"Jeff" wrote in message news
I inspected the electrical system and found that fuse on the negative
lead had blown. Why manufacturers persist in providing a negative
wire fuse will remain a mystery as there are very few positive ground
vehicles still in service and even marine radios with floating grounds
are scarce. I have no idea where the radio was getting its ground
return for reasons that will soon be obvious. I replaced the fuse and
continued looking for problems.
The negative fuse is nothing to do with positive ground vehicles (and a
radio with the case connected to negative would not work in a positive
ground vehicle anyway without additional isolation).
I wired up a neg ground rev counter to my pos earth 1963 mini in 1969 by
insulating the live case of the rev counter and earthing the live
terminal...worked well .....