If my truck has a temp gauge does the temp light function?

[Rich69shortfleet]

My truck has a factory temperature gauge. I have converted all my dash lights to LEDs. LEDs only work in one orientation so you need to test each light to make sure the bulb is in in the correct orientation. To test the brake warning light I shorted the wire at the brake valve to ground and the dash brake light illuminated. Since my truck has a temp gauge I don't know if the TEMP warning light is even connected to anything. If so, where is it connected? I tried grounding the temp sending unit wire and the light didn't illuminate so I'm guessing it either isn't used or is controlled in some other way.

Also, the TEMP light does not illuminate when cranking which is usually when it is tested with a working light so again, I'm not sure it is even used on a truck with a gauge.

[demian5]

If it does, it should come on when the ignition is on and engine is off.

[davepl]

There's only one sender so unless the gauge clusters have a magic circuit that kicks the light on when the resistance in the sender wire drops below a threshold, it can't.

Since I'm pretty sure there is no second sender or magical circuit, I don't think the temp light functions at all on gauge dashes.

In fact I bet if you look at a gauge PCB vs a standard PCB it'll be obviously not connected, but that's a bet, not a fact.

[StingRay]

Not normally but you can add in a wire and sender in the other head and make it work. Better add a tee to the oil pressure sender line and add an electric idiot light sender and and hook the wire to the same temp light connection and you will have a generic check engine light that indicates one of the gauges may be reading high so time to look! I did this with my 72 and it worked great. The best of both.

[Rich69shortfleet]

It does not come on with the key on and the engine off.

I'll just leave a regular bulb in this one then since it would appear that this light never functions with a gauge set up.

[67chevemall]

Working on switching from after market gauge to factory light. It is a 20g dark green wire if that helps

Defenitly one sensor per option.
Good idea on the 2nd sensor.

[Rich69shortfleet]

Yes, the second sensor idea is a good one. A gauge is great but a light will get your attention better if pressure drops too low.

[Steeveedee]

Just a small correction- the temp light, if equipped, illuminates when the starter is engaged.

[VetteVet]

If you guys have read my posts on this subject I have explained how the light and gauge are wired. Here is a diagram that shows the circuit board and how the light and gauge wiring is connected.





Notice the dashed red line on the left that was connected to pin five on the light dash. The green wire that was connected there was moved to pin 6 for the gauge dashes, and nothing is connected there. It's one of the changes that has to be made when changing dashes.

It's already been said that the key grounds one side of the light when the key is turned to start. This is to test the light. It does the same thing to the brake warning light on both types of dashes.

I've got two gauge clusters and I'll have to check to see if the temp light came installed with them.

[Rich69shortfleet]

Originally Posted by VetteVet

If you guys have read my posts on this subject I have explained how the light and gauge are wired. Here is a diagram that shows the circuit board and how the light and gauge wiring is connected.


Attachment 1777002


Notice the dashed red line on the left that was connected to pin five on the light dash. The green wire that was connected there was moved to pin 6 for the gauge dashes, and nothing is connected there. It's one of the changes that has to be made when changing dashes.

It's already been said that the key grounds one side of the light when the key is turned to start. This is to test the light. It does the same thing to the brake warning light on both types of dashes.

I've got two gauge clusters and I'll have to check to see if the temp light came installed with them.

If that's the case, then the temp light will never illuminate with a properly wired gauge dash since no hot wire exists on the temp light circuit. (I have gauges and a gauge dash harness.)

I'm going to see if I can find a way to wire an oil pressure warning light switch to the currently unused temp lamp. Shouldn't it be as simple as wiring a oil pressure switch to the unused pin 5?

[StingRay]

Just find a no gauge harness and pull the wire that runs the light. Add it into the gauge harness. There is an empty spot for it. In the engine compartment same thing on that harness. Then run both the temp and oil senders to the same wire and you have your check engine light.

Originally Posted by Rich69shortfleet

If that's the case, then the temp light will never illuminate with a properly wired gauge dash since no hot wire exists on the temp light circuit. (I have gauges and a gauge dash harness.)

I'm going to see if I can find a way to wire an oil pressure warning light switch to the currently unused temp lamp. Shouldn't it be as simple as wiring a oil pressure switch to the unused pin 5?

[VetteVet]

Originally Posted by Rich69shortfleet

If that's the case, then the temp light will never illuminate with a properly wired gauge dash since no hot wire exists on the temp light circuit. (I have gauges and a gauge dash harness.)

I'm going to see if I can find a way to wire an oil pressure warning light switch to the currently unused temp lamp. Shouldn't it be as simple as wiring a oil pressure switch to the unused pin 5?

Yes if it has a bulb in it.and you use a sender from the light cluster in the oil port. The wire was originally connected to pin 1 on the light cluster plug

Look again at the diagram. The power for the cluster comes from the pink wire that goes to pin 3 on the plug then it feeds the fuel gauge, both warning lights and the temperature gauge. It is shown as a purple wire on the diagram but of course it is really a copper strip. The ground side of the temp light is pin 5 on the plug but it is not used on the gauge cluster. It grounds through the sending unit in the left head. And it is different than the sender for the temperature gauge.




