Yep Rog is spot on there! If you are getting a leak to earth via the fluid the rad will become the sacrificial element or rather a sacrificial element. This is something that became very relevant with the advent of silicone hoses which totally isolated the rad, couple that with a rubber gasket to the top support bar on a Morgan and you have just successfully isolated your rad from ground.

If we are now specifically talking Morgan with an after market alloy rad then using the top or side mount brackets drill a small hole in a suitable place and connect an earth wire with a terminal loop and run the wire to a confirmed earth, as close as you can to the origin of your wire this will provide a better earth solution than the coolant. As Rog also stated the older the coolant gets the more likely that it is to hold a current, couple that with micro metal elements carried in the coolant and disaster awaits the uninformed.
Just change your coolant every two of three years and do a proper flush at five or six years as when you just drain the system passively some of those metal elements will remain in the water ways. Oh! and make sure you use the recommended grade of coolant for your car or a suitably listed improved option. Herein lies another complete subject!