I have the Manuals for my 94 Marquis (93 Build date), however the engine is a 8.3 Cummins Mech..    The manuals do not include electrical schematics.  For the electrical I use this pdf  "Beaver Service Manual (Electrical Diagrams)" found on the BAC Site.  It's from a late 80's Beaver I think, not perfect though useful.   The Beaver Manuals (not the chassis/engine) are nice to have, but have not been that useful when chasing problems.