I'm thinking of getting an Auto Meter water temp gauge, electrical, and not sure which sensor in the motor is responsible for the stock gauge in the cluster.

 

It's the one right next to the oil pressure sender, underneath the oil filter

 

I forgot to mention that I have an '85 GSL-SE. Does this make a difference compared to a 12A equipped car?

 

The 12A water temp sensors are on the driver side of the engine, right underneath the beehive oil cooler. You'll see a large brass colored bulb that is threaded into the engine. That's the oil pressure sensor. Right in front of that is the water temp sensor. It will have a bullett style electrical connector on it, and I believe that a 12mm socket will fit it....

Never owned a GSL-SE, so I can't help much in that aspect. Hopefully this is some help to you...

 

Thanks for explaining the 12A's location, but since I don't own a 12A (and will ensure I never do; I hate carbs) it's not much help to me.

I know there are three sensors: 1 at the top of the radiator, 1 at the bottom left, 1 near the thermostat housing.

 

All engines have the temp sensor for the gauge next to the oil pressure sender. You will need to buy an adapter fitting to fit any of the aftermarket temp gauges snnce the threads in the block are BSPT.

Since you have an SE, your best bet may be to tap for a new fitting next to the one on the backside of the waterpump housing.

 

I have a website that offers BSPT to NPT adapters. So, that shouldn't be a big deal, however I wonder what the actual size is. If it's 1/8, Pegasus Racing and Re-Speed offer an adapter. Anyone know of the water temp fitting size?

So, if the temp sensor is in the same location for 12As and 13Bs, what are those 3 other sensors that I talked about before?

 

The one at the top of the radiator is for the coolant level warning.
The one at the bottom left is part of the emission system and if memory serves me retards the timing at some point.
The one near the T-stat housing is the coolant temp sensor for the ECU.

 

I miss my old Chevy pickup when engines were made simpler. ^^ (Read: '90 pickup)

 

so which one is responsible for the gauge in the car mine went to heck and i cant figure out why? here today gone tomorrow??

 

the one by the oil filter is for the gauge