here we go: if you just check the gauge on the wiring that goes to the housing of the bulb, you will be able to look up the max current rating for that gauge of wire here:
http://www.powerstream.com/Wire_Size.htm
you figure average current going to a 35w HID would be 35w/12v = ~2.9amps, so average current to a 55w HID would be 55w/12v = ~4.6amps. make sure to use the "chassis wiring" numbers when figuring out what your wire can handle.
i'm pretty sure that we can at least access the connecting wire without going through too much trouble, so a simple look under the hood should tell you what we have.