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Carcheologist
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-- 03-29-2022 @ 5:28 PM
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I want to set up and test a '40 temp gauge and temp sender on my workbench but need some help - which terminal on the gauge receives power and which one is ground? Photos from the back side of the gauge are welcome and appreciated!! 
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kubes40
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-- 03-29-2022 @ 6:05 PM
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Does this help?
Mike "Kube" Kubarth
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Carcheologist
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-- 03-29-2022 @ 6:29 PM
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Kube to the rescue!
From the back, the temp gauge is on the bottom right side? The copper strip is ground making the other terminal power, correct?
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TomO
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-- 03-31-2022 @ 8:24 AM
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The copper strip is a connection for the power or neg battery connection. One wire powers 2 gauges.
The outside of the sending unit is grounded or battery + connection. The wire to the sending unit is connected to the gauge terminal without any other connection. The sending unit will pulse at a rate that indicates the temperature of the coolant.
Tom
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Carcheologist
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-- 04-02-2022 @ 7:57 AM
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Tom,
Very helpful info, thanks. The problem with my current sending unit (on the engine) is that the gauge's behavior is very erratic, for example; at times the needle seems to indicate temperature correctly by moving from the HOT side of the gauge when the ignition switch is in the OFF position and advancing slowly to the COLD side of the gauge when the ignition is switched ON and proceeding to register temperature accordingly as the engine warms up. At other times, when I turn the ignition switch to ON, the needle advances RAPIDLY to the COLD side of the gauge and remains there even after the engine warms up. I don't understand what is causing this. Any ideas?
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carcrazy
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-- 04-02-2022 @ 11:52 AM
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Are you sure all of the wiring between the sender and the gauge is in sound condition and that the connections are free of corrosion and tight. Be sure the ground path is good. The sender should be scr*w*d into the cylinder head without any sealer or Teflon tape to ensure a good ground path. The ground wire (braided cable) between the engine and the chassis need to be in good condition and properly secured.
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Carcheologist
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-- 04-02-2022 @ 12:54 PM
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carcrazy,
I believe all the connections are clean and tight with no corrosion problems that I can see. The sender is scr*w*d into the head without thread sealant or Teflon tape, so should be getting good ground. I don't know what else to check.
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TomO
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-- 04-03-2022 @ 9:16 AM
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The sending unit provides the grounding for the temperature sending circuit. In normal operation the sending unit pulses and the current flow in the circuit moves the needle on the gauge. Some aftermarket sending units use a resistance to replace the pulsing sending unit. The resistance changes with temperature, the hotter the coolant, the more resistance moving the needle towards the hot side of the gauge.
It seems like you have an intermittent short circuit to ground in the wire to the sending unit or in the sending unit. Make sure that the sending unit wire is not shorting out where it connects to the sending unit and is not frayed where it comes across the motor or pinched where it comes out of the cover on the firewall.
I would look for an original KS sending unit. Check with vendors that have NOS parts and advertise on this web site for one.
Tom
This message was edited by TomO on 4-3-22 @ 9:19 AM
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Carcheologist
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-- 04-03-2022 @ 6:06 PM
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I can always count on good advice from all the guys here on this forum. Thanks for the helpful tips. I'll be checking everything as discussed. I'm sure I'll find the culprit.
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Carcheologist
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-- 04-08-2022 @ 6:10 PM
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Fiddling with the temp gauge issue again today. After starting the car, I noticed the temp gauge needle travel rapidly toward COLD again. I decided to reach behind the gauge to see if perchance I had a loose wire connection. Lo, and behold; one of the nuts on the back side of the gauge seemed slightly loose, and when I twisted it, the gauge started to work correctly. Whadda ya know? Just when you think everything is as it should be...
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