Temperature gauge

[Nick F.]

I've been reading thru the search on temp gages in both discussion & archives to find a test for my problem. I recently purchased a new temp sender with calibrated resistor from LIC for my 65 396 (NOM; had an aftermarket gauge installed). After finding the green wire on the firewall, I soldered the necessary connections and plugged the 2 prong connector into the gauge under the dash. The needle at that point was in the center at 210. When I turned the key on, the needle pegged way, way beyond the 260 range. I immediately cut the power. I disconnected the the wire from the sending unit but nothing changed. Do I have a direct short to ground or simply a bad gauge? Are there specific test procedures I can do to find the problem?

[Bob M.]

Re: Temperature gauge

I recently had the same problem. I tried everything that was helpful in my recent post. My gauge is original, I'm not familuar with the after market gauge. I changed out the tach, speedo and trip, there was nothing wrong with the other gauges. Once I applied voltage, the temp gauge went to the right. The original gauge, once the water temp got hot, stayed at 160 degrees, now it is reading 220 degrees. I am still working on that problem. I added a new ground wire which made the gauge work like it is suppost to, but I don't like the 220 degree reading. I have to find a solution to that problem. I can only suggest adding a extra ground wire to the cluster. It worked for me.

[Nick F.]

Re: Temperature gauge

Bob, I actually was trying this when I looked at your email. Unfortunately, it didn't work for me. However, I did find a Black with Pink striped wire that was just hanging near the ignition switch located near the temp gauge. As I tried to trace the wire using the crude schematic I have for 65 corvettes, I noticed that this wire does go to a junction point that may energize the temp gauge & fuel gauge (noticed that wasn't working either. Problem is, I don't know where the bare end come from. Is it part of the ignition switch? Any help would be very appreciated.

[John H.]

Re: Temperature gauge

I did find a Black with Pink striped wire that was just hanging near the ignition switch located near the temp gauge. As I tried to trace the wire using the crude schematic I have for 65 corvettes, I noticed that this wire does go to a junction point that may energize the temp gauge & fuel gauge (noticed that wasn't working either. Problem is, I don't know where the bare end come from. Is it part of the ignition switch? Any help would be very appreciated.

Nick -

That 18-ga. black/pink wire comes off an internal splice in the dash harness; it's fed from the top fuse in the fuse block, and the four black/pink wires from that splice feed power to the temp gauge, gas gauge, parking brake warning light, and to the fuel tank sending unit for the gas gauge. Those are the only items on that fuse.

[Nick F.]

Re: Temperature gauge

John, it order to reconnect the bare end to the internal splice, am I looking under the dash around the ignition switch for the splice point where 4 B/P wires come together? Being that my temp gauge & gas gauge don't work but the parking brake warning light does, can I assume that this 18-ga B/P wire may be the culprit? Does this wire carry any voltage, key on or key off, or is it a form of a ground? I just don't want to hook it up, in the wrong place, and cause more damage than I bargained for.

[Bob M.]

Re: Temperature gauge

Adding the ground to the cluster wasn't the answer for my problem. Yesterday, I put the old sensor back into the intake, the gauge went to the right again. I took the green wire off the sensor a couple of time, the gauge went to the left and stayed there. I don't think that I have the problem solve yet. I am going to the Regional next week and will be asking a lot of question to resolve this problem. The top of my old sensor is loose where the new one doesn't move, but both act the same when power is put to the gauge. If I find something that I feel works I will contact you again.

[Nick F.]

Re: Temperature gauge

Bob, at least your gauge moves left or right. I remember reading in the archives about adding a resistor in line with the sensor. I think it was a 60 ohm 1/2 watt resistor bought from Radio Shack. If you search in the archives under temperature gauge, you'll probably run across it. They may help your situation. I believe in my case that the nasty little 18-ga. B/P wire has something to do with my mystery. I'll keep working on it until it solved....hopefully!

[Gary C.]

Re: Temperature gauge

Bob, go to Radio Shack and buy a 60 ohm resistor. Remove the wire from the temp sensor. Connect one end of the 60 ohm resistor to the temp sensor wire and the other end to a good ground. Per Jack Humphrey a 60 ohm resistor to ground should cause the temp gauge to read pretty close to 230 degrees. Gary....

[Bob M.]

Re: Temperature gauge

I am working with an original gauge that works, but there is still a problem and I shouldn't need the resistor. I understand that the repo's need the resistor. I hope you find your problem, I won't give up on mine. If I get my problem re-solved I will post again.

[Bob M.]

Re: Temperature gauge

Gary, I will get the resistor Monday. I just don't understand why one sensor reads higher than the other when they are working. Maybe the resistor will help me find the problem. I did nothing to the gauge when I worked on the cluster because it was working at the time. Only the tach and speedo got changed. See you at the Regional. Thanks for the suggestion.
Bob

[Nick F.]

Re: Temperature gauge

Nick -

That 18-ga. black/pink wire comes off an internal splice in the dash harness; it's fed from the top fuse in the fuse block, and the four black/pink wires from that splice feed power to the temp gauge, gas gauge, parking brake warning light, and to the fuel tank sending unit for the gas gauge. Those are the only items on that fuse.

