84 GPZ550 Electrical Probs

Hey guys im a newbie on here but not new to bikes. Its been a long time since i had one until one day at work a guy i worked with told me he had an old 84 GPZ550. I remember these bikes when they first came out. Anyway we got talking and he said he dropped it while riding one day and tore up the plastics, fairing etc so he took them all off the bike and dumped them with the intention of replacing them. He said the bike bike had stood in his shed for almost 6 years and just never got round to doing it. I asked him if he wanted to part with it so we struck a deal and i now own the bike.

After getting the bike home and cleaning the cobwebs of it i got a new battery and charged it to see what was what. The starter worked and the bike turns and yes i did put a small amout of oil down the plug holes and let it settle overnight before doing this. I already had the carbs off ready for stripping so i didnt try to fire it. I tested each plug and im getting a good spark from all them of them, so far so good, which means once the carbs are done the bike should run.

Now for the mess lol. I tried the other electrics and nothing. No lights, no blinkers, no neutral light, no horn, no nothing. After cleaning all the harness and contacts and plugs i managed to get the hazards working. so far thats it.
There is no headlight and blinkers on the bike as yet but i did test with a meter and using a bulb so i know the hazards work and the warning lights for them is working.

Not working is- rear light, brake light, blinkers, neutral light, clock lights, horn and fuel tank tank display. there is no headlamp so ive not tested that.

Ive tested the LH switch gear and all switches are working from the switches to the connector plug.
Ive tested most wires in the harness from front to back so all seem ok, and connectors etc, all seem to be fine and tested ok, tested both flasher units via the hazards so i know they are both working.
So my questions are this,

Should these items all still work with the tank display disconnected?

Should these items still work if the regulator/rectifier is faulty or disconnected?

What is the reserve lighting thing? and should these items work if that is disconnected or faulty?

What is the little thing next to the flashers its rectangle shaped with a six pin connection and is black at the top and has what looks like a number 30 on it. Is it a fuseable link or something and what does it do or protect.

To the right of the flashers there is a black sleeve with what seems to be a realy inside, what is it for.

I have one brown wire unconnected right next to the coil what is this for? where should it go?.

Please see attached pics. It know its alot of questions but most are a case of if i disconnect these items should the rest still work kinda thing. Im waiting for a manual comming and have download a wire diagram but its small and some of the colors dont match up and the pos and neg on the batt on the drawing is back to front so i dont trust it a whole lot. Many thanks in advance to any help given. I would love to get this old bike going again it brings back so many good memories.
PS i have replaced the 3 fuses in the fuse box and test both sides so fuses and box are good.

Thanks Peter