OK.. for the next guy who comes along:
- I have found 4 modules made by Impart. Central Locking (CL) and GMC Engine Monitor (EM) behind the glove box. Combi Flasher (CF) and Reserve Battery Controller (RBC) in the box added behind the passenger battery.
- There was originally a third battery between the passenger battery and the firewall. That was gone.
- There is a block heater. Mine just has the wiring in a junction box on the firewall with the plug already gone.
- There must have been quite a few sets of lights on the front of the ambulance.
- There was something on the outside of the fenders at the front. There are holes that have been welded shut and the wires still go through the inside of the fenders just behind the radiator support. I just cut those out.
- There was some kind of control panel inside the truck that accounted for the majority of the wires going through the firewall.
- I believe the EM just lit up some lights on the control panel or something. Disconnecting it has no ill effect that I've found so far.
- My central locking doesn't work (even the door switches), so disconnecting CL seems to do nothing bad.
- I found all of the control panel wiring wrapped back up the loom going from firewall to CL. That made it look like many wires were going there. They weren't, they were almost all already chopped.
- After feeding all of the control panel wires back through the firewall and cutting them out of the firewall to RBC/CF area, there are about 4 wires left going from RBC to firewall then up into the dash. I suspect one is ignition switched. I don't yet know what the others were for, but I have disconnected RBC and CF and haven't noticed any issues yet so I will likely cut them even if I can't trace them to their destination. I think that means the whole loom going from CF and RBC through the firewall can be cut out.
- They put two headlight relays on the radiator support next to the passenger battery (great!). These are powered by a thick purple/pink wire coming from the Fuse/Relay Centre.
- The stock headlight harness is still running along the bottom of the front of the radiator support. The brown, tan and green wires that originally powered the parking, low and high beams are still functional.
- It looks like the stock passenger headlight connector was cut off and replaced with a connector to send these wires to the relays.
- In front of the passenger side of the radiator support, stock low beam (tan) goes to white/blue to low beam relay. Another white/blue goes up into the ambulance stuff, to a loose single connector. No idea. Low beam relay then powers white/purple to both low beams. So even with all of the ambulance stuff cut off, the low beams work.
- Stock high beam goes to purple/white to high beam relay. The relay sends 12V up the two pink wires into the CF. The CF sends high beam power through grey to the passenger high beam and blue to the driver high beam. This is so it can alternately flash them when the lights and sirens are on. With the CF disconnected from power, the high beams will not work. Cut one pink and connect to blue, cut the other pink and connect to grey. High beams now work.
- I am not sure how the ambulance stuff actually energised the high beam relay without the driver having to turn the high beams on. I was expecting to see a wire from CF to purple/white. This has me puzzled.
- There are ground wires for EVERYTHING. There is a large ground wire connecting to the radiator support behind the passenger battery. It connects to a bunch of black wires in front of the radiator support. They are connected again in front of the radiator. All of these can be cut out except the one for each high and low beam.
- There were orange/black and yellow wires for more pairs of lights. The lights were gone, so I removed all of those wires too.
- There are a bunch of heavy gauge wires coming out of the relays on the ambulance block. I think they went to the medical module.
- There was an extra fuse panel on the firewall with five 100A fuses. Not sure what they were for.
- The passenger alternator seems to have had some control wires going to the control panel or the RBC. Its output stud was connected to the Fuse/Relay Center.
I have removed a couple of shopping bags of wiring and relays and "stuff". I haven't decided what I will do with the third battery tray or the second alternator. Likely I will see if two alternators play well together. If not, I might keep it connected up but just have switches on the two field windings to have a spare alternator ready to switch to if needed.
The two batteries will be replaced and all of the battery wiring has been pulled out. Previously it seemed to be starting off one battery, and was killing batteries doing that. I will go back to almost the stock arrangement. I've run a 2awg cable from each battery + to the starter, and a 2awg from each battery - to the block. I will likely run another 2awg between the two batteries' +. When I change to the petrol motor, I'd like to give a lithium battery and supercapacitors a go. I'm not totally sure how they'd go with a big winch though. I guess I need to measure the current draw when using it first.
If I end up running on one alternator, I will upgrade the alternator/battery wire that was there. When I put the winch on, a single alternator could be putting out near 100A and that wire would melt the fusible link. I'll add a 100-120A circuit breaker. If I use both alternators, probably one wire to each battery with 100A breakers.
