIAGRAM. They are too cheap and are a very helpful tool.

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Tom Parsons

[This message has been edited by DZAUTO (edited 01-08-2000).]
 

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DZ- I'm trying to figure this one out too...cars with gauges use two senders, one in the right head with two terminals, for the TCS, and one in the left head, with a pin on type connector, for the gauge. (this is for '70)
Cars without gauges, according to my engine harness, still use the right head for the TCS, but the wiring in the front light harness for the temp light looks greek to me. Ny new front light harness has a two prong connector like the TCS, but with only one wire in it. Plus another green wire (without the insulation) which I have NO idea what it goes to. (I DO have the wiring diagram
)
I am going to e-mail 260 to see if his car has lights or gauges to see what his setup is.
 

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Discussion Starter · #9 ·
Gentlemen: I have learned that the '71 Chevelle has a temp. sensor with two terminals. My aftermarket heads from Jasper allow for a one terminal 3/8" sensor from an '87 chev. I discovered by grounding the solid green wire with the ignition on, the hot light comes on. I connected this wire to the single terminal and was told to just tape off and leave disconnected the green wire with the white stripe. I guess I'll find out if this works if the car ever overheats. HA Dennis
 
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