One area to check is the wiring under the wing. It is a VERY exposed area. Spray from the wheels when driving in the wet coats everything. Morgan used bullet connectors to connect the wiring and these are poor for keeping water out so you get corrosion in them. Mine (2002car) were solid, couldn’t split them when checking for a similar problem to yours. I cut the wires and rejoined with spade connectors, finally sealed the joints with shrink wrap. That cured the problem for me.
Gomog website has wiring diagrams but they are a guide only! Morgan had a habit of changing things so the wire colour codes could be different!
www.gomog.com
