The stop solenoid uses a lot less than 20 amp, but if your immobiliser just interrupts this supply I wouldn't bother as a common theft method is to just run a 12v supply direct from the battery to the solenoid. I would consider fitting another solenoid out of site for the immobiliser to operate.
If you identify the earth on both the vehicle loom and the light unit the others are easy to identify with either a multi meter or test lamp. You should not need a wiring diagram.
Personally I would cut those Lucas connectors off and use something like these. https://www.screwfix.com/p/ideal-lever-wire-connectors-combo-pack-30-piece-set/6472g Much more convenient and less hassle.
Welcome to the forum, I would suggest you check the wiring to the indicators on that side I think a lead or unit is shorting to earth. if you disconnect the supply to each indicator in turn you hopefully will locate the faulty one. It could be the supply feeding the rear through the chassis or at the trailer socket if fitted. Best of luck in finding it and let us know the result.
I don't think this would work if it parks at the top of the sweep and you reposition the arms to the bottom as the wiper starts to move it will try to pull the arms into the bonnet.
Welcome to the forum, When you say the fuel pump I assume you mean the fuel injection pump as you say you have replaced the lift pump. Stating the type of noise would be useful. Is it causing running issues? Is it a mechanical noise or fluid noise?
They have three pins to locate it to the boss so it will only go on one way. The locking tabs are opposite each other but they will only locate the tabs if the two sections can fit flat together.
You have some thing stopping the faces mating, screws are too thick or a plate. The Optimil boss is a great bit of kit especially with the anti-theft unit.
My order was delivered on Saturday morning from Tool Academy off ebay, I am impressed with the kit although I haven't tried it yet. As for the flanged rivnuts ideal in softer metals but leaves a gap between surfaces where as the other in steel or thicker aluminium reduces that gap. Unless of course you dimple it.