Dual tank wiring 70's vs. 80's + Updating wiring?

[hrc200x]

I tore apart my '75 chevy today. The wiring outside the cab has a large harness that runs to the starter, out of that harness comes a wire that runs down the passenger side frame rail to a plug in, then to the dual tank switch I belive (I think this wire is for the Fuel Gauge for each tank?) Back up to the firewall: There was a 4 pronged plug in right at the fire wall, the wires from there goes down the driver side frame rail, accross a crossmember to the dual tank switch.

My plan is to use either Blazer or Suburban wiring harness for under the dash wiring. I'll probably end up using the Blazer/Burban wiring outside the cab because I want delay wipers and headlight dimmer switch on the column. I would use the '75 outside of cab wiring, but because the wires for the wiper motors are part of the main harness I don't think I have a choice but to use newer outside of cab wiring. Since the blazer/burban only have a single tank will this still work?

I looked on my dads '86 Silverado with dual tanks and he has no wires down the passenger side frame rail.

Is there any wiring diagrams on the net for pickups/Blazers/suburbans?