I'm not looking at mine, but I do have my 1986 factory wiring manual in
front of me...should just be two connections...  One with 2 or 3 wires
together on the same connector and a larger gauge single wire (purple).

Check to make sure the cables are providing the correct amount of juice
when the key is turned to the 'start' position.  I'd use alligator
clips on the leads of a multitester and then try to crank it and see if
the needle jumps up to 12vdc on the meter...

Also, just to be sure, I'd try to pull your ground source off the body
of the starter.

If you have long enough leads on the meter, you can set it on the hood
while it's open with the leads going under the gap between the hood and
body.  That way you can see the meter from the driver's seat and DIY
without having someone else start the truck while you're up front.

If you're not getting power at the starter wires, you'll need to start
tracing the problem down.  You may want to check the little junction
block on the firewall near the master cylinder.  Make sure the nut
holding the wires in place is properly tightened and that it's making a
good connection.

Let us know how it goes...

~jp