Temp gauge pegged

[Luva65wagon]

On the Comet, which is going to a new home on Wednesday (they will announce that themselves, I'm sure) I have been trying to debug the temp gauge all day.

Here's the history: It (temp) wasn't reading and neither was the fuel gauge. Once I changed the gas tank and sender neither gauges worked still, so I have a collection of constant voltage regulators (CVR) and swapped out a couple until the fuel gauge came to life. Still the temp gauge was COLD all the time.

So I did the checks and could peg the temp side if I grounded the sender wire. Gauge is good. So I checked the sender and it was open.

Got a new sender from NAPA Sunday and installed it tonight and now it will peg the temp gauge if I hook up the sender wire. Thinking I had a bad sender I had another from a later head (1/8" pipe). Hook it up and it pegs it too.

I have other instrument clusters of various years and hook them up one at a time and all peg.

So, this has me totally stumped. I'm pretty sure the sender is the right one (according to specs), but not able to find what cold resistance is supposed to be. I ran it under really hot (insta-hot) water and resistance was close to hot value. Cold is between 220 - 350 ohms on all my cars.

I know something changed in '63, but not sure what. The sender went to 1/8 pipe from 1/4 pipe and resistance was slightly different at 220 degrees:

1962
http://www.napaonline.com/Catalog/Ca...464_0162101090

1963
http://www.napaonline.com/Catalog/Ca...178_0162101093

Anyway I search high and low for an explanation to this phenomenon, but right now I am stumped. I have yet to pull a CVR from one of my other cars, but I have two that do nothing and 2 that do the same thing. I'm assuming the two that are working OK with gas gauge are working, but I will check the voltage output tomorrow. Got too dark to continue.

I know I'm usually the one to answer this sort of question, but maybe someone else may have other senders laying around I can test with - or something else to add. I may have to add temp gauge under dash. This is the last thing I said I would solve.