My 89 should be similar to your's and I'm in the process of cleaning things up. You are aware that that big ol' can mounted at the pass. side top firewall is the servo unit, right? (its the one with the cable to the throttle body). There's a harness that comes from the dash, through the firewall that has a vacuum line, a multi-pin connector, and a single pin connector (looks sorta like an in-line fuse). The multi-pin connector plugs into the servo, the single pin connector plugs into the passenger side harness from the firewall. the vacuum line plugs into one of the ports on the servo (not in front of me now, so hard to remeber which one). Under the dash, coming from the column, there's what APPEARS to be a signle wire with an odd looking connector about the size of a Chicklett. It has approx. 5 contacts on it and plugs into the yellow cruise control box if I recall correctly (about to do that so I'm going by memory when I pulled th column a month ago).
Search for cruise control writeups.
Are you adding or fixing a cruise control?