91 Classic No Start

[dschwartz]

I've been battling with my '91 Classic for a few weeks, am stumped and would appreciate any suggestions:

Initial Problem/Symptoms: Pulled truck into garage and shut down. Few hours later, went to start and would not start. No attempt to turn-over, no click, no tick-tick-tick - nothing. Put trickle charger on battery - few hours later charger showed errors. Reset charger and put on trickle overnight and awoke to same errors. Took battery (6+ year old Optima) to local auto store for test and it failed. Bought new battery, charged overnight, and same no-start.
Could not hear any engagement from the starter, tapped a few times with hammer while key turned - nothing. Removed the starter (two-week process with stuck bolts - another story) and took to store to get tested. Failed test several times so I got a new starter (and starter relay) from AB and just finished installing. No start. No click, nothing.

One thing I have noticed, is that the Onboard Diagnostics Display (under right-side seat on '91 Classic) flashed a dim 88 and then is blank. will not flash anything until key is removed and 5 second wait for ECU to drop out. Correct me if I'm wrong, but won't the diagnostics display show codes with key turned on, even without engine running?

I check as the relays under the dash and under the seat and all seemed seated firmly. I also cleaned all the battery cables and terminal ends at the starter, including the ground strap mount before installing new starter.

I'm at a loss here - and facing have to have it towed somewhere unless someone has any ideas/suggestions for me to check? Any help would be greatly appreciated!