74 C10 Temp Gauge

[Bandit130]

Gauge stopped working intermittently. Lately, sometimes when key to ON, hand would move from below C to first mark on gauge then would drop to below C when started. Next, it would go from below C to first mark when key to ON, would drop below C in about 2 seconds without starting engine. Then did not work. Have replaced gauge with new one and same situation. Does anyone have any ideas? Most of the time now hand does not move at all.

Replaced temp sending unit and connector (nail head) last fall. This problem started within the last month. Before that worked fine.

TIA

[sdewolfe]

You have replaced the sender and the gauge. Assuming the wiring and gauge cluster are original, the only component left is the ignition switch. That doesn't seem likely because you did not mention the fuel gauge and it relies on switched power too. I reckon you have checked the green wire for continuity from the connector to the sender. Too, you have already replaced the gauge so you had access to the printed circuit and clips. You would have corrected any problem there. Remove the wire from the sending unit and ground it. Turn the ignition ON. The gauge should peg full HOT. If it does not, the sender is eliminated as a suspect. It is possible but not probable that two gauges could exhibit the same symptoms. So...

Disconnect the battery.

Clean the harness connector pins. Pull the connector from the back of the cluster. You may need to untie the run from the main harness to get enough access to the connector. I found it easier just to remove the cluster, which I had to rebuild anyway. You do not need to push the pins from the connector unless you just want to do so. Get four containers large enough to receive the entire connector. Large SOLO cups work for this. Put a 50/50 mix of vinegar and water in a cup and submerge the connector. Leave it for about two minutes. The pins will be bright and shiny when you pull it out of the vinegar. Now dip the connector in another cup with 1 Tbsp. of baking soda fully dissolved in plain tap water. Dip it and swirl it around to neutralize the vinegar. Rinse in a cup of plain water. Finally, dip the connector in a cup containing rubbing alcohol, again dipping and swirling, to absorb the water. Let it air dry. Now is the time to treat the pins with contact grease. (CRC makes a small tube which is available at most auto parts stores for less than $5.) I pushed some grease into the connector from the backside too. But then, I am a belt and suspenders kind of guy.

Reconnect everything. The gauge should work.

Why do I suspect tarnished pins? Because it started acting strange before it quit altogether. There is either a broken wire, which I assume was checked, or a high impedance connection, which cleaning will remedy. Going back to the gauge, if the clips there are tarnished, you could have the same symptoms. If in doubt, clean them the same way you cleaned the connector. Replace any damaged clips (and even the printed circuit if it is damaged at all). I cleaned the posts on the gauges too. I do not suspect a lifted ground because the temp gauge is the only one you mentioned as malfunctioning. If other gauges are involved, they all need a good ground.

I just noticed that you replaced the connector when you replaced the sender. Did you splice it to the wire or use a new pin and housing? If spliced, check that.

[Bandit130]

SDEWOLF...

You posted (Remove the wire from the sending unit and ground it. Turn the ignition ON. The gauge should peg full HOT. If it does not, the sender is eliminated as a suspect).

The gauge did peg hot when connector from sender was grounded with ignition switch on. Does this mean the sender is defective? Still in process of testing pins and wiring.

TIA

[Honest Bob]

Subscribed!

I think I have a similar issue. Mine only works if the key is in the off or on position. If the truck is running it wont work (although I did catch it working once).

[Bandit130]

After exhausting all gauge testing I could, decided to replace sender. Fixed issue even though I had replaced it last fall. Now gauge hand stays at 12:00 without AC and 1:00 position using AC. Shocked it was just sender.

[Jstock85]

Glad it was a simple fix! I usually have to tear half the dash out when my gauges go berserk!!