Welcome to the wonderful world of ambulance conversions!
I see several problems right from the start, and they are all due to weight. As Pat mentioned, his trailer will probably run about 6000 Lbs, which makes for a heavy trailer. The tow vehicle will need to be able to move this, both at high way speeds, and off the road.
MNtal is rebuilding a Freightliner/Horton medium ambulance so he can tow his off-road vehicles, which means a 10,000 Lb trailer. His Freightliner has a Cummins 8.3 engine, and he has told me that he's planning to add a pyrometer and get it tuned for more HP. Food for thought.
In my opinion, the best approach would be for you to make the tow vehicle and the trailer as independent vehicles - each can live without the other. This means 2 solar systems, 2 water systems, 2 battery systems, etc. Otherwise, one equipment failure could stop things cold.
If your first build is the ambulance itself, then you can get it out on the road while the trailer build is in-process.
Lighting? Worry about the fixtures that you will use daily, such as the ceiling lights. I installed Tecniq ambulance ceiling lights in my module, and cut my ceiling light amp load from 30 amps down to 7 amps. Since these lights will be the primary lights I'll use, the expenditure was well worth it. On the other hand, the lighting in my compartments is via incandescent rope lights. Very inefficient, but since they only come on when the cabinet door is open, plus they don't draw a lot of power, they will stay there for as long as they are operable.
Virtually every ambulance comes with a Vanner inverter/charger. It does what it does well, but I disconnected the charger portion of the Vanner since it is a 3-stage charger. I went with a high quality charger with 4-stages: every 7 days, it does an equalizing charge.
Blue Sea electrical components are about as good as you can find - I found the best price on Amazon (figure out the part number of what you want through the Blue Sea catalog, then do an Amazon search for that number) - right about 40% off list price.
Wire should be rated for the use you plan. Del-City has 100 ft rolls available of under-hood rated (Type GXL, for instance) wire, but I use marine stranded wire inside the module. You will find that ambulance builders generally use commercial SO rubber power cable for 120 volt runs. Never try to connect SO cable with wire nuts - the fine strands result in a connection that is very poor, and the wire nut can usually be pulled off after a while with 2 fingers. Only use either crimp or solder terminals for all your wire terminations - you'll primarily need 14-10 gauge. When you crimp, use a ratchet crimper instead of a pliers type. When I terminate SO cable, I look at the copper, and if it needs cleaning, I like to use a wire wheel so the inner strands get cleaned as well as the outer strands.
Don't be in a hurry to yank things out, and don't be in a rush to throw away what you do remove. Ambulance parts are 90% off the shelf, but the shelf can run into money. Save any used bulbs - new ones, especially for Whelen emergency lighting, can run more than $20 per each (at that point, a used bulb is just fine with me). If your compartment door locks are cranky, they can be easily cleaned, and new Fort cores bought from someone like
www.selecttechambulance.com.
Also, periodically check the Foster Coach (
www.fostercoach.com) site for surplus components - that's where I've found a lot of what I need at a nice discount.
It's too bad that we all can't sit down at a table with a pile of donuts and lots of coffee every week or so, isn't it?
Have fun, and you're always welcome to ask questions an offer suggestions.
Ciao -
credit where credit is due. modifed from patoz's 0.5 ambo build.
