Temperture gauge is pegged on high

[dmjlambert]

Originally Posted by Seventy Two

Hey LockDoc, I have a photo but not sure how to load it. I think I need a photo bucket or something. Is there tutorial on this forum that will explain how I do this?

To post pictures, click the Go Advanced button if you see one below where you are typing your reply. Then scroll down and click the Manage Attachments button. A dialog will pop up that you can use to upload pictures.

[LockDoc]

Originally Posted by Seventy Two

Hey LockDoc, I have a photo but not sure how to load it. I think I need a photo bucket or something. Is there tutorial on this forum that will explain how I do this?

Sent you a PM.

LockDoc

[Seventy Two]

This is my attempt to add the photo of the back of the temp gauge.

[LockDoc]

Originally Posted by Seventy Two

This is my attempt to add the photo of the back of the temp gauge.

Good job! I flipped it for you. Everything looks good there.

LockDoc

[Seventy Two]

Thanks Lockdoc, I appreciate your help.
Posted via Mobile Device

[tdangle]

Originally Posted by gmc684x4

Removing the wire from the sender will not make the guage start reading cold as the circuit is incomplete and will need to read 300 plus ohms to drop its reading
That it re pined reading after you zeroed out tells me that 20Dg wire is shorted to ground somewhere

I believe you are wrong here. I have removed the wire to the sending unit and it reads dead cold. The meter works with +12v from the ignition to the gauge and the other side of the gauge goes to the sending unit. As resistance lowers it reads higher. Basically it is a simple volt meter calibrated to show temperature.

[tdangle]

Originally Posted by Seventy Two

tdangle, With the sending wire off and key on it still reads hot and this is with a new sending unit from Napa.

Then you have a short in the wiring from the sending unit to the gauge cluster that is shorting to ground. Unplug the connector at the back of the gauge cluster and use an ohm meter 1 lead to the wire 1 to ground. You will see continuity and shouldn't as now this is just a wire hanging in the breeze. If you don't see a. short in the wire to ground, then you have a short in the gauge cluster. Troubleshooting is best done with a divide and conquer method.

[VetteVet]

Originally Posted by tdangle

Then you have a short in the wiring from the sending unit to the gauge cluster that is shorting to ground. Unplug the connector at the back of the gauge cluster and use an ohm meter 1 lead to the wire 1 to ground. You will see continuity and shouldn't as now this is just a wire hanging in the breeze. If you don't see a. short in the wire to ground, then you have a short in the gauge cluster. Troubleshooting is best done with a divide and conquer method.

This is very good advice and I might add that the gauge itself on the sender side, is insulated from the metal mounting by a small piece of tubing, this might be your short to ground. Unplug the dash plug and read the DG wire as suggested for resistance to ground, between the sender end and the wire at no.6 on the dash plug for zero ohms to ground, and then read the ends of the wire for zero ohms, just in case the wire is cut or open at some point between the two ends.

[Seventy Two]

Divide and conquer! I like it and its working. I pulled the lead from the sending unit and connected to the ohm meter with the other lead to ground. No continuity! Nice right.
As per Vettvet I checked for continuity between the sending unit end of the lead and the #6 wire at the cluster plug in. Full continuity, "beeP" This is good, right? So it may be that I have short at the cluster itself. Im not sure what Vettvet means about a small piece of tubing for insulation. Post # 53 is my cluster and I dont have piece of insultated tubing that I recall. Can some provide more detail (perhaps a picture) of this?

[dmjlambert]

I have a suggestion. Disconnect the neg post of the battery. Connect the instrument cluster connector to the instrument cluster. Remove this nut and remove the printed circuit from the lug.


Grab the copper pad of the printed circuit with an alligator clip test wire. Use some tape if necessary to keep that part of the printed circuit or the alligator clip from touching the lug of the gauge.

Test 1

Disconnect the sender wire from the sender. Now test continuity all the way from the sender wire to the printed circuit end that you have the alligator test wire attached to (should have continuity). Disconnect one of the 2 ends from the continuity tester and test for continuity to ground (shouldn't have continuity).

I favor using the ohm setting and actually measure the number of ohms instead of (or in addition to) relying on a continuity test beep. Use the lowest range on the meter (perhaps 200 ohm range, meters vary). There should be few ohms, perhaps less than 20, along that wire. Use the large range on the ohm meter (perhaps 2000K, meters vary) to test for short to ground. You should get no reading.

Disconnect ohm meter and reconnect the neg post of the battery.

Test 2

With that flap of printed circuit still disconnected from the gauge post, turn the key to on. Is the gauge still pegged on hot? If so, I'm thinking there is something wrong with the gauge or something wrong with gauge installation.

Disconnect the neg post of the battery, reconnect flap of printed circuit to the gauge, and connect terminal to sender, then reconnect neg post of battery.

[tdangle]

Originally Posted by Seventy Two

Divide and conquer! I like it and its working. I pulled the lead from the sending unit and connected to the ohm meter with the other lead to ground. No continuity! Nice right.
As per Vettvet I checked for continuity between the sending unit end of the lead and the #6 wire at the cluster plug in. Full continuity, "beeP" This is good, right? So it may be that I have short at the cluster itself. Im not sure what Vettvet means about a small piece of tubing for insulation. Post # 53 is my cluster and I dont have piece of insultated tubing that I recall. Can some provide more detail (perhaps a picture) of this?

