70ss with all factory gauges including tach. Just put the car back together. Temp is registering about 225deg. but engine does not appear to be overheating. Car has never ran over 185-190. One thing very curious though. When I turn off the ignition key the temp gauge goes all the way to the right past the 250 mark. Could it be a grounding problem? I also replaced the sending unit. Maybe they gave me the incorrect one. PC board is also new. Any help greatly appreciated.

I would definitely check the ground and make sure the connections are very clean. No paint at the ground etc. I hope this helps.....

One thing very curious though. When I turn off the ignition key the temp gauge goes all the way to the right past the 250 mark. Could it be a grounding problem? I also replaced the sending unit. Maybe they gave me the incorrect one. PC board is also new. Any help greatly appreciated.
Were the gauges added? Sounds like the circuit is still getting power with the key off. Does it move slowly to 250 or quickly? Try disconnecting the sending wire and turning key off, does it still peg to 250? As for the gauge reading high there were some posts on that subject with replacement sending units and how to correct. Do a search on Steve S and Elree Colby, one of there posts had a solution.

These are all factory gauges. It's a one owner factory SS car my Mom bought in 1970. She asked me to pick her out a car that would get her through intersections and across roadways quickly and still have some "get up and go" if needed.....sorry, back to the issue. I disconnected the wire to the sending unit..turned ignition on..no response on gauge. That's good. I reconnected the sending unit to green wire..Now gauge is climbing to about 220-225deg. Problem with gauge passing 250 mark when ignition is turned off has stopped...hummm. I believe sending unit may be causing high reading problem. I will go to the website you indicated for information. Let me know if you have any other ideas...Thanks...Wayne

Oh boy! When I turn on park lights with key off, temp neddle goes well past 250 mark easily. If I turn key on with park lights on, temp neddle resets but if I turn key off temp neddle goes back past 250 quickly. Seems like theres some voltage getting where it shouldn't via lights....Help!

70ss with all factory gauges including tach. Just put the car back together.
Explain everything you had apart and put back together in the dash area, might give a clue to you problem. Your right, seems like the temp gauge is getting power via the dash lights, maybe Steve S will chime in.

I removed the whole front of the dash to easily access all gauges and a/c vents to replace printed circuit on back of gauge cluster and deteriorated a/c vents. Everything works fine except temp gauge...Thanks Greg...any other input is greatly appreciated....Wayne

My guess is cluster ground is not connected. Did you reconnect the cluster ground wire. There should be a black wire with a ring terminal attached by one of the cluster screws. This (http://www.chevelles.com/showroom/data/516/70_72SSclstgr.JPG) pic shows a good location for the ground wire.

I did connect the cluster ground but it's possible the ground may not be good enough. I'll check that first. I'll see if I can get an alligator clip on it with a good source ground and see if that solves the problem......Thanks

The temp and fuel gauges are attached to a separate meal back plate. It is grounded to the main cluster back plate by a trace on the circuit card. This (http://www.chevelles.com/showroom/data/516/temp_fuelgagrd.jpg) pic shows the two screws that provide the ground for the temp and fuel gauges.

Oh boy! When I turn on park lights with key off, temp neddle goes well past 250 mark easily. If I turn key on with park lights on, temp neddle resets but if I turn key off temp neddle goes back past 250 quickly. Seems like theres some voltage getting where it shouldn't via lights....Help!

grounding problem for sure. Can you make the temp guage go up and down by turning the headlight switch? (making the dash lights bright or dim)

The headlight switch makes the temp needle go up but it takes turning ignition on to make it go down. If I turn key off and leave light switch on the temp needle goes up again. I'm not sure but I figure that"s maybe resistance from the poor ground....Great pics EC....Jim, I didn't notice the lights dimming. I sure appreciate the suggestions and help. There's a front dash mounting bracket just above the steering column and most of my grounds are tied there...That's the next move....Thanks fellas....Wayne

Well, here's the lowdown. I checked existing grounds and re-tightened them. I installed gauge cluster. With lights on and key off temp climbed slower and to about 210deg. I then decided to run a ground from the temp gauge lower center post (-) and one from one of the pc board grounds to metal frame. Now when I turn on lights with key off the temp only goes up about 8-10 degs. Now when I run engine about 15mins, temp gauge reaches about 210deg instead of 230. I'm going to add another ground to see if it will cancel out the other 8-10deg and hopefully lower my total temp with engine running. I have also ordered one of the sending units from lectric limited inc. to see if it gets me back to the original 185-190degs. I will post the results as I make the changes. FYI my temp gauge has the orange resistor intact. Thanks,blwn68, undees 70 ss and elree colby for the posts...Musekkman.

I attached one more ground to the gauge cluster metal housing. I've also installed new temp sender unit from lectric limited. My temp gauge now reads correctly, two marks left of 210deg mark. This is where my temp ran continuosly previos to putting another aftermarket sending unit. Lectric limited was evidently correct on resistance matching their unit. Kudos to them. Thanks for all the help everyone.....Wayne

:thumbsup: Glad you got it working. Thanks for posting back the info, sure it will help someone.

How many grounds do you need on the cluster? as I put the 71 dash in my 70 El Camino I found 3 ground wires in the harness, I believe that 1 went to the light switch and the others grounded the cluster. I have run a ground wire directly to the cluster to the brackets that are welded to the body. and as I check my voltages at the cluster connector I can use the back of the cluster as a ground on my test light. and I still have "ground problems" none of my gages, tack or clock are working and my clock is new. some lights are working. have an hei dist. Does the bottom of the temp gage need grounding seperately?
Phil

I would consult the factory wiring diagram and see what the cluster calls for. Sometimes they do things a little different from year to year..