Temp gauge not working

[72hoopti]

I put in a new sending unit on my 72. Ran new wire from passenger side to drivers side and got nothing. Gauge is pegged to cold.
Tried grounding wire to block and nothing happened. Read older posts about sending units being bad out of the box but hate to go through the antifreeze by pulling out the new one I just put in. Got power to the back of the temp gauge as well.

Any suggestions?
Posted via Mobile Device

[TBONE1964]

Why did you replace the sending unit in the first place and did it change anything? I would think you might have a problem with the gauge itself.

With the wire unhooked from the sender the gauge should read full cold. With the wire grounded, it should read full hot. If the gauge does not move when you ground the wire, the wire is open somewhere between the sending unit and the gauge or the gauge is bad.

[BruthaMan]

You would be lucky to get a temp sending unit out of the box that actually worked correctly.

I spent a great deal of time last week, researching this for my '78. It always showed quite a bit warmer than what the actual temp was. I had been chasing what I believed was overheating issues, but was actually incorrect sending unit output.

Seems like the Corvette guys picked up on this years ago, from my research, and one of their vendors had some sending units developed that are accurate for the older gauges (60s and 70s GM).

Lectric Limited makes correct sending units for our older trucks with accurate ohm output for proper gauge temperature reading. I ordered one last week, hoping it will be in this week as I near finishing up the build.

Hope that helps. I doubt it's anything you've done wrong. My understanding is that all the modern temp units from the auto parts stores have this same issue. You can find NOS temp units on Ebay...for an arm and a leg!

[beetle1960]

Originally Posted by BruthaMan

Lectric Limited makes correct sending units for our older trucks with accurate ohm output for proper gauge temperature reading. I ordered one last week, hoping it will be in this week as I near finishing up the build.

Let us know how the one from Lectric limited works.. I have been struggling with same issue for months, later model 350 with 3/8" npt sending unit hole...I have gone thru 6 different ones, even resorted to getting one from Summit that they said was for our year (3/4"), purchased a 3/8" npt pipe die, spun the sending unit in my lathe down to 3/8" size, threaded it, stuck in the hole, only to peg out hot. read here somewhere that a specific Ford unit was close in olms..tried it..pegged. finally said f it and stuck an after market temp gauge below the dash for now.

72hoopti...don't mean to highjack your thread..thought an answer to this would help us all with this issue.

[TacBlade]

Tagged for reference! I am having this problem also?

[67swb72klb]

i just went through this with my black truck
hope this helps

[68shortfleet]

I ran into this last summer of the gauge reading full hot. It turned out to be as noted in the picture above that the bottom lug on the gauge needs grounded to the mounting tin and the tin must be grounded to the back of the cluster.

When not grounded, the gauge goes full hot.

[72hoopti]

I took out external gauges that were hooked up when I bought the truck. I like the look of the gauges and want them to function. Amp gauge, oil, and everything works besides the temp gauges.

[72hoopti]

67swb,
you have to run a ground wire from that bottom post to make it work?

I have another 72 and that is not the case. And yes, the temp gauge works in the truck

[72hoopti]

no worries beetle

[BruthaMan]

I will update this when the sending unit from Lectric Limited comes in and I get it installed/tested. I'm hoping it will be in this week.

All that remains is a power steering bracket and pulley, and it will be ready to start/test. I should be able to get that done before it gets here, so that all I need to do is add it in and test it.

[leddzepp]

I have had to run a separate ground wire for the temp gauge on almost every cluster I have owned.

[72hoopti]

leddzepp,
so you are saying run a ground wire from the bottom prong of temp gauge to body of truck somewhere? Never seen this in my life and owned 6 67-72 trucks. Willing to try anything at this point.

[leddzepp]

Originally Posted by 72hoopti

leddzepp,
so you are saying run a ground wire from the bottom prong of temp gauge to body of truck somewhere? Never seen this in my life and owned 6 67-72 trucks. Willing to try anything at this point.

Yes.
Posted via Mobile Device

[67swb72klb]

Originally Posted by 72hoopti

67swb,
you have to run a ground wire from that bottom post to make it work?

I have another 72 and that is not the case. And yes, the temp gauge works in the truck

no the ceramic resistor was bad in my case
good luck

[BruthaMan]

Guys, I've been keeping track of this NOS temp sending unit for the past few days:

http://www.ebay.com/itm/350864999231...84.m1438.l2649

Knowing that this thread may be referenced years down the road, that auction for an NOS temp sending unit started out around $35 when I saved it to my watch list. It's now over $100 for the temp sending unit.

I've seen similar behavior with others. This one is for a camaro, but I believe the only real difference in these temp sending units was the connector style. In fact, this is the same style I ordered from Lectric limited, because my green wire for the sending unit was already setup with a round connector for the small bolt to hold it in place.

Amazing. Just thought I would post this, in case anyone runs across some NOS units out there. There's money to be made on these old sending units!

[72hoopti]

Gauge is dust. Ordered a new one- aftermarket. Anyone put an after market gauge in? If so, any problems to predict?
Posted via Mobile Device

[72hoopti]

Alright guys, talk me off the cliff here. I just threw in my new gauge and nothing. Yes, the gauges moves(a slight bit) but will not get past the first hash mark on the temp gauge!!!!!!
Ay input would be great. I know bruthaman had problems with temp sensor but i would hate to go through hassle when it was an ohm/electrical problem.
Posted via Mobile Device

[BruthaMan]

In a holding pattern to test this on my '78. Did receive the sending unit.

Should have the Edelbrock metering kit in today. Everything else is ready. Just waiting to be fired up.

[Bryan H]

Have you replaced the 2 4amp fuses at both front fenders in the wiring harness? I had 1 blown, replaced it, and my gauge works fine now.
Posted via Mobile Device

[Bryan H]

Mine is a 71 but I think all 67-72's have these. They are short ones in the corners of the front fenders in the wiring harness going across the front of the radiator support.
Posted via Mobile Device

[Bryan H]

Sorry that was for my amp gauge!!!!!!!!!! I guess it was too early in the morning and my brain wasn't working!!!!!!!!!!!

[Sklptrljay]

*Subscribed

[72hoopti]

Does anyone remember what color wire runs to the tem sensor? I have assumed it was a green wire but have no continuity from green wire on sensor to green wire in plug that goes into back of cluster.

HELPPPPPP!!!

[beetle1960]

Green....