Here is the wiring for the light cluster.

[Fraud]

I've got a different twist on this question - if my truck has been retrofitted with a guage dash, what do I have to change to make it work properly?

It was installed by the previous owner so I'm not sure what has actually happened... Currently it sweeps between about 1/8 and 1/4, and thats it. I'm wondering if the engine has the wrong kind of sender, or if I just need to swap out to a different pin per the diagram above?

I don't think its getting hot, but I'd like the gauge to work!

[Rich69shortfleet]

Well, there is already a wire in the harness that is going unused (the oil pressure switch wire). I just need to determine where it goes and instead route it to the unused pin 5 location.

[Rich69shortfleet]

I confirmed that the existing blue wire for what would be an oil pressure switch exists in the engine compartment harness, but terminates at the firewall bulkhead. There is no wire connected to it at the fuse panel. So, I added a wire so I can have that signal under the dash. I confirmed that the wire has continuity from the plug at the back of the engine to the wire I now have under the dash. I have an oil pressure switch I plan to add to the T fitting I have at the back of the block (I currently have a factory oil pressure gauge and and aftermarket oil pressure gauge, the oil pressure switch will replace the aftermarket gauge line since that extra gauge is an extraneous duplicate since I added factory gauges).

Now what I need to do is to run my new oil pressure switch to the cluster plug at the empty location 5. I can't see an easy way to add a wire here and have it make good contact with the printed circuit.

Does anyone have a hacked up cluster harness from which you could salvage one of the spring clips with some length of wire still attached for me? I do not have a spare harness, I sold my non-gauge harness with my non-gauge cluster. I really just need one clip in good condition with enough wire to splice into the wire I've already run from the engine. Any help would be greatly appreciated.

[Rich69shortfleet]

I've poked around and no one appears to sell these particular terminals individually so I again appeal to the membership here to help me find a terminal from the cluster plug I can use in my project. Any help that can be provided would be appreciated.

TIA

[davepl]

How does the ignition key ground the bulbs? I don't see a relay anywhere, and am not aware of a switched ground coming out of the switch (or is there?)

So when the purple crank wire goes hot, what grounds the bulbs during crank?

[VetteVet]

Originally Posted by davepl

How does the ignition key ground the bulbs? I don't see a relay anywhere, and am not aware of a switched ground coming out of the switch (or is there?)

So when the purple crank wire goes hot, what grounds the bulbs during crank?

It is internal in the switch and it is not connected to any thing else but the two lights.

[Rich69shortfleet]

Is there anyone who can help me locate a cluster plug wire contact?

[zosoppp]

This?

https://www.ronfrancis.com/prodinfo.asp?number=PC-12

also here:

https://www.classicindustries.com/pr.../bw900216.html

[Rich69shortfleet]

Originally Posted by zosoppp

This?

https://www.ronfrancis.com/prodinfo.asp?number=PC-12

also here:

https://www.classicindustries.com/pr.../bw900216.html

YES! I searched and searched and never landed on those. I guess half the trick is knowing what words to use in the search. Thanks!

[Rich69shortfleet]

Just a little follow up. I have successfully wired the TEMP light to an oil pressure sensor. I removed my aftermarket oil pressure gauge and retained the factory one. The oil pressure off the back of the block has a T, one side to the gauge, the other to the oil pressure switch. To me a lack of oil pressure is more important to have a warning light than an overheating issue. I watch the temp gauge a lot, I only watch the oil pressure gauge occasionally. I do like Stingray's idea of also wiring a temperature switch to this circuit to have kind of a check engine light function. All it would take is a temp switch and a bit of wire.

The first picture is the ignition on but engine not running so the oil pressure warning light (sic) is on. In the second picture the engine is running so the light goes out.

[67chevemall]

Nice job. And good show on the vacuum gauge.

[Rich69shortfleet]

Originally Posted by 67chevemall

Nice job. And good show on the vacuum gauge.

It's really only good for entertainment value. It wasn't expensive so I threw it in when I did the tach conversion install. Beats having a blank hole in the cluster.

[Rich69shortfleet]

Aaaaand the aftermarket gauges are all gone. Since I had to drain the coolant to remove the sending unit for the aftermarket temp gauge I figured I might as well install a temp switch and make my temp light a check engine light as suggested above by Stingray. I got a $9 switch, installed it and wired it and it works fine. I disconnected the oil switch and grounded the temp switch wire and the light turns on so wiring was good. I tested the temp switch before installing it and it closes when the switch gets above 250. That's really hot but at least good for a warning light.

It is so nice having those knee knocker gauges gone. The underdash wiring got a whole lot less cluttered too. The gauges have always worked great and were great to have when I didn't have factory gauges, but became redundant once I installed factory gauges. Same with the tach, was so glad when I switched to a factory tach and got rid of the tach I had on the column.