Temperature Sending gauge question

[fumehappy]

Hello, trying to troubleshoot a problem. My temp gauge keeps pegging to the right, or infinite hot. I took the lead of the sending unit on the head, and there was no change. Taking a multimeter and placing it on the sending unit with the read lead (black to chasis ground) i got 1.410.. and it started marching downward which is expected. So I pulled the instrument cluster cover. If i take the temp gauge out, there are three clip contacts on the pastic backboard, 9, 12, 3 o'clock. 9 o'clock appears to be the sending unit, as it the resistance corresponds to the unit in the head. 12 appears to be the ground, and 3 appears to be the hot-leg.( reads 14 ish volts) I took the resistance reading using the ground contact, so I know that's good. My temperature gauge itself has four screws on the back at 12, 3, 6, and 9 oclock. Does anyone if there is a resistance I should look for in testing it across the contacts?
Thanks!

 

[HotRodPC]

Don't get to carried away just yet. Start with simple. 9 of 10 times, when infinite or full hot, your green wire from the sending unit is grounding out, likely on an exhaust manifold. Sometimes grounding on the firewall too where the grommet might have gone bad. Check that wire, then the next thing I'd suspect for going intermittent infinite is the gauge sender itself.

 

[chengny]

X 2:

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[fumehappy]

Thanks for the diagram! I used a different ultiimeter and got measurements from the clips that lined up with it. I also got 85 ohms across the ceramic resister on the back of the gauge itself. I used a steel brush in the dremel and cleaned all contacts on the gauge, then pinched the clips in the cluster closed a bit. I am happy to report all is working well now!

 

[HotRodPC]

Great, Thanks for the update. Most newbs don't report back. Popped your cherry and gave Rep.

 

[fumehappy]

Just wanted to post some additional info. After initially working okay, the gauge went back to infinite hot again. I pulled the Instrument cluster, cleaned and re-bent all the clips(so they didn't jiggle on the circuit). Cleaned the ground contact and the circuit board harness contacts too. After that I got a solid ohm reading from the 9 o'clock position (i verified with the circuit on back, the above diagram did no apply to my truck).
I then tried to check the resistance of the ceramic resistor on the back of the gauge. I got "1" meaning no circuit. Come to find out there was a break in the conductivity of the resistor, and after a little "engineering" I got contact to the terminals, and confirmed an 86-89 ohm reading across. Been working fine for two days now, but I have a new 90 ohm resistor on order.

 

[HotRodPC]

Just wanted to post some additional info. After initially working okay, the gauge went back to infinite hot again. I pulled the Instrument cluster, cleaned and re-bent all the clips(so they didn't jiggle on the circuit). Cleaned the ground contact and the circuit board harness contacts too. After that I got a solid ohm reading from the 9 o'clock position (i verified with the circuit on back, the above diagram did no apply to my truck).
I then tried to check the resistance of the ceramic resistor on the back of the gauge. I got "1" meaning no circuit. Come to find out there was a break in the conductivity of the resistor, and after a little "engineering" I got contact to the terminals, and confirmed an 86-89 ohm reading across. Been working fine for two days now, but I have a new 90 ohm resistor on order.

So you're saying the guage itself went bad and you're repairing it??? That's the kinda **** we like here. We don't like parts changers much.

I'll add, actually we're good with swapping a gauge. We don't like the guys that just replace part after part trying to guess at a problem. We prefer to diagnose it, even if it takes all our heads, find out what the issue is, then make the repair.

 

[S.R.R.]

Can these factory resisors be ordered? I swapped some out from one gauge cluster to another one. Also wondering if someone has a chart that shows what the different colors of then mean. Thanks.

 

[highdesertrange]

x2 on proper troubleshooting and not just replacing parts willy nilly. highdesertranger

 

[HotRodPC]

Can these factory resisors be ordered? I swapped some out from one gauge cluster to another one. Also wondering if someone has a chart that shows what the different colors of then mean. Thanks.

Resistor to what? As far as factory resistor... A resistor is a resistor. Doesn't have to be a GM Factory resistor. I'm certain google would be a good source for a resistor color band chart.

Last time I needed a resistor when a $225 circuit board to my rent house Heat and Air went bad, and was going to be a week before it came in on order from FL. I pulled the board, seen the obvious burnt resistor. Took the board to Radio Shack, matched the color bands and bought a 5 pack of resistors for like $2.49 if I remember right. I heated the solder, pulled the old resistor out, slid the new in before the solder cooled and done. Installed the board and Heat and Air worked perfect and was still working 2 years later when I lost the house to divorce. Saved over $220 for the board + $125 service call/labor and my tenants didn't have to go over a week without heat.

 

[GTME94]

There is a saying I learned when taking an Electrical Engineering class to help remember the color to number sequence.

Black Buicks Run On Yellow Gas But Volkswagens Get Wound.

Black =0
Brown = 1
Red = 2
Orange = 3
Yellow = 4
Green = 5
Blue = 6
Violet = 7
Grey = 8
White = 9

Silver = 10% variability
Gold = 5% variability

I took that class 20 years ago and am not an electrical engineer or do any electronics work but somehow remember it since it is such a unique saying.

Or more easily just Google it and it will give you a picture.

 

[74 Shortbed]

Never heard of that before, pretty cool..