Taillight Voltage on 2012 R1200RT

[azokie]

2012 R1200RT. I removd the taillight housing with the idea of using a taillight wire (positive side) to trigger a relay. With the ignition on, I measured the voltage at the actual taillight and the reading was around 2.9 volts. Yet, the taillight are rated and use a 12v bulb. I started the bike and got the same results.

What's going on with the 2.9 volts verses 12 volts?

 

Is the 2.9 volts enougth to trigger a relay?

[Boffin]

The bulb is a 12V 21Watt lamp.

In simple terms, if it is fed with a lower voltage it glows less brightly for use as a tail-light. Apply the brake and the voltage goes to 12V and the lamp goes to full brightness for the brake light. In fact, most of these systems use pulse-width modulation of the full voltage, but your DMM will smooth that out to the indicated 2.9V.

This however, limits the usefulness of the tail-light line as a relay trigger, except to power aux brake-lights.

 

Andy

[azokie]

Thanks andy. Makes sