Menu Close

Headlight Relay Installation on K12RS

K1200RS Headlight Relay Installation

by Ed Benson
June 2001

In the quest for more light, I recently ordered a PIAA Super-White 85W for my high beam, and a Solara 100W H7 Xenon bulb for my low beam. Pirate (Jerry Finley) has this set-up and swears by it.

While Pirate just plugged his in, several on this list and elsewhere expressed grave concerns about the increased wattage (from 110 to 185) causing fried wiring harnesses and melted headlights. Greg Girard has personal knowledge of this, but not specifically on K12’s. Our bikes are probably over-engineered to handle add’l loads, but the “probably” bothered me.

I’m lucky to be in possession of a spare headlight assembly, so a melting headlight is an acceptable risk (as long as it doesn’t catch fire (!)). But I REALLY don’t want to melt my wiring harness – a repair would be both expensive and time-consuming (apparently Brian Curry has experience there, again, not K12-specific).

In any event, I did my research, esp. the Tech Articles posted by Don Eilenberger and Brian Curry. The set-up for the K12 is a little different, but actually simpler since the K1200RS has two separate bulbs.

It took the better part of 3 days and a LOT of trips to Radio Shack, NAPA and Discount Auto, but the project is complete. I now have at least 12 ga wire running all the way from the battery via the relay to the bulbs (with the exception of about 1″ from the plug and the wiring inside the headlight – which looks pretty substantial). The stock wiring to the plug does seem awfully small by comparison. The case of the relay needs to be grounded – I used a battery-starter cable from Discount Auto as a ground lead – it runs underneath to the post in the photo to the frame, and grounds the case, the wiring harness, and provides a convenient ground for future projects (front running lights? Moto-Lights?). Switched and unswitched 12V is also now handy.

For the wiring harness, I was lucky to have my “parts” bike to get an extra headlight plug from – it’s come in really handy.

In the interest of backwards-compatibility, I tapped into the headlight circuit up-stream of the stock headlight plug. If something goes wrong, I have 2 failure modes:

  1. If the relay fails I’ll carry 2 switched jumpers in my toolkit
  2. If I need to revert to stock, I can switch back to the stock bulbs (carried as spares), unplug my wiring harness and plug in the stock plug (seen to the left in the photo)

The lights SEEM much brighter than stock, but I’m looking for a stock K12 to do some side-by-side photos at night for comparison. The headlight does get hot; I’m wondering if Pirate’s Scoop kit could be modified to direct air into the headlight assembly.

Thanks again to my gurus, Brian & Don. Shoulders of giants and all that…

Leave a Reply