Tach is powered indirectly form the fuel pump relay, and they are part and parcel. Clean your grounds Frame to engine, and engine to tranny or better replace them.
The over heating is probably but not limited to.
Air Bubble at the t-stat, if you drill a 1/8 inch or 1/16 inch hole in the lip of the t-stat you don't have those issues.
They make a 180 t-stat.
To fill without drilling a hole, you have to loose the upper hose from the Radiator and the outlet on the head. You will fill it from the head side first until it bac fills the hose a wee bit, then take the hose and reverse it and fill the radiator.... once you have fluid dribbling out, then reconnect the hose and fill the expansion jug.
Squealing can be a bad bearing in the pump, and if you haven't replaced it yet you may want to order the housing and the water pump together.
You also need to loosen each bolt one at a time on the wp and coat the threads with never-sieze then replace and re-torque to 87 in/lbs.
Squealing can be a belt that is wet or oily that is as it is prone to road wash.
www.cabby-info.com is a good source for part number information.
If you have a/c then you would need a 2 speed fan.
The power is from the battery to the radiator switch, from the other side up to the fan, and a separate ground is required. Make sure the fan runs by jumpering it to the battery.
You may want to place a 20amp fuse in the circuit.
If you haven't flushed and back flushed your radiator and block you may want to to validate that it is clean as it has been sitting.
In the DIY's above there is a thread on it Backflushing your radiator, and then there is a how do I replace my water pump thread as well.
Also if you don't have an upper radiator card installed it can and will allow re-cycled engine compartment air over the radiator at a stop.
You can see no radiator card.

Radiator card.

This will dramatically reduce engine operating temps at a stop.
https://volkswagenownersclub.com/vw/showthread.php/21830-How-I-change-out-my-Water-Pump
https://volkswagenownersclub.com/vw/showthread.php/21399-How-to-flush-your-radiator
The over heating is probably but not limited to.
Air Bubble at the t-stat, if you drill a 1/8 inch or 1/16 inch hole in the lip of the t-stat you don't have those issues.
They make a 180 t-stat.
To fill without drilling a hole, you have to loose the upper hose from the Radiator and the outlet on the head. You will fill it from the head side first until it bac fills the hose a wee bit, then take the hose and reverse it and fill the radiator.... once you have fluid dribbling out, then reconnect the hose and fill the expansion jug.
Squealing can be a bad bearing in the pump, and if you haven't replaced it yet you may want to order the housing and the water pump together.
You also need to loosen each bolt one at a time on the wp and coat the threads with never-sieze then replace and re-torque to 87 in/lbs.
Squealing can be a belt that is wet or oily that is as it is prone to road wash.
www.cabby-info.com is a good source for part number information.
If you have a/c then you would need a 2 speed fan.
The power is from the battery to the radiator switch, from the other side up to the fan, and a separate ground is required. Make sure the fan runs by jumpering it to the battery.
You may want to place a 20amp fuse in the circuit.
If you haven't flushed and back flushed your radiator and block you may want to to validate that it is clean as it has been sitting.
In the DIY's above there is a thread on it Backflushing your radiator, and then there is a how do I replace my water pump thread as well.
Also if you don't have an upper radiator card installed it can and will allow re-cycled engine compartment air over the radiator at a stop.
You can see no radiator card.

Radiator card.

This will dramatically reduce engine operating temps at a stop.
https://volkswagenownersclub.com/vw/showthread.php/21830-How-I-change-out-my-Water-Pump
https://volkswagenownersclub.com/vw/showthread.php/21399-How-to-flush-your-radiator