Temp gauge/sensor/wiring ?

[magnethead]

I was driving back from town today and the gauges were normal (45 PSI/1st temp mark/14 volts) and when i looked down after feeling hot air hit my hand out the window, i saw the temp gauge pegged so i shut it down. The upper radiator hose was hot (first thought was thermostat), the overflow was empty, and the gauge hadn't moved when the ignition was turned off.

We just limped it home, and the radiator has full water in it, but i'm not sure about the gauge..where does the wire from the sending unit go on the back of the cluster? Theres 3 metal terminal type things that have ~3/16" holes below and left of the light hole, but they appear to not of had a connector on them based off of previous imagery.

I have the feeling it's electrical because when I pulled the gauge cluster, who knows what may have been accidentally pulled loose (Already found out i yanked the speedo cable out of the connector under the hood, tape fixed that).

[magnethead]

[79BIG10]

Not sure on the wire on the inside behind the cluster but the wire to the temp sending unit in the head is a green wire with a plastic (yellowish) clip on it. The clip just slides onto the sending unit.

[magnethead]

I got the wire (thumb is to the right of the big one), and the connector came off it and who know's where it is. Per prvious photography, not sure it's connected with pulling the dash- I have a picture of the tach installed (post dash removal) and the gauge is still working. Although i'm thinking it probably didn't help. I've grounded the wire and ungrounded it, it stays pegged. I'm going to grab my meter and check continuity of the wire to ground to see if the jacket's been pulled back or something and it's toucing ground.

[jimmmie '79 Cheyenne]

Just recently had the same prob on my '79. After changing the sending unit and t-stat I was able to get my gruby paws on a instrument cluster and swap out the guage. Yea, it worked. Did a little trouble shooting on the guage and found the "shunt" (ceramic piece that bolts on the back of the guage) was bad. I was able to find a new shunt at www.fix-a-gauge.com/faq.php for about $8. If you know the resistance and wattage you can pick up the resistors at Radio Shack for a lot less. The shunt was also bad on my gas gauge and I repalced it along with the oil and volt meter just because. While it was all apart, I painted the back of the black panel with chrome paint and cleaned all the bulbs and sockets. Went one step further and ordered the clear lense from LMC. Now I can read the odometer!!! Hope this helps...

[magnethead]

thanks for the input, hoping it's not the gauge...

I just metered the wire on the 2K/ " ->|- " setting and it registered 0.069 from ground to the wire, with it disconnected (0=full continuity, 1 = no continuity). So I'm thinking that wire has been cut through somewhere and is contacting ground.

[jimmmie '79 Cheyenne]

I didn't measure the resistance to ground with the connector off the sending unit. I did however, disconnect the sending unit, physically move the needle down on the gauge, turn the key on and the gauge pegged. Only thing to cause this would be the wire or the gauge - good luck... Guess you could pull the gauge out and check the resistance to ground on the "sender line" should be open.

[magnethead]

where did the wire go on yours? I found 2 wires on that main wire harness thing but aint sure how it comes off or if wither of them are even the right one...

[jimmmie '79 Cheyenne]

Got flustered and didn't have enough patience or refreshment to trace the wire from the sending unit - think it was green. That's when I swapped the gauge.

[magnethead]

i know it's green..the thing is, i know one end is shorted out to ground, i need to find the other end, wether it be in the big harness or a single wire floating around.

[magnethead]

think i figured it out.... can't explain the DMM reading, but i just moved my truck with the wire ungrounded and gauge went to vcold...so i guess that's all it is, the ign needs to be turn on to reset the gauge.

[magnethead]

fixed...for now

got a speaker spade connector on it till i can get back to orielly's and buy the proper connector.