Your getting there. Good that you have continuity for the wire from the sender to the gauge cluster connector. Did you also verify that that wire is not shorting to ground? Always try to think logical and keep it simple.

[Seventy Two]

I will let you know how it goes. Thanks for the suggestions.

[Seventy Two]

Originally Posted by tdangle

Did you also verify that that wire is not shorting to ground? Always try to think logical and keep it simple.

No I guess I didnt. Do you mean checking the #6 end of the wire from shorting to ground?

[Seventy Two]

Test 1

Disconnect the sender wire from the sender. Now test continuity all the way from the sender wire to the printed circuit end that you have the alligator test wire attached to (should have continuity). Disconnect one of the 2 ends from the continuity tester and test for continuity to ground (shouldn't have continuity).

I favor using the ohm setting and actually measure the number of ohms instead of (or in addition to) relying on a continuity test beep. Use the lowest range on the meter (perhaps 200 ohm range, meters vary). There should be few ohms, perhaps less than 20, along that wire. Use the large range on the ohm meter (perhaps 2000K, meters vary) to test for short to ground. You should get no reading.

Test #1 complete and the results were consistent with your view. Ohm reading from the end of the sender wire to the circuit board was 1.3 ohms.
Then grounded the sender end - no continuity was the result.
On to test #2.

[Seventy Two]

Originally Posted by dmjlambert

Test 2

With that flap of printed circuit still disconnected from the gauge post, turn the key to on. Is the gauge still pegged on hot? If so, I'm thinking there is something wrong with the gauge or something wrong with gauge installation.

Disconnect the neg post of the battery, reconnect flap of printed circuit to the gauge, and connect terminal to sender, then reconnect neg post of battery.

Unfortunately, yes the gauge is still pegged on hot after conducting test number 2. I tried it with the sender wire connected to the sender and disconnected just to be sure. Look another WALL.

[dmjlambert]

How many ohms do you measure between the top and bottom pins of the gauge? That blue thing is a resistor.

[Seventy Two]

Originally Posted by dmjlambert

How many ohms do you measure between the top and bottom pins of the gauge? That blue thing is a resistor.

I get 130.1 ohms between the top and bottom on the resistor.

Post to post (+/-) 46.7
low end resistor to ground 0.7
upper end of resistor to ground 130.5
left post to ground (viewing from the front of gauge) 66.1 ohms
right post to ground 103.3

Thoughts?

[Seventy Two]

Just to clarify, I meant 130.1 ohms on the resistor "posts"

[dmjlambert]

Well I get 38 ohms between top and bottom resistor posts. Perhaps you have a bad resistor. According to that post #4 67swb72klb gave, it should be a 90 ohm resistor. I suppose it reads less when it is in the circuit because it interacts with other components. Perhaps you could unscrew those nuts and remove the resistor and measure the resistance of it when uninstalled.

[VetteVet]

The terminal that Mr DJLambert has pointed to in post 60 is the no.6 wire sending unit terminal. With your dash plug pulled, test for ohms between this terminal and ground if you haven't already. If you get a very low reading your gauge is shorted to ground. Or the circuit wire to the gauge is shorted to the dash which is grounded. I would disconnect the circuit board terminals and test the terminals and the board wires to ground. The right hand wire is the power wire for the temp gauge from the fuel gauge and the no. 3 terminal on the dash plug so it wont be shorted to ground. If you get a very low reading on the sender side terminal, remove the small nut and washer under the nut and you can see the small tube that insulates the gauge terminal from the dash.

[Seventy Two]

Originally Posted by dmjlambert

Well I get 38 ohms between top and bottom resistor posts. Perhaps you have a bad resistor. According to that post #4 67swb72klb gave, it should be a 90 ohm resistor. I suppose it reads less when it is in the circuit because it interacts with other components. Perhaps you could unscrew those nuts and remove the resistor and measure the resistance of it when uninstalled.

Well the results are in! Trying measure the ohms on just the resistor, I got nothing at all.

[Seventy Two]

Originally Posted by VetteVet

The terminal that Mr DJLambert has pointed to in post 60 is the no.6 wire sending unit terminal. With your dash plug pulled, test for ohms between this terminal and ground if you haven't already. If you get a very low reading your gauge is shorted to ground.

I measured this terminal to ground and got 195.2 ohms. If you think this is low, I can try removing the board from the terminals and measure the two posts and the two board contacts to ground and see what I get.

[Seventy Two]

Question Vettvet, when I test the terminals and board contacts to ground, do I have the dash plug back in?

[dmjlambert]

Originally Posted by Seventy Two

Well the results are in! Trying measure the ohms on just the resistor, I got nothing at all.

Mine from a working gauge reads 75 ohms. It looks different than yours. Mine looks like thin wire wrapped around cardboard.


You may be able to get one by PM to TBONE1964, he specializes in working on instrument clusters.

[VetteVet]

Originally Posted by Seventy Two

Question Vettvet, when I test the terminals and board contacts to ground, do I have the dash plug back in?

No you've already tested the no.6 wire so no need, you want to test just the gauge and the circuit board.