Tempture gauge isn't working - The 1947 - Present Chevrolet & GMC Truck Message Board Network

putnam00 · 09-11-2012, 11:27 PM

I'm having a problem. I got rid of the dummy lights on my 71 c-10 and a gauge cluster from a 72 GMC, I rewired the harness for the gauges. I am running an lt1 and had to use a sending unit that has smaller threads for the heads. what I was told is the resistance is the same on the sending units. when I turn on the key on it went strait to Hot. I had to ground the gauge to get it to go to Cold but my engine fan turns on at 210 and with it ungrounded it is always hot and grounded always cold. my other question is what is the resistor on the ground for? Please help

davepl · 09-11-2012, 11:33 PM

Did you get the appropriate sender for the gauge? The idiot light ones are off/on, the gauge ones are variable. And somewhere in the 70s or 80s they changed the resistance curve, so double-check that the resistance is, in fact, the same as what your gauge wants (as opposed to whatever the guy who sold it to you hopes it is).

If you used teflon tape or a brass bushing, you might have insulated the ground path, though I'd think that would make it show cold, not hot.

What resistor on the ground? Did you drop one? :-)

GuyO · 09-12-2012, 12:11 AM

I think Dave PL is right. I had similar problems - first thing I did was replace the sender to no avail. Then I started at the farthest away from the cluster and removed any teflon, then I found that the green wire had a bare spot for a possible short. Also, I moved the sender to the head and not the intake (not Lt1), finally I sent a private message to VetteVet and he recommended I add a ground from the cluster to the dash. Everything works now.

**special-K** · 09-12-2012, 05:05 AM

When the gauge pegs it means it's grounded.

putnam00 · 09-12-2012, 08:45 AM

I had a wire to the ground on the gauge and That's the only way I can get it to say cold I disconnect that ground and it stays at hot. And when that ground is on and at cold I grounded the sender wire and it went back to hot in ground it and back to cold so it must be my sender. Does anyone know the ohms of the origonial sender? I can't run the orig one because the thread hole is smaller in 89 and up then 1970's
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09-11-2012, 11:27 PM	#1
putnam00 Registered User Join Date: Aug 2012 Location: Grant NE Posts: 78	Tempture gauge isn't working I'm having a problem. I got rid of the dummy lights on my 71 c-10 and a gauge cluster from a 72 GMC, I rewired the harness for the gauges. I am running an lt1 and had to use a sending unit that has smaller threads for the heads. what I was told is the resistance is the same on the sending units. when I turn on the key on it went strait to Hot. I had to ground the gauge to get it to go to Cold but my engine fan turns on at 210 and with it ungrounded it is always hot and grounded always cold. my other question is what is the resistor on the ground for? Please help

09-11-2012, 11:33 PM	#2
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: Tempture gauge isn't working Did you get the appropriate sender for the gauge? The idiot light ones are off/on, the gauge ones are variable. And somewhere in the 70s or 80s they changed the resistance curve, so double-check that the resistance is, in fact, the same as what your gauge wants (as opposed to whatever the guy who sold it to you hopes it is). If you used teflon tape or a brass bushing, you might have insulated the ground path, though I'd think that would make it show cold, not hot. What resistor on the ground? Did you drop one? :-) __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

09-12-2012, 12:11 AM	#3
GuyO Registered User Join Date: Nov 2011 Location: Kirkland, WA Posts: 343	Re: Tempture gauge isn't working I think Dave PL is right. I had similar problems - first thing I did was replace the sender to no avail. Then I started at the farthest away from the cluster and removed any teflon, then I found that the green wire had a bare spot for a possible short. Also, I moved the sender to the head and not the intake (not Lt1), finally I sent a private message to VetteVet and he recommended I add a ground from the cluster to the dash. Everything works now.

09-12-2012, 05:05 AM	#4
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,861	Re: Tempture gauge isn't working When the gauge pegs it means it's grounded. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

09-12-2012, 08:45 AM	#5
putnam00 Registered User Join Date: Aug 2012 Location: Grant NE Posts: 78	Re: Tempture gauge isn't working I had a wire to the ground on the gauge and That's the only way I can get it to say cold I disconnect that ground and it stays at hot. And when that ground is on and at cold I grounded the sender wire and it went back to hot in ground it and back to cold so it must be my sender. Does anyone know the ohms of the origonial sender? I can't run the orig one because the thread hole is smaller in 89 and up then 1970's Posted via Mobile Device



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