Speed Twin Wiring

As factory shop manuals aren't available, I've ordered the Haynes manual that covers the 1200cc twins. As this includes the Thruxton, I assume there will be sufficient information that pertains to the Speed Twin. In the meantime, I'd like to ask a question concerning the availability of a switched hot lead for accessories.

I'm installing a Garmin GPS, which will require a switched 12v lead. Is there a dedicated accessory lead somewhere in the wiring harness (perhaps the power source for the optional heated grips?) If not, can anyone tell me the color coding for the tail light wire, or perhaps the headlight lead? Is there a 12v wire "upstream" of the 5v USB port under the seat?

I thought it would be worth asking, before I start probing with a voltmeter

 

Thanks for the responses. I've ordered the Haynes manual, which came with a short term free subscription to the electronic version. I'll probably check the on-line wiring diagram while I wait for the hard copy. I have powerlet receptacles (similar to the Triumph accessory socket) on a couple of the bikes for connecting the Battery Tender and heated gear; these are un-switched. I'm going to use switched power to the GPS so I don't have to remember to turn it off each time I stop the bike. I'll check the current draw for the GPS; it's probably low enough that I can wire it without a relay. When relays are need, I've had good luck with miniature relays from Eastern Beaver. I'm hoping that there's room under one of the side covers for the GPS power box.

 

I checked the 12v wiring between the main harness and the USB port, and found that it was switched. I tapped into the white "hot" lead to the USB for the positive power to the GPS power module, and attached the the negative GPS lead to the negative post of the battery. Everything was easy to access. There is room to attach the GPS power module to the plastic shield behind relays under the right side cover, with everything being covered by the bodywork. I'll remove the fuel tank and route the lead to the GPS along the wiring harness that goes to the front of the bike. It doesn't look like the lead is long enough to reach the GPS mount, so I'll splice an extension in under the tank. I'm using shielded spade connectors on the GPS power lead where it comes down from the clutch perch mount, so that I can remove the GPS cradle if desired. Heat shrink tubing will cover these connections, to clean things up a bit and add a bit more waterproofing. (I used a similar set-up on my XR1200 Harley, and it's stood up to some toad strangling rainstorms.)

I don't anticipate taking the Speed Twin on long trips, but having the GPS available when I've hauled the bike to more distant locations will help me get back to the motel after I've wandered around in unfamiliar territory (and find the nearest gas when I get close to 150 miles on a tank.)