90 plus percent of electrical issues are the result of poor negative/earth connections.
Love to help you out Matt but the tyranny of distance and all the restrictions make that a bit difficult. You just need to get motivated and get those wire cutters snip, snip snipping! Disconnect the earth wire fist though !@Rusty Panels , the wiring in my old Disco is a dogs breakfast after years of dodgy work done by multiple people, sadly including me, feel like dropping over for a BBQ and a afternoon or two of fixing, I just couldn’t be bothered after spending all week installing cabling and equipment