Right on Edsut.
My power locks were behaving the same way. Bought the Haynes service manual for my "98 Venture" and using their wiring diagrams proved switches were OK. Was getting partial voltages to feed switches and was almost to go to the Dealer to buy a Body Control Module (BCM).
Stumbled across this Fantastic forum and the rest as they say is History. I took the ten minutes and lifted the "appeared to be dry" carpet to find it totally soaked underneath. Who knew it was lined with sponge foam. Several towels later I had that mess cleaned up and checked the wiring harness. It looked in like new condition but as I was looking at a huge bill for a BCM, I unwrapped the tape and found both the white and blue tri splice about 2/3rds of the way forward from the seat to the base of the firewall. I opened the "looking good duck tape splice protector" to find no connection. Only some green dust where the wire ends used to be. (Insert your own GM curse list here!) Once I sniped and skinned, soldered and sealed the wires back together the locks worked great.
Tip. I coated and let cure some silicon sealant or gasket maker on the solder joints, before electrial taping, to keep water out of the joints again.
Being curious I peeled back more tape moving forward and found two more splices. A large gauge (12) brown one was rotton but not broken yet,just due to it's size. Redid. Continued up about a foot past the "fork" and found a dark blue splice on the left branch but it was in great shape. Water did not get up that high. Moving aft I stripped back to the intersection at the passenger seat mount. Found another splice on a fine Black/White stripe wire (located right at this aft intersection) that was dissolved as well. I have no idea what this wire does as I cannot find it on any of my drawings but it is fixed now.
All this took about an hour in the driveway. Cost about 50 cents for the solder and some silicon and tape.
Thanks Edsut and GregA for all the great help.
This is my first post as I am New to this site. Sorry it's long. Just bought a "98 Venture, loaded. Type 4 BCM. It was cheap as alot of stuff was broken. In the last week I fixed Power locks, power windows, drivers power seat, wipers parking vertical and reprogramed the BCM to get the anti theft working and reactivated the theft lock radio. All from the helpful info at this site. Saved a fortune, I'm sure. Thanks again All.