temp light

[lgehring]

1966 c20 with idiot lights, should the red light come on when you turn the key on or just when the engine is too hot? The green one works as it should. Thanks Lowell

[Mike Wessinger]

Bumping this up. I have the same question and have not found my answer yet in searching. Mine does not come on when I turn on the ignition, and currently my green does not come on at all. I have replaced the bulbs and no change, so looking for some info.

[1963c-10]

Its been some time since I had warning lights, but I remember them both coming on and only a green light while the engine is cold.

Mike.....Id replace you temp sending unit since you've already replaced the bulbs. Also make sure the wire is connected to the sender. Its possible that someone unplugged it at some point.

[Mike Wessinger]

Originally Posted by 1963c-10

Mike.....Id replace you temp sending unit since you've already replaced the bulbs. Also make sure the wire is connected to the sender. Its possible that someone unplugged it at some point.

Thanks for the follow up. I found another discussion about grounding the contacts at the sender to check the circuit. One bulb was DOA, but swapping the good bulb and grounding each terminal at the sender lights up in both sockets. The green light is not coming on with a cold start though. I have a new sending unit on the way so I have a Saturday project. Thanks again for the help.

[1963c-10]

no problem. the sending unit is an easy fix...takes 2-3min

[ncoonen]

You might want to check out THIS thread for a complete tutorial on the temp light circuits. I suspect that many a sender has been swapped out for want of a good electrical connection somewhere along the way.

Sounds like you have got your problem solved and I know that's a good feeling.

...ned.

[Mike Wessinger]

Originally Posted by ncoonen

You might want to check out THIS thread for a complete tutorial on the temp light circuits.

Thanks for the link. Great info.

With the connector partially plugged onto the temp sensor, if I clip my test lead to ground each blade, the lights will come on. So it looks like the connections inside the plug are good too, just need the new sensor now.

[Wrenchbender Ret]

The red light should come on when the key is turned to start position. The green comes on when the key is in run position & goes out when the coolant starts to warm up. Its a good idea to replace the sending unit everytime you get a truck with this system. There is no easy way to test the hot side.

[cg285]

Originally Posted by Wrenchbender Ret

The red light should come on when the key is turned to start position. The green comes on when the key is in run position & goes out when the coolant starts to warm up. Its a good idea to replace the sending unit everytime you get a truck with this system. There is no easy way to test the hot side.

my engine starts so fast i don't have time to see if the red light comes on. what could be my problem?

[ncoonen]

Originally Posted by cg285

my engine starts so fast i don't have time to see if the red light comes on. what could be my problem?

I'll answer assuming your question isn't sarcastic. Turn the ignition key to RUN and the green light should be on. Slowly turn the key toward START and the red light should come on before the starter solenoid gets power and engages. Now I understand that all fifty year old ignition switches might not work that way but that is how it should work.

So, to answer your question directly, your problem might be too much coffee.

...ned.

[cg285]

hahahaha

[Old Bleu]

This thread got my attention because neither my hot nor cold light has ever worked in my '64 truck. I installed a new sender unit when I replaced my water pump because I noticed that one of the blades on the old sender unit was broken off. But still have never got the lights to come on even though I have tested both lamps, and they are good.

Based on what I read here, I pulled the L-shaped connector out a bit (but still connected to the sender) and attached a ground wire to one terminal and I had a Cold light for the first time! I then moved it to the other termindal and the Hot light was lit. I also used my test probe from the positive battery terminal to the brass body af the sender unit, and it lit. So I assume that my sender is grounded (was afraid I might have used too much tread sealant).

But I still have no lights if I don't ground the terminals... So I guess I don't understand where my problem lies... Is my L-shaped connector bad? I tried scraping the female connections with a small screwdriver and reconnecting it, but that did nothing. I assume the connections are good because both lights work when I ground each terminal.

Any help would sure be appreciated. It would seem that I am close, but no cigar. :-)

[cg285]

ohm out the cold side - terminal to ground. if no continuity then sender is either bad or the wrong one

[aerotruk63]

[Old Bleu]

Thanks for the test procedure cg285. It looks like I have a bad sender unit. I was beginning to suspect that yesterday after I found that the lights did work when grounded. I bought this unit from Classic Parts along with the rest of the colling system parts, but guess that I got a bad one. My local NAPA store will have one for me today by 2:00 though.

[Old Bleu]

Put the new temp sender in without losing a drop of coolant (drained a gallon out of the radiator to lower the water level) and immediately had a Cold light when I turn the key on. That's a first since I've had the truck! I'm sure I'll see the Hot light come on when I crank it, but letting the tread sealant harden before refilling and cranking it. Thanks to this thread, I now understand how this thing works!

[1963c-10]

Glad you got it working!!!

[Old Bleu]

I am too! After new brakes, the first thing I did was rebuild the cooling system, but never knew that my new send wa bad right out of the box. But I guess better that than hacked up wiring.

[Mike Wessinger]

Sounds great. I am hoping FedEx is not too late showing up at my house tomorrow so I can get mine installed. The truck was originally my grandfather's, and I have had it for the past 13 years. In the time I have owned it the cold light has never functioned properly.

[Old Bleu]

Having your grandfather's truck must be great Mike! I hope your sender comes in time to install it. A 15/16" socket or wrench and some thread sealant ought to be all you need. I drained a gallon from the radiator, and didn't see a drop of water when I removed the sending unit.

Let us know how it goes. My cold light came on and stayed on until the truck warmed up, then it flickered out. I don't think I saw the hot light though when I cranked it though. I'll be curious to know if you do.

[Sharps40]

Originally Posted by Old Bleu

Having your grandfather's truck must be great Mike! I hope your sender comes in time to install it. A 15/16" socket or wrench and some thread sealant ought to be all you need. I drained a gallon from the radiator, and didn't see a drop of water when I removed the sending unit.

Let us know how it goes. My cold light came on and stayed on until the truck warmed up, then it flickered out. I don't think I saw the hot light though when I cranked it though. I'll be curious to know if you do.

Based on responses I got to the same question last month, the service page above and my own experience....Normal function is: green light when ignition is turned on and stays green till its warmed up. No red light at all till it overheats.

[jayoldschool]

Anyone have a source for the sender? Mine's melted where the harness plugs in.

[jtrichard]

Originally Posted by jayoldschool

Anyone have a source for the sender? Mine's melted where the harness plugs in.

http://www.napaonline.com/Catalog/Ca...625_0275719146 63 to 66 $18

[jtrichard]

Originally Posted by lgehring

1966 c20 with idiot lights, should the red light come on when you turn the key on or just when the engine is too hot? The green one works as it should. Thanks Lowell

YES the "red/hot" light is supposed to light up when you crank the engine over ...there is a dark green wire on the back of the ignition switch... if you can ground that wire (with out pulling it off of the switch and the key in the run position) it should light up if it does BUT NOT when cranking then you have a bad switch

[jtrichard]

should not be hard to find that plug/connecter as it was used in 163 different GM and Dodge models from 62 to 70