[Spridgets] halogen

[derf]

Oh, no, not common ground.
A 55W bulb is a 55W bulb.  At 12 volts, that is 4.6 Amps current, per.
 9.6Amps isn't a problem for good wiring in the 14-16 gauge range, for
short
runs in a Spridget.  But, 40 year old wiring can be deteriorated and have
higher resistance to current flow.  A relay effectively shortens the run of
the high current carrying wires to just a few feet.
Halogen bulbs have better light output at the same wattage as regular sealed
beams.