Temp Switch/Sender only works at ignition on. Nothing after engine start (Page 1/1) Zeppelin1007 JUN 07, 05:36 PM Hey Guys, Pulling my hair out over this one Have an 86 Fiero, automatic, 2.5 iron duke. Starts up. Drives. Gauge cluster has plenty of issues so I'm trying to start 1 by 1 and solve them. First off - My temp gauge pegged to the right. Ok. Swap the temp sender and switch (one piece) Now it just sits at 100 no matter the temp when the engine is on. So following the test procedure, if I put the key at half turn and just get accessory lights. Unplug the sender unit. Try grounding the one side to the engine. Hey! Overheat light comes on....but no fan...uh. ok. Ground the other wire to the engine and the gauge pegs to the right. Add aa 55ohm resistor, and it goes to around 260. Soon as I start the car though, and try to repeat this procedure, gauge just sits at 100 or less and the overheat light doesn't come on. Should it? Am I missing something? Other clues worth mentioning - blinkers are slow. Oil pressure gauge pegs right when on. Fuel gauge doesnt do anything. Tach and speedo work! I'm guessing I'm hunting for a bad ground somewhere? Possibly ignition switch? Thanks in advance guys. J Gunsett JUN 08, 09:29 AM You can use the 55 ohm resistor to check the oil pressure gauge, should read about 2/3 scale. Remove connector and insert resistor to ground. If you want the Temp/fuel gauge checked out or repaired yet me know. Jack Eliredandblack JUN 08, 09:46 AM The temp gauge that is pegged on start is a common problem from the factory. You will need use Google to find out the steps to correct this and which wires need to “Reversed” on the two large connectors behind the instrument cluster. Instead of trying to remove the wire pin from each connector, I just cut the wire and then soldered it to the other connector. If you don’t have a Factory Service Manual it’s going to be extremely hard to figure out your wiring problems. Good Luck. Zeppelin1007 JUN 08, 02:09 PM Right, Im aware of testing the oil gauge and how to stop the temp gauge from pegging. Trying to get it functional before I do that. Why would the temp gauge and the overheat light stop working once the engine is started? But it works on ignition on?