I have a metal edging on my roof in an area about 4 wide. Can I run heating coils over this metal section of the roof,because it seems to be an area that has ice dams. Presently I have a coil above the metal area, but thought that was the only possible venue.
You mean you have heating coils further up the roof - toward the peak - from the metal? That's not a good idea, since it melts the snow from the bottom up, and the water from that melting runs down onto the metal & freezes there (that's the coldest part of your roof, because the overhang isn't heated by the house's interior). The result is ice damming.
It's also not a very good idea to add heating coils on top of the metal. If for some reason they happen to not function (say a power outage or a switch failure), they'll get torn off by the sliding snow/ice. A better idea is to heat from inside the soffit, allowing that heat to rise through the metal roof.
If that's aluminum, you really should coat it with something; aluminum is hydrophilic, meaning water likes to cling to it either as water or as ice. I'd love to see you replace it with copper, which isn't nearly so hydrophilic.