I have given up on my factory dash temperature gauge. It moves ... I've adjusted the pointer ... replaced the temp sending unit, but it doesn't read correctly. Rather than pursue attempting to fix an old gauge I'd rather just add a second temperature gauge. I've done this with my GTO and Formula as I don't trust the older gauges. Is it possible to add another gauge to my set up?
1986 GT with 3800SC and spd. I haven't checked out the engine/heads to see if there is a plug that can be removed to install a secondary temperature sensor to run the additional gauge. Does anyone know if the 3800 has another area where I can install a temp sensor? I don't want to remove any engine components to drill and tap a place to install. Luckily, older engines had plugged, threaded intake manifold or head ports that could be used for this.
I've replaced the factory 3800 sending unit with a Delco replacement. Is it possible to use that and just bypass the factory gauge. As I recall from memory (dangerous at my age) there are three wires for the sending unit. One goes to the PCM and I assume that the other two are for the gauge? Is it possible to use these two to operate an aftermarket gauge? The resistance from the sensor would need to be compatible with the aftermarket gauge.
Thanks in advance for your input.

If you go for an Autometer electric gauge you just need to drill and tap a 1/4-20 hole to thread the sender into. The autometer gauge won't work with the GM sender. I put mine directly into the top of my 3800 T-Stat housing.

There are also gauges that plug into the OBD-2 port ( Aero Force ) That can display tons of info.

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1986 SE 3800SC/4t65eHD (12.871@104.96) I'll Sell it if you like
1985 GT 3800SC (swap in progress)

My t-stat housing already has a threaded port that has a plug in it. Perhaps I'll take out the plug and determine with bore size and thread it uses. Might get lucky and find a direct bolt in? Anyone know what size and thread goes in this t-stat housing?

The 3-wire sender uses yellow and black for the PCM and light green for the gage.
The gage provides 12v to the sender, the sender varies resistance to ground based on temp.

The factory units (when repaired/calibrated) are probably more accurate than a cheap aftermarket gage.

I would replace the gage or have someone repair/calibrate it.