[fuzzypuppy]

I believe my settup is the same as what your planning.
I wanted as much off the starting battery as I could get, and put onto my secondary batt, stereo, aftermarket lighting, inverter, alarm, etc.
I completed mine several years ago and the paper sticker on my isolater is bleached now so I cant read the maker but it is the same brand sold in several auto parts stores, though since I had a higher output alt on my truck I had to call the manufactuer and track down one that would work with the higher amp's, best I can say is it is blue, and the reason I mention this is these people were great in helping me complete my setup, actually had tech's to talk to, in fact several times.
When you say the "distrubtion block" you mean the block on the firewall on the pass side, same as my 91 GMC 2500 correct?
this being the case there are 2 wires that will run out of the alt plug, the stock one that goes to the block and one that is supplied in the isolator kit, mine was yellow, and it goes to a different pole on the alt plug, right next to the stock one, this new wire on the alt plug goes to the isolator.
basicly your standard batt wires are left intact you just re'route them to one side of the isolator output, then run the new batt wires to the second isolator output, run the main charge cable from the alt out to the isolator input, the 4th smaller energizes the unit, the isolatot kit comes with a 30 amp stand alone relay for this pole. mine is mounted on the inner fenderwell next to the isolator.
I can't how important it is to get a good isolator kit, I started my project with cheaper parts and ended up with a leaking faulty isolator, dead batteries, and alot of headaches.
the system I have now has been in for 5 years and have never had a problem.
Sorry I cant be more specific as to exact routing because I have everything loomed tied and tucked.
the kit instructions were very good, the tech help I got was for sizing for demand and to explain the failure of the cheap system I first installed since I could not get a live person from that company to speak to me.
A good isolator will not only separate the batt's but the pole's are specific and will give the start batt, priority in charging as well as not over charge your batt's, my cheaper unit killed a brand new batt.
I did find my unit maufacturer on line, it's, surepower.com.
Not elaborate, the isolator and the 30 amp relay.
On another note, if your only pushing 9 volts at idle and your lights dim I'd say you have another problem, was this at your truck gauge? or from a multimeter at the alt?
lights dimming alot is an indicator of problems in the electrical system, connections, wiring going south etc. I had an old dodge that was like that,
For some pretty good diagrams, I punched isolator and duel battery install in google and tons popped up, lots of RV diagrams but it's pretty much the same.
I don't know what your powering but 200 amps is unreal power, I'm pushing 110 amps on a true deep cycle and the reg 850 cca battery, and have at times run my 2k watt inverter "thats under the hood as well" running 110v to the cab of my truck 110v back to a camper that i haul now and then, 12v to the camper 12v to a boat I'm hauling, tv dvd running in the camper, reefer running, camper lights, cell phones charging, 500 watt stereo going, at night with all the running lights going, etc, and I dont drain my batteries.
my alt is definately working pretty hard to keep it all going, but it does.
I set mine up after killing my battery running my camper in the boonies and not having enough power to start my truck the next day, long walk!!
now I can run the deep cycle way longer for the toys, and never have to worry about killing my start battery,
I wish you luck installing your settup,