Search:

The Amp Hour rating quoted is usually the 20 hour rate: you can get 5A for 20 hours.
The discharge rate for one hour will be considerably less.

As 97_gq_lwb says, the device on the firwall is for the Air Conditioning idle up. It is just a solenoid operated switch for vacuum.
Do you have a cylinder attached to your injector pump throttle...

It is a breather.
Don't worry to much about it. If you have that breather then your sender has most likely been replaced already, and this type is more reliable, than the original.

OK, how about a short in the combination switch. Disconnect the headlamps and see what happens.
After that, it may be time to divide and conquer - cut the wire going rearward, or through the...

Radio / Stereo ??

Yes, it fits in the groove in the lid, that the base fits into.
The original is just some foam rubber. or you can get an o-ring from CBC p/n BS445A

B = Black
BR = Brown
W = White
OR = Orange
R = Red
P = Pink
G = Green
PU = Purple
L = Blue
GY = Grey

What relays are switching ON / OFF - you probably need to get a location even if you do take it to an auto-elec.
Is your key / ignition barrel worn - could be removing the key before the switches...

You'll be right with those spots, especially as they are easy to do.
EGT is arguably better pre turbo, but requires more effort.

Everything bar the engine mechanical and electrical should be right.
I have attempted to get a manual that includes the RD28T, TB42E & RB30, but no luck yet.