More about temperature senders and gauges

Byron Warwick

Byron Warwick

Senior Member
I followed Old Henry's instructions to confirm the wiring of my temperature gauge. When I attach the right side sender wire to the left (Double) side sender, the gauge goes completely hot. My question is should I reverse the wires on the gauge? Thanks, Byron.
 
Byron Warwick said:
I followed Old Henry's instructions to confirm the wiring of my temperature gauge. When I attach the right side sender wire to the left (Double) side sender, the gauge goes completely hot. My question is should I reverse the wires on the gauge? Thanks, Byron.
Click to expand...

Gauge will read hot whenever there is no current running through it - just like when the key is turned off. The left sender does not complete the circuit to ground so will not deflect the gauge. It is just a "circuit breaker" of the circuit going through it to the right sender that completes the circuit through that sender to ground. It doesn't matter which wire is connected to which terminal on the left sender or if it's even there at all. You can short across the terminals or just connect both wires to the same terminal or connect the wires to each other skipping that sender altogether to eliminate it in the circuit to test to see if it's bad. Once you've done that all current is being controlled by the right sender and it is the only sender controlling the gauge.

Study the circuit from the temperature gauge through the two senders in the following wiring diagram to understand better:

WiringDiagrammiddle.jpg
 
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The Professor is correct. Here is a little more detail on the system operation.
 

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Not to hijack this thread, but I helped a buddy restore his '50 F1 and we are having issues with the temperature gauge. He replaced the flathead with a fuel injected 302 but his gauge panel is still factory. We put a factory flathead right side temp sender in the motor and we have a 6v reducer on the gauge panel. when you start the engine the temp gauge swings from Hot to Cold and then never moves. We've put in three different factory temp gauges in the truck and all of them do the same thing. Any ideas on how to get the temp gauge to work?

thanks
David
 
Hivolt5.0 said:
Not to hijack this thread, but I helped a buddy restore his '50 F1 and we are having issues with the temperature gauge. He replaced the flathead with a fuel injected 302 but his gauge panel is still factory. We put a factory flathead right side temp sender in the motor and we have a 6v reducer on the gauge panel. when you start the engine the temp gauge swings from Hot to Cold and then never moves. We've put in three different factory temp gauges in the truck and all of them do the same thing. Any ideas on how to get the temp gauge to work?

thanks
David
Click to expand...

Check the voltage going into the gauge to be sure that it is getting reduced to 6 volts by your reducer. Some of those reducers don't work. Anything over 6 volts will keep the gauge on cold.

Let us know what finally fixes it.
 
Hivolt5.0, your temp sender itself needs to be grounded to the block. You may have used teflon tape when installing the sender, and have no ground there. For a quick test, try an aligator clip test lead to ground from the body of the sender.
 
Hivolt5.0, You tried 3 different gauges and they all do the same thing. That is go to cold and stay there. Have you tried a different sending unit? These senders are not resistive. It may not be switching. Take a look at the diagram in my earlier post.
 
ford38v8 said:
Hivolt5.0, your temp sender itself needs to be grounded to the block. You may have used teflon tape when installing the sender, and have no ground there. For a quick test, try an aligator clip test lead to ground from the body of the sender.
Click to expand...

I don't remember if we put teflon tape around the threads or not but I'll definitely check that out.

41ford1 said:
Hivolt5.0, You tried 3 different gauges and they all do the same thing. That is go to cold and stay there. Have you tried a different sending unit? These senders are not resistive. It may not be switching. Take a look at the diagram in my earlier post.
Click to expand...

We have not tried any other sending units. The owner of the truck was trying to narrow down what the problem may be before he buys a new unit. The sending unit that is in the truck now came out of the original flathead and of course it "was working when parked". I'll try these other things first but he may have to buy a new sending unit.

thanks for all of the advice guys!!!
 
That is how everything is wired. Perhaps the right sender is faulty. I may have a spare. I think I removed the teflon tape last year. I'll try to switch the wires on the left sender before reversing the wires on the gauge. My gauge reads cold with no current, so maybe it is bad. Thanks, Byron.
 
Last week I finally had the opportunity to test the sending unit on my buddy's '50 F1. I tried grounding the case of the sending unit with a piece of wire but that didn't seem to affect the gauge, the needle didn't move off cold and I know the engine was at operating temperature because he had just driven to my house.

So last night I had another opportunity to check the voltage from the reducer. I measured 6.96 volts from the reducer. I also checked to see what the voltage was from the signal wire. With a cold engine the signal wire voltage was 1.24 volts. I'm not sure if the voltage changed with a warm engine, I wasn't able to stay long enough to check that.

Does any of this help lead me to resolve the temp gauge issue??

thanks in advance for your help.
 
If the gauge goes from hot to cold when the ignition is on the gauge is good. It really does not make any difference how the gauge is wired. It is basically a heating element wrapped around a bi-mettallic spring to move the needle. Your issue is the one teminal sender. It is no longer switching in relation to the engine temp. The contacts in it are stuck closed causing constant current flow, thus making the gauge indicate cold.
 
Thank you 41ford1! I'll let my buddy know he needs a new sending unit. He was going to the Moultrie, GA swap meet this weekend any way so he can pick one up there.
 
The gauges in old Fords are King Seeley brand. To check out the gauges, fuel, temp and oil pressure, use a "D" cell battery and hook wire off sending unit to + or - and other end to ground side of gauge. Should read half scale. Hook two "D" cells in series and gauge should read full scale.
As for your voltage reducer, THROW it away! Put on what Ford used for years. Ford used a voltage reducer on their gauges and think it is a VR-1 at NAPA. Hope this helps.
 
Disconnect the wire at the sending unit gauge should now go to hot with the key on. if it does it is an issue with the sender if not the problem lies in wiring or the gauge.
 
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