John, does the bare end of this 18-ga B/P wire get connected to the ignition switch? The wiring diagram I have is somewhat hard to read but I think it's showing a B/P wire(s) going to the ignition switch. If so, which terminal does it go to? Any ideas???

[John H.]

Re: Temperature gauge

John, does the bare end of this 18-ga B/P wire get connected to the ignition switch? The wiring diagram I have is somewhat hard to read but I think it's showing a B/P wire(s) going to the ignition switch. If so, which terminal does it go to? Any ideas???

Nick -

That wire shouldn't have a bare end. The top fuse is fed from the ignition switch by a black/pink wire, and the output side of the fuse has a black/pink wire that terminates in a 4-way crimped and soldered splice bar inside the harness wrapping. The four black/pink wires from that splice feed the four items I noted above; one goes to the gas gauge connector, one to the temp gauge connector, one to the "Brake" warning light bulb socket on the back of the cluster, and one wire goes to the multiple connector body above the driver's side kickpad that plugs into the mating connector on the rear body harness to feed the fuel tank sending unit.

All four of those black/pink wires are "hot" when the key is in "On" or "Accessory".

[Nick F.]

Re: Temperature gauge

John, what happened is the previous owner installed his own Vintage AC system. What I think he did was cut and splice a few wires here and there that's why I'm ending up with a bare ended 18-ga B/P wire that goes somewhere around the ignition switch. The wiring diagram of the ignition switch is showing the following:
12-ga R to BAT, 14-ga BRN to ACC, 14ga-PPL to SOL AND 2 18ga-B/P to IGN side of switch. I have the Red wire, the Brown wire and the Purple wire and a yellow wire that was added by previous owner. I have NO B/P wires on the switch. Is this B/P wire (with the bare end) that's hanging near the switch go to the IGN side of the switch, so it can power my temp & gas gauge along with the brake warning light? I may have accidently pulled that wire out of the switch while trying to get my hand up to the temp gauge connector but I can't be certain. The unfortunate part is that it doesn't have a spade connector on it, just a twisted 1/4" stripped end so he must have simply jammed it together into the switch or connected it to another wire.

[Ronald L.]

Re: Temperature gauge

On the topic of these erratic temp gauges...

I did the same last year, all new correct calibrated parts, bench tested and in the car the new gauge pegged out and that was it. After lengthy probes and experiments, I had no real answer why that LIC set up failed.

I ended up using the original gauge and one of two original senders I have from the L36 cars I have owned.

But - here is the trick. And some if not all was posted earlier this year as I went at this problem, with some of John's great writings to help along the way.

Step by step you need to isolate the circuits.

First - set all this up outside the car.

Take a cup of water, on a hot plate or stove and with a multi meter & clips - yes it is hot - check the resistance. Different articles will have different values for what your sender should register hot - boiling water is 212 at that is going to be as hot as you need. The key I found is that one of the three senders was SLOWER than the others to register that resistance in boiling water.

Now that you know the sender works, get that gauge, take a hot lead from somewhere like the glove box light, run that to the appropriate terminal on the gauge (not the entire cluster asy). Run the lead from the ground terminal to the radio chassis - this is going to emulate where your ground actually terminates in vehicle. Run the other wire to the sender, you need to use an alligator clip as this will be hot and you have to hold that in the water as you run the temperature up to 212. Get a big alligator clip on the ground side of the sender and run that back to ground, battery for now.

As you run the temp up, you should see your system work, if it registers 210 when the water is boiling, you are better that the specs on this gauge as it is not linear.

Now, start to replace circuits. Find the two leads from the dash connector, run the hot one to the power side of the gauge. Repeat. If you get 212 keep going. Note that you still have the gauge grounded through the radio chassis and the sender to the motor or battery. If you find changes from top of motor to battery faulty grounding is indicated in these areas.

The next test should be gauge powered from connector, green wire in terminal to gauge terminal, and ground pin to radio ground. For this test you need to go underhood to the end point of the green terminal, clip on there and to the top of the sender. Heat it up. If you get 212, you are very close.

The next test is to put the sender into its position, green clip on. Now you can start the car and bring it up to temp. At this point the only part that is not is its intended position is the gauge - but - it is using all the intended wiring.

I did this set of tests to avoid pulling the cluster - again - only to have it not work. In fact - with a couple of leads the gauge sits down by the console and works fine until the snow flies.

If it does not work when in the cluster - we have bigger issues and we will know where they are, ground out of power to green wire or or greenwire to ground terminal (MO) are top indications of why the new calibrated parts blew to infinity.

[John H.]

Re: Temperature gauge

I have NO B/P wires on the switch. Is this B/P wire (with the bare end) that's hanging near the switch go to the IGN side of the switch, so it can power my temp & gas gauge along with the brake warning light?

Nick -

Yes, the black/pink wire goes to the "IGN" spade on the ignition switch; with it hanging as you noted, none of the four items I mentioned that it feeds should be working, and there should be no power on the outboard (input) side of the top fuse.