94 Silverado with 4.3TBI-5.7TBI swap and a 4L60

Short version.....Am I able to set my base timing by jumping the A and B terminals in the diagnostic port?

Longer version.....I picked this truck up, it was priced decent since it ran like dog poo.The timing was way off, the owner thought the motor was coming unglued.It made the drive home, but was severly underpowered and had a very irratic idle.I got it back into town and stopped by work, and reset the timing by ear, i was lacking a timing light.It picked up a good amount of power, but still has the lopey idle when letting off the gas, but will pick it self back up to a smooth but high idle.This truck was a 4.3TBI truck, and was swapped very poorly.Lots of stuff unhooked, some wires are cut, but the truck gets me to work and back.I searched for the Tan/Black wire to unhook to set the base timing.I found one that looks to be the right one, under the dash near the blower motor.The truck doesnt respond when i unhook it, so im failing at setting the timing.I plan on ripping this truck apart little by little and cleaning it up, but i want to get the timing set.Its running very rich, and still seems sluggish, with the irractic idle.I read somewhere, the timing can be set if the A and B terminals are jumped in the diagnostic port.This would put the truck into bypass mode, as though i were pulling codes.Is this accurate?


BTW, I really like this truck...id love to find somebody that would be willing to take a look at this thing, and let me know the best route in cleaning the wiring up.Im not even sure what im looking at, but id bring some beer for a teaching session