I wish I hadn't sold my 98 Helms manuals, those things were badass, very detailed.
I guess the first place to start is to find the door schematics (if there's such a thing) and let's find the wire that powers the door soleniod, on that soleniod there will be probably three wires (maybe more gm likes to over do it and be safe, heheh) lets find the signal wire coming from who knows where and connect those two from each door togother, jeez if that made sense.
i'll search around for the schematic too, maybe gmcwantsls1 will chime in, i think he has a cd that may have some info on it, if i remember correctly.
allen