1986 FC n/a possible electrical problems
 

Hey guys, for some background, not only is this my first rx7 it is also my first fix up car so any advice is greatly appreciated.
I'm fixing up an old 86 rx7 FC n/a and though it runs and drives great, there are some minor fixes i would love to settle.
First, the horn does not consistently work. i would say about 50% of the time it ranges from working for a whole car ride and then the next time in not working at all. I checked the fuses and all looked good, but i read somewhere it could be in the CPU and any extra help on that would be appreciated.
Next is the a/c. Doesn't seem to be working at all and i tried to recharge it but the nozzle wouldn't fit. I dont even have an idea what this could be so any type of advice on it would be awesome.
Lastly sunroof doesn't work and i discovered it is a problem of a broken plastic part that pushes the sunroof up and down to open and close respectively. I would like any advice on this as to where i could purchase this?
Other than those problems car just needs some paint work before it will be absolutely flawlesss! thanks!

Find the largest plug to the CPU and then find the Green/White wire and check for constant voltage (no key needed). Also, place a ground to the Green/Orange wire in this plug and the horn should sound out each and every time. Does it? The Black wire in the same plug is a ground. You can jumper a wire from this ground source to the Green/Orange wire.