krthorp

My 1966 temp gauge does not register any temp. The needle lies way below the 100 degree mark but moves to the 100 degree mark when the ignition is turned on. The needle does not move from the 100 degree mark when the engine is running. Is there any easy way to determine if the problem is with the gauge or the sending unit. I am a non electrical guy so I need some information I can understand. Thanks for any help.

Nowhere Man

If you unplug the sending unit the needle should stay at the bottom of the gauge

cblankin

Have you tried removing the wire going to the sending unit with the ignition switch in the on position and ground the wire to see if the temp gauge will deflect all the way to the right? That should tell you of the gauge is working. Have you check the bulkhead connector to see if the contacts in the connector are corroded. Be careful not to break the connector. The connector ears are brittle. I an having a problem with my needle not going past 110 degrees.

Randy G.

Unplug the wire on the sending unit, turn the ignition on and ground the wire from the sending unit to a bare metal part on the engine. That should peg the gauge. If it doesn't, it's the gauge or wiring to the gauge. If it does, change the sending unit.

Randy G.

Looks like cblankin beat me to it by mere seconds. LOL

65GGvert

If you turn the key on, doesn't need to be running, pull the wire off the top of the temp sensor and touch it to a good ground (initake, valve cover bolt, something non painted like breather mount screw). The gauge should peg full hot. Don't leave it there, just touch it momentarily and have someone watch the gauge. If it does, the problem may be in the sender. If it does not peg when grounded, you could have a bad gauge or a bad connection in the bulkhead connector below the master cylinder. If the green wire that passes through there is corroded, it will cause what you are seeing. It's in the connector that's closest to the centerline of the car. The pin will be the second one from the bottom on the right hand side as you look at the bulkhead. If you CAREFULLY release the plastic tabs and pull that connector off, take a look at that pin in both sides of the connector to make sure that the pin hasn't pushed in at some point when connecting, and also check for corrosion on the pins. If you have corrosion, disconnect the battery and spray some contact cleaner in there and use a toothbrush to clean it up.

If the gauge does peg when you ground that green wire, then use an ohmeter to measure from the top of the sender to the engine ground I mentioned earlier. In normal garage temperatures it should read about 600 ohms to ground. If it reads much higher, you may have a bad sender, OR the sender may not be making good connection where screwed into the manifold. You can eliminate that by touching a ground jumper from the base of the sender to the same engine ground I mentioned earlier. With the key on, green sender wire connected, if your temp gauge moves AT ALL, you need to unscrew the sender and clean up the threads and reinstall. You don't need to use any tape or sealant on the threads.

If you'd like help step by step, first turn on the key and touch the green wire to ground and post back what you get and we'll go from there. Again do not leave the green wire shorted more than momentarily, and do not leave the key on with engine off for an extended time.

The gauge needle could be the problem, but let's do a step at a time.

65GGvert

I guess I took too long typing.

Oaker57

Frankie the Fink

Because your troubleshooting approach is detailed and thorough...

65GGvert

krthorp, what's the latest on your temp?

krthorp

Thank you all for your help with my temp issue. With your help I was able to determine the problem was with my sending unit. A new one is on order. It's nice to have knowledgeable people out there.

Oaker57

I found the opposite result, when grounding the sending unit wire, my needle stayed stuck at 110....so I am going to assume it's a bad gauge. I am also assuming that the cluster must come out to change the temp gauge......not looking forward to that..

Early66L72

oaker57, the cluster does not have to come completely out BUT it is still going to be a PIA to change. you will need 5-6 6 inch 1/4-20 long bolts with the heads cut off, the ignition switch removal tool, and then you can go after it. i had to remove my clock as well and that helped get my hand inside to remove some of the screws. there is a thread here on the process, just use the search. if you can't find come on back and i'll post some pics..

good luck

jcw

65GGvert

Also make sure that your firewall connection where the green wire goes through is not corroded or has a pin pushed out or a wire broken. It's on the inside connector on the bottom right, 2nd pin up. If that connection is bad, or if you have a break anywhere in the green wire your gauge won't move when you ground the wire on the sender. It also won't move if you don't have 12 volts going to one side of the gauge.

popbluff

do they make two different sending units one for the temp gauge and one for the cars with just a temp light does it make a difference on the way your gauge reads if you have the wrong one, and how can you tell the difference between the two

krthorp

I've only had corvettes with the gauge not with a light so hopefully someone else can answer your question.

65GGvert

I've never had one with a light. I've had success with a Duralast TU-5 from AutoZone

JohnZ

Midyears used the #1513321 sending unit originally, with the "nail head" terminal for the connector. Corvettes never had a light.

Oaker57

I will double check the bulkhead connector, but I'm pretty convinced it's the gauge itself, because when it first started to stick, it would respond when I tapped on the face. But that only lasted for a while, and it now is stuck at about 110, and responds to nothing anymore.......

65GGvert

If it stays at the same temperature hot or cold is most likely the gauge.