Thought I'd update this for anyone installing an in-shell headlight relay from Eastern Beaver or elsewhere on a K75 standard or any K bike with the round headlight can.
Unless you do the permanent install you will have to run the new relay wiring out of the headlight can. The existing grommet only will accommodate the OEM wiring. You can create a new grommet that will accommodate both the new and the old wiring using rubber leg tips from any big box store for under 3 dollars and about 5 minutes.

Drill a hole in the top then of the new 'grommet' to expand the hole with exacto knife till big enough to accommodate both old and new wires. Slice it from top to bottom and fit the wiring into the middle. Stuff the new grommet into the hole so it is snug. Mark the line where edge the of the hole meets the grommet. Remove the grommet from the hole and cut a groove along that line so the edge of the hole fits within the groove. Lay the wiring back in the grommet, stuff it back in the hole so the edge of the hole rests in the groove. Touch up with silicone sealant -- grommet should work just as well as the OEM one.