GMdesigner

Hi All,
Greetings! New member here. I got a wonderful, original, low mileage '61 F-85 (yes, transmission broke but it's fixed now and that's not why I'm here) and I got a rather banal question pertaining to the telltale lights in the instrument cluster. Does anybody know if all three (GEN-TEMP-OIL) are supposed to come on with the ignition turned to "on" or just GEN and OIL? I can't find any reference in either owner's manual or shop manual to whether the TEMP light is intended to go through a check cycle like the other two lights when the ignition is turned on. I tested the TEMP bulb by grounding the connector and it's intact, so that part is fine. On a car that has only an idiot light for a hot engine warning, I want to be absolutely sure the telltale works as intended. My next step would be testing the sensor itself. I'm not keen on destroying the car's 100% originality by adding non-stock gauges, so I want to be as sure as I can be that the TEMP telltale is working reliably. Thanks!
Marc

jaunty75

I think you can pretty safely assume that the TEMP light should light up momentarily when the car is started just like the oil and gen lights do. The purpose of this is to verify that the circuit for each is good and that the bulb works. If your TEMP light doesn't light up and you've verified that the bulb is good, you need to check the wiring between the temperature sending unit and the dashboard. But if it were me, I'd go to the nearest auto parts store and spend $11 and replace the temperature sending unit as I'll bet that's the problem. I wouldn't worry too much about originality. This is a wear part, like fan belts and oil filters, and no one expects a 56 year old car to still have its originals of those, either.

http://www.autozone.com/engine-manag...eVehicle=false

oldcutlass

The temp switch is open unless the coolant temp reaches the point at which it closes and lights the light. I doubt thats the problem. Look at your electrical schematic to see where the indicator lamp gets the ground signal during the self test.

GMdesigner

Thanks, Jaunty75, I did check the wiring by pulling the connector off the sending unit and grounding it and then the telltale works just fine when the ignition is switched to "on" so I know that part is ok. I'm not worried about affecting originality by replacing the sending unit, of course. I merely don't want to have to install a non-stock temp gauge (or any others) and alter the appearance of the instrument panel that way so I want confidence that the idiot light works properly. I was just curious if anybody knew for sure if the set-up was supposed to check the TEMP function as well by lighting all three telltales during routine starting/ignition cycle or just GEN and OIL. There's only one wire to the sending unit, so unless a check-cycle function is built into the sending unit, it would seem that perhaps it wasn't intended for the TEMP light to come on briefly during ignition/starting. As I said, can't find any reference to it in either the owner's or shop manual.

oldcutlass

Looking at the schematic, there is no self test feature for the temp light. There is a yellow power wire on one side of the light and a pink sense wire on the other. Oil pressure and gen lights come on because the oil pressure switch is closed with the engine not running as there is no oil pressure, the gen light is on because there is no voltage on one side.

jensenracing77

I did not read the replies but with the ignition in the on position and the engine off, it will have the generator light and oil light on because they are not charging or pumping oil when the engine is off. I can't say for sure on the 61-63 model years but I believe when you turn the key to the start position then temp light will also light up to test the bulb. I know this is true on newer years. I will have to go out and look at my 62 and see if it has this test.

joe_padavano

Now there's a novel concept...

The early cars do not have the ground wire from the ignition switch that provides the "lamp test" function for the TEMP bulb that later cars have. The GEN and OIL lights are naturally grounded with the engine not running and thus do light up at start.

JohnnyBs68S

Keep in mind, that the "test" feature on the later cars only tests the lamp, not the sender. If you are relying on the sender to tell you if the engine is overheating (YES!), then putting in a new one or testing the old one (removed and put in a frying pan?) is the final check you need to do.