When I wired my Motolights I took switched power for the control relay from the diagnostic plug. This worked, but meant that the lights came on as soon as the ignition was switched on (assuming the Motolight control switch was on – almost always the case on my bike). That equates to a draw of 100 watts (about 8 amps) from the battery during the startup ritual before hitting the starter. This usually doesn’t hurt, but suppose the battery battery wasn’t fully charged some cold morning. That 8 amp draw could be the difference between starting the bike and looking for a jump.
So far I’ve avoided the need for a jump by trying to remember to turn off the aux lights before switching on the ignition on cold mornings. Not wanting to trust my (bad) memory forever, I finally decided to change the wiring to take switched power for the Motolight control relay from the headlight main beam. Since the headlight doesn’t come on until after the bike is started using it as a control signal means the Motolights won’t come on until the bike is started, too.
When I removed the Motolights in 11/2008 I kept this wiring to control the relay on the Hella Micro DE Fog Lights that replaced the Motolights. Then, when I added a Fuzeblock three months later I used this wiring to trigger the Fuzeblock built in relay.
Headlight module connector
This pictures shows the plug that provided power to the headlight bucket. I pulled back the rubber rain boot to take a look. The yellow wire is what I need to tap in to for the control relay. The problem is that I can’t see how to do this without making permanent changes to the plug, cutting the plug wiring, or negating the waterproof qualities of the rubber boot. I need another way to get to that yellow wire. I put the boot back over the connector and plugged the connector into its socket.
Feed wire through breather
There are several hollow rubber L shaped tubes coming out of the headlight housing with the end of the L pointing down. I suspect they are there to vent the housing. The bottom of each breather (if that is what it is) resides just above a flat baffle molded into the plastic housing. My guess is that is to keep water from splashing up the vent. I fed some wire through the breather to the right of the main beam access port.
Ready to connect
Connected and cable tied
I pulled enough wire through the breather to give me some slack and then stripped of the end and wrapped it around the connector for the yellow wire. No crimp, no solder. This may not last, in which case I’ll try a more permanent connection method, later. For now I used a cable tie to provide stress relief. The advantage of doing it this way is that I can remove the lead and bring the bike back to 100% stock without any lasting changes to the bike.
Relay/switch junction
I routed the control lead under the tank and into the space under the tool tray with the Motolight fuse and relay. A female quick disconnect was put on the control lead so it wont short the headlight should it come apart. A mail connector was added to the lead that goes to the Motolight switch. When the switch is on any power on the control lead will be applied to the primary of the Motolight control relay, turning on the secondary which switches fused power directly from the battery to the lights.
I put the tank back on the bike, switched on the ignition, and waited for the power on test to finish. No headlamp faults. No Motolights. Good. I then started the bike. The Motolights came on with the main beam. Great! I like this much better than having to trust my memory.
Update
It’s been almost 4 years and my temporary connection is still working just fine. I did make one modification: a connector was added to the control lead as it exits the vent tube. The added connector lets me remove the headlight buckket/instrument pannel. I needed to do that to repair a broken bulb retaining bail in 2009.