There are a number of problems with this design as it ages! I've attached a pic that shows some of what I found needed correction. I'll send a pic of the corrected version.
The red arrows shows a rivet that holds the spade lug connector and the bulb contact point. These seem to be 2 different metals- one for springing, the other is softer for contact. I've noticed high resistance in this riveted joint, loss of springiness, and poor spade lug connections on the wire and on the lamp housing.
The fix I followed was to drill out the mounting rivet, install new contacts points made out of available copper spade lug "double male" materials, re-rivet, solder the rivet to the assembly, and clean up the bulb side nib contacts (see yellow arrow) where the bulb seats in the lamp housing. Contact there was a real problem until the surfaces were cleaned with de-oxit, and the bulbs were forced against the housing with the increased pressure.
Pay attention to warnings on the board about increasing your wattage. Many a really nice lens assembly has been quickly burned-in using higher than specified.
I cleaned up the tragic soldering from the PO and the poor ground connection to the lamp housing and the body ground near the gas tank. The results from this work and a housing reflector re-silvering using aluminum foil "repair tape" was very surprising.
Good luck.