Hello I am trying to install an aftermarket electric water temp gage on my 1987 camaro v6 because it didnt come with one. I tapped into a dark green wire from the temp sender, tapped into 12V crank from the fusebox, and connected the gage to ground. Currently, when I turn the ignition on but dont crank, the needle resets to 0 but does not move again and read temp when I turn the car on. Also, when I turn the ignition on, my dummy lights for oil pressure and volts turn on, but my dummy light for coolant temp does not turn on. Is this a sign I need to replace the coolant sender?

 

Turn the key on, disconnect the green wire from the sending unit, and ground it. The gauge should go to full scale. That will verify the wiring & gauge.

If you didn't already change the idiot light switch out to a gauge sending unit, then of course it won't work right. All that such a switch does is stay open (disconnected for all practical purposes) when the temp is below the idiot light turn-on temp, and become a short to ground when it gets hot. A gauge hooked up to such a thing will read either 0 or maxed out; nothing in between.

Also of course, if the light sending unit is disconnected, such as if you hacked its wire, then it can't possibly work; except that the part behind the dash is probably still there (I'm guessing that, since it's MUCH harder to get to, and rarely gets hacked on), and therefore it should light via the "bulb check" function when you turn the key to Start.

 

Your not going to get a gauge to work with the temperature switch that controls the coolant temperature light.

Notice how I said "switch", and not "sensor" or "sending unit"?

That unit is exactly that, a switch, a "thermal switch" to be exact. That switch remains "open", as in it's not a path for electricity, until the coolant reaches a temperature that is considered overheating. At that point, the switch closes it's normally open electrical contacts and grounds the dark green wire to light up the coolant temperature light. The only way to get the gauge to read the actual coolant temperature is to install the proper sensor (or "sending unit", call it what you will) that is specifically designed to work with the aftermarket gauge you are trying to use. If you don't mind loosing the coolant temp "dummy light" you can install the proper sending unit for your new gauge in where the switch now resides for the light. While doing so, you'd be best served to run a dedicated wire from the new sensor to the gauge and not use the existing dark green wire that becomes a hard short to ground while the key is in the start position, this was fine for testing the coolant temp bulb, and factory gauges are designed to withstand the 0 ohm peg to full scale test, but I'm not so sure if your aftermarket gauge will appreciate the same treatment.

Lastly, all of the other sensors (sending units) and thermal switches that are screwed into the engine to measure the coolant's temperature have important functions and must not be removed to install your new gauge's sensor, use the one that (used to) control the coolant temp light, even if it happens to seem that one of those other units may be an easier place to install your new sensor......

And I see Sofa beat me to the post by mere minutes......

 

Ok, aftee further fiddling I did what you said and turned the key on, and disconnected the green wire from the sender and grounded it, and the gage went to max. So I assume theres no problem with the gage or the wiring. Also the aftermarket temp gage didnt come with a sender, its a universal gage, so I tapped into the original sender via the dark green wire and ran it to the gage. Thank you for clearing up the dummy lights, I was just thinking if the temp sender is faulty.

And correct me if Im wrong, i was under assumption that sendors, not sensors, do not affect the ECM and only send info to a gage.

 

Senders (with an e, not o) are unrelated to the ECM in any manner way shape form or fashion. The temp gauge one in GM cars has been the same, electrically, since the early 50s, that I know of; maybe farther back than that although I wasn't payign much attention to that sort of thing in WW2 era vehicles I was working on. There have been acoupla variations in the threads where they screw in, butt the basic function has remained the same. Now of course, it may well be that those clever GM engineers wanted to fake those g00bz at Frod and Xler about introducing EFI 30 years or so into the future after their casting design, as we all know that they did by disguising the small block V8 knock sensor port as a coolant drain starting in 1955; butt, however all that may be, the temp gauge and the ECM's temp measurement are completely separate, up until the late 90s when they went to digital communication between the ECM and the dash.

 

What you have installed in your engine for your tell tale light is a temperature switch, much like a light switch in your house. In your house you flip the switch and the light comes on. In you car there is a snap action thermo switch that snaps on when the engine get too hot and turns on the tell tale light on your dash.
You need to swap this temperature switch out for a temperature transducer that varies its resistance to ground depending on the motor temperature.
On my 1986 V6 this temperature transducer is located at the rear corner of the V6 motor on the passenger side. I'm guessing that is the same location that your current temperature switch is at.


These temperature transducers are available from several manufacturers under these part numbers I believe, but check for yourself to be sure. Look for the transducer for gages.
Wells

1T1041

Standard Motor Products

TS88

BWD/Niehoff

Part number WT366

Swap out the temperature switch in your engine for a temperature transducer and connect the wire from the transducer to the new gage.
You may have to drain the coolant from your engine so that you don't end up with a mess on the floor.
The radiator drain plug is at the bottom of the rad on the passenger side.

 

Thanks for info, I ended up ordering a temp sender from the same place I got the aftermarket gage, installed it where the sender or transducer was and ran the wire from the sender to the gage and it ended up working. I believe the old sender was just old and crap

 

Well, I'm happy to hear you put the correct sending unit in it, and it works.....

But, just to be 100% clear here, the original thermal switch was not "just old and crap" , and would have functioned as the factory installed it to, provided the rest of the circuit was intact.
Had the engine overheated it'd (eventually) have turned on the coolant temperature warning light, just as Sofa and I described it's normal mode of operation.

Your modification of installing a Gauge VS the warning light necessitated the use of the correct sending unit for that gauge, this is not the fault of the original thermal switch.......

 

Not sure why this quote didn't make it into my above post