Question on replacing a temp sending unit on a 70 roadrunner superbird

[1970 birdman]

Hi everyone
my temp gauge stopped working and all of the others still work . I was going to replace the sending unit . Can someone tell me if I will need to drain antifreeze before removing the unit ? The engine is a 440 six pack

 

[440+6]

Yes you will have to drain the coolant to at least below that level.
But first test the sender by grounding the wire to the sender, then turn the key to the on position. The temp gauge should climb pretty quickly, turn the key off quickly. If the gauge works the sender is bad.

 

[1970 birdman]

Well tested the unit and the gauge did not move when I jumped it . Not sure what next step would be ?

 

[69a100]

Check that wire for a bad spot and fix it, retest again with a known good gauge. Not necessarily in that order, but it will give you a idea of what to do next. Good Luck

 

[Sixpactogo]

lift the wire off of the temp sender. With engine cold, I think you should read somewhere around 300-350 ohms with a digital analyzer. Black lead to engine ground and red lead to sender. If you read zero your sender is shorted. If you read much over 350 ohms, the sender is bad. Test the wire going to the gauge also. I don't know what you should read for resistance there but you should see some kind of resistance. Maybe 30-50 ohms. If zero, either the gauge or wire is shorted to ground. If you read nothing at all between the wire and ground, the wire is broken or the gauge circuit is open somewhere.

 

[1970 birdman]

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I am going to test the wire with the ohm meter can someone tell me the best way to get the purple wire out of the block on the firewall without damaging the wire ?

 

[440+6]

The wire is easily removed with a small screwdriver from the front (small tang that holds it in), but once you unplug the block from the bulkhead you can just test the wire from the block itself without removing the wire.

 

[1970 birdman]

Thanks one more dumb question to remove the bulkhead from the firewall to check the wire do I need to bend those tangs back or does the block slide out ? Once again sorry for the dumb questions wiring is not my strong point

 

[440+6]

You can test the wire without removing the bulkhead connector from the firewall, just put your probe on the terminal.
And yes if you bend the metal tangs inward the block will push into the cabin.