The Stovebolt Site Forums The Shop Area The Electrical Bay Temp Gauge Frustrations - 57 3100

Okay,

You know how hard it is to get all the little lights and plugs and speedo cable and oil pressure line and wires fitted to the back of your cluster, with only 1/2 inch of space to work with?

Third time for me chasing the same issue; A temp gauge that just sits on zero and stares at me.

I have replaced the gauge twice with other used ones (yes, I know that doesn't mean they work either, in spite of what the previous owner says). I have 12 volts at the terminal that goes to the ignition switch (the "C" side), and continuity between the "H" side and the end of the sender wire that connects to the sender.

At this point, I would suspect a bad sending unit, but here on the site, folks say that you should be able to get the needle to move if you ground the sending wire with the ignition on. Mine does not do that. Just sits there and does nothing. All the other gauges work.

I warmed the truck up for 40 minutes today to test the unit. Nada.

What am I doing wrong? I am tired of the four-hour process of removing the cluster, breaking the stupid cheap bulb housings that come on the wiring kits these days, and skinning my hands on the dash sheet metal.

Help is appreciated.

-Jim

have you checked any of the gauges on the bench? just need to hook a battery to + side and ground the other post to the gauge case, or hook a sender to it, and with the sender body grounded to the gauge case, suspend the sender in hot water .... sounds like you have a batch of bad gauges, or maybe you have used thread sealer or teflon tape on the sender threads?

Bill

Check sendor grounding
Only need a small hose clamp and length of wire. Use hose clamp to attach wire to sender connect other end to battery terminal bonded to ground.
See if that makes any differance

IF NOT
Get new sender and matching instrument. They must be a matched setup.

Hook up as described above on bench and get boiling water. Put water in cup and put in sender should indicate around 200. If you want to get really accurate and do your own calibration put in a thermometer. Add cold water for other temps and be sure to stir. Allow about 30 second for sendor to heat /cool before comparing to thermometer.

I have learned the hard way to ALWAYS check operation on bench before installation. Just because it is new seems to mean nothing in todays world.


Dan Bentler

"They must be a matched setup" = false, all 56-78 6 cyl = NAPA TS 6469 car or truck if the gauge is good

Bill

I did attempt to check continuity on the bench, but that's as far as I got. I did NOT use teflon (or any other) thread sealant on the sending unit.

Will do those tests next time I have it out.

AFTER I buy one of those laser thermometers...that will give my skinned hands time to heal up for the next round of scalping.

Not sure what it is with me, but I seem to have to buy three of everything before I get something that works; Three carbs, three fuel pumps, three coils, and now three temp gauges. Karma, I guess.

Thanks Bill and all.

Jim

Alrighty then...

SO now I have movement of the needle for some reason. When warm, and when I pull the parking brake to the locked position, the needle now jumps to "H" and stays there.

No wires touching the brake mechanism that I can see.

Ideas?

I'd suspect a grounding problem for starters, when you cinch up the park brake you're probably affecting cab grounding - is your battery ground directly to the firewall as original, and another ground cable from the proper place under the toeboard to the engine?

Bill

Assuming you are buying the correct sender. Assuming you are not buying a sender for an idiot light: The gauge is grounded by it's metal frame to the gauge cluster by contact and thru screws. These spots need to be clean shinny metal. Then there needs to be a dedicated ground wire or two to the gauge cluster rear plate mounting screws. This ground wire(s) must then be attached to dash or other good shiny place. The entire cab needs to be grounded to battery at the passenger side firewall stock grounding location (as Bill said) and that needs to be cleaned and wire brushed shiny also. The engine block, which the sender is screwed into, needs to be grounded to battery also. It is always advisable to be sure all the stuff works on the bench, FOR SURE, at several temp ranges before installing. That way you know the components are good and can concentrate on the wiring. This stuff is a real headache unless approached correctly from the beginning. Take off all the grounds and re-clean/sand/brush them as the next step and to help in future electrical part installations. Sensor is a TS-6. Parking brake? That beats the guy on here who has to turn on his blinkers to start his truck! As Bill58 says; you are creating a needed good ground...or are bending a wire in the right direction!?!?!?

Thanks Gents,

I agree that it's likely grounding. Suspected that the minute I pulled the brake and saw it jump. Looked for frayed wires and found none, so I will continue down that road. Out of curiosity, why would the unit peg all the way to "H" rather than work intermittently at lesser ranges?

I do have the battery neg terminal grounded to the firewall, a ground strap attached between the starter and right toeboard, and a separate 00 cable between the frame and cab.

Bartamos, you mentioned separate ground wires to the gauge cluster rear plate screws. I will try that, but did you have a specific spot that you'd recommend? I did try a test lead ground wire to the chrome part of the cluster before with no results, but I suspect I was not getting an adequate ground.

Also, I had not considered the "idiot light" sender issue. Since N_PA did not have a correct anything for my truck, I got a '66 sender (it matched up in all other respects to what I had), but I don't know how to tell if it's as you describe.

Again, thanks.

Jim

all 56-76 with a gauge use the same sender, some brands are TS6 as bart says, or NAPA# TS6469 - put the sender in a pan of water with test leads attached to the post and body and heat it up, see if resistance changes gradually or does a jump when the water starts boiling

Bill

The gauges are mounted to little plates and the plates are mounted to the cluster rear plate with screws. Use those screws or a perimeter screw. I have been fooled before, just touching a surface to test ground. Not enough contact most times. You can hang the cluster with string or wire from the steering wheel to work on it if you have enough "service loop" or create one. When sender wire is grounded is reads hot, maybe it is getting grounded somehow or you have a warning light sender, those senders are more of an on/off switch to light the light at a set temp. 1966 did have warning lights!!!!! I think Warning light sender has two blades and gauge sender has one stud terminal.

Got it. My sender has the single nail head, but was spec'd for a 66.

I'll do Bill's heat test when I have time to get my head into the engine bay next weekend.

Thanks for the help.

Jim

If you are goin in alone, we'll cover you from here. good luck.

For the archives I’d like to add to the chorus for checking grounds. I just had issues with a ’56 restoration and this post helped me track it down.

I added a 16AWG ground wire from the ground stud on the firewall to the instrument cluster itself, and “cleaned” metal where it was attached and where each part of the gauges screwed to the housing. The gas gauge worked fine but the temp gauge pegged. I jumped a ground wire to the contact on the back of the gauge itself (with gauge out of the housing) and it worked fine. So, I re-cleaned all the connection spots with a die grinder wire brush and that did the trick. They were clean metal before (considering age), no rust, but the temp gauge required a lot better ground to work than the gas gauge did.

The ground path for the temp gauge goes from the instrument cluster housing to the individual (or pair, in this case) gauge back panel to a little solder contact on the back of the individual gauge's circuit board. All these contact points need to be good.