I was having the same problem on my 88 yesterday. Blower would randomly come on when I hit a bump while driving. I found the connector was loose at the fuse block where the fuse plugs in. I removed the fuse block, one bolt under hood at firewall, two Phillips head screws interior fire wall. From rear of fuse block, removed wires for blower motor and tightened female connectors with pliers. Put back together and works flawlessly. Hope this helps.