Ah BryanP,
Yo from the coast of our fine state.
I too purchased a Rabbit in Roseburg in 2010 and then proceeded to make it the car I needed for the 4.5 hr trip at times from Portland to the coast where I had wife and home. Portland was the work spot and the commute necessitated a vehicle with mileage. When diesel went up to around 4 bills a gallon I started running it on filtered waste veg oil. So a bit of an investment there that I bet I never recovered.
A couple years ago, after retiring I stumbled on an 81 Pickup that needed project finishing. Some day IF I will stop using as a daily driver and workhorse I will get it painted and all done. I don't get the 40-50 mpg out of it but that is due to two things, the turbo and tuning it. Once you get that extra HP under foot it is hard to not use it. I still get near 30 in town and really don't do the long hauls anymore so maybe I would approach the higher MPG if I continued to drive I 5.
So yeah welcome to the forum. On to the questions. Wiring is bad, possible relay problems, GP unsure of and a host of head scratchers.
Ignition switch failed? If the dash lights like oil and brake and charge lights come on then at least those wires are getting the voltage they need. I bought a new ignition switch here a bit back and came to find that the contacts were kind of weak and with the starter and GPs pulling a heavy draw initially the switch contacts became bad due to arcing. So I went with a separate relay for the starter and took the load of that off the switch. I put a relay on my Rabbit for the GP's but have not done the same for the pickup. Not sure why.
I don't think there is a relay for the fuel solenoid. Just power off the back of the ignition. So having the manual over ride is really just a cheap anti-theft device. Leave it as is. No one will be able to figure it out.
No indication of GP action? You have a meter for 12 vdc don't you? Tag that buss bar and see if you are getting some voltage of some sort. If not, look on the firewall, big red wire from buss bar to small box. It should have a small strip of tin across the two screws. You can even make a couple of these and keep one in the glove box. Or? You can simply replace that fuse with a more modern one in a nice weather tight holder. I use a fuse from the sound system folks, a nice 40 amp one. Those are easier to buy than to make one from a piece of roofing tin. But I did that too.
Ok, if you can crank the starter but it doesn't start I have to ask is that by using the key? Or a jumper cable from the battery to the starter. Ignition switch seems fine if you are using the key.
Cranks but does not start. Oh man how many threads start with that line?
Without GPs you won't likely get it to start unless you are located in the hot side of the state in July. You need to verify you have good plugs and to do that you need to take them out an test them.
DO NOT hold on to them and touch a wire to the battery and ground. Unless you don't want to do anything with your fingers for awhile. Put them in a pair of vice grips and then hot wire them. If they don't glow red hot replace them. If they are not smooth and have a nice rounded tip, replace them. I think between GPs and air in the fuel lines that accounts for 95 percent of the no start diesels.
Draining the fuel and making it fresh is a good idea. The IP acts like a big pump that sucks the fuel from the tank and spits it back in over and over again. Way more fuel goes through it than is used by the injectors. It is meant to cool the pump and it also will need attention.
Fuel filter might need to be replaced at the same time the fuel swap. If it has bad juu juu in it that will go to the pump or keep the pump from sucking fuel in.
I think you may know that the fastest way to determine a fuel problem is to eliminate most of it temporarily. Get a nice stable quart or half gallon container and take the fuel line off the filter and stick it in there. Then do the same for the line coming off the back of the pump. If you can't get the pump to cycle fuel in that manner you may have a bad vane pump or a blocked line. Lines clear with pressure or vacuum but the 4 little pieces of metal that make up the vanes on the inside of the IP will require you to A. take the pump apart and free them up. or B. soak it in ATF or diesel purge and hope that breaks them free.
Addressing the hack job wiring is second to addressing the fuse box connections. Sometimes these cars leak down water into that part and all the contacts become corroded or bad and pulling that fuse box down and giving it and the wires that go to the body of the car for a ground a good brushing will help in a lot of ways.
As to wiring I would pull all the fuses and relays and only put in the ones needed to get it running. The GP relay is wrapped up on to the box and not actually in there. Pull everything out and get back to them after you get it going. fuses are cheap and you can use a meter to test for a short prior to inserting one if you wish. I would pull new wires and clean contacts before trying to do a different loom. Chances are the hours you will spend chasing electrical gremlins is going to be huge. But doing a new loom is not quick either.
Source out parts yards and online sites for relays. You near Portland or Salem? They have a good number of Rabbits and you may find what you want for the entry fee you are going to pay them.
The pickup is just a Rabbit from the front bumper to that back window. So parts will work from a four door Rabbit on the pickup. Two door is longer so beware. Yes I know the truck is a two door but a short door compared to a Rabbit two door. Trust me I own a two door Rabbit.
Keep us posted, sorry for the winded reply. Just a good day to do forums as the rain keeps me off the streets.
Enjoy.