Sounds like the ground strap to the engine/transmission is not connected. The engine and transmission are mounted to the frame in three places using rubber mounts to isolate the engine/trans from the chassis and this type of mount also isolates the engine/trans in the electrical circuit requiring a connection from the engine/trans to the chassis. There is a separate ground strap (large diameter wire with fittings on the ends to allow a bolt through). The ground strap must be connected to the chassis and engine/trans to ground them so the electrical current can complete the circuit.

Good Luck!
Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.