Temperature Gauge Issue

[sonicbluezx3]

I just replaced the sensor but still have the problem. The gauge doesnt move at all, so im going to get a new one coming. Im pretty sure that'll fix the problem. I did try to replace the needle too... So i might have screwed somethig up while doing that.

[Tx_Phil]

I'm not an electrical wizard by any means but it seems that you should be able to test this with a digital volt meter before you burn up another gauge.  If you have a grounding short in the wire all you're going to do is roast another gauge even with a new sensor.  Since the sensor sends variable voltage based on resistance related to heat it seems that with a cold engine your volt meter would read a very low voltage when connected in place of the gauge. As the engine temp increases the volt meter should read an increase in voltage.  If you connect the volt meter and turn on the key with a cold engine but read a high voltage then that should point to a short in the wiring which would explain what you are roasting your gauges.

I'm sure there's a lot of folks on here that know this stuff way better then me.  It just seems that a little testing might save you buying more gauges.

[sonicbluezx3]

Good point... I'll have to try that. Although I'm not sure how my wiring would have gotten shorted since I swapped the two gauges over prior to doing anything. I could probably even test this out with alligator clips and the gauge in hand. If the old gauge works with the clips then I'll know it's wiring... if it does the same thing, I'll know it is the gauge. Either way I hope this gets resolved this weekend because I'm ready to drive my truck! Ha.

[sonicbluezx3]

Alright I have done some more testing and I still haven't solved the issue. New gauge (and about 3 diff ones from the junk yard), and replaced the sensor twice (thought the first may have been a defect), and nothing. So here's what I did:
I took the gauge out of the cluster and used alligator clips to connect the terminals on the back to the corresponding things (+ to battery, - to chassis ground, and connected the sensor to the gauge in the right spot... the new one had everything labeled as to where it was supposed to go). It still does not move. So I'm pretty baffled and so is everyone else I've asked. The gauge is new, the sensor is new, and the wiring matches up.
The only thing I can think of is that the wire that connects the ignition switch to the sensor wire (it T's in) sends some sort of signal.

Anyone know? If I can't figure it out I'm probably just going to buy some aftermarket gauges and use those in place of the stock stuff. I would rather get this one working though.

[bd]

Do you have an ohmmeter?

[sonicbluezx3]

Yes

[bd]

Testing the sending unit:

With the engine cold:
Disconnect the wire harness from the sender.  Zero your ohmmeter (if necessary).  Connect one lead of your ohmmeter to the sender terminal.  Connect the second lead of your ohmmeter to a good clean ground.  Measure the resistance and record the reading along with the approximate temperature of the engine.

With the engine at operating temperature:
Zero your ohmmeter (if necessary).  Connect one lead of your ohmmeter to the sender terminal.  Connect the second lead of your ohmmeter to a good clean ground.  Measure the resistance and record the reading along with the approximate temperature of the engine.

Sending unit measurements should range from greater than 1400 ohms cold, up to ~100 ohms at operating temperature.


Making a substitute "test" sending unit:

Pick up a 5,000 ohm (5K) linear taper potentiometer (#271-1714), a 2,200 ohm (2.2K) 1/2 watt resistor (#271-1121), and a couple of alligator clips from your local Radio Shack.  Also, pick up some flexible 18-gauge wire to use for test leads.

Connect the 2.2K resistor across the two outside terminals of the potentiometer.  Jumper the center terminal of the potentiometer to one of the outside terminals.  Connect a couple of 2' long 18-gauge wires to the two outside terminals of the potentiometer.  Connect an alligator clip to the free end of each lead and solder all the connections.


Testing the gauge calibration and wiring:

Zero your ohmmeter.  With your ohmmeter connected to the leads of the potentiometer (pot), adjust the pot to 1365 ohms.  Without changing the setting, attach one lead of your pot to the signal wire from the gauge.  Attach the second lead of your pot to a good clean ground.  Turn the ignition ON and observe the gauge.  The needle should align with the first (left) line of the gauge.

Disconnect the pot from the vehicle.  With your ohmmeter connected to the leads of the potentiometer (pot), adjust the pot to 96 ohms.  Without changing the setting, attach one lead of your pot to the signal wire from the gauge.  Attach the second lead of your pot to a good clean ground.  Turn the ignition ON and observe the gauge.  The needle should align with the center line of the gauge.

Disconnect the pot from the vehicle.  With your ohmmeter connected to the leads of the potentiometer (pot), adjust the pot to 55 ohms.  Without changing the setting, attach one lead of your pot to the signal wire from the gauge.  Attach the second lead of your pot to a good clean ground.  Turn the ignition ON and observe the gauge.  The needle should align with the last (right) line of the gauge.

Edit:
If the gauge needle aligns with the left, middle and right gauge markings as indicated above, the gauge and gauge wiring are functioning properly - look to the sending unit or its ground connection.  If the gauge does not respond as indicated, you'll need to follow up with systematic voltage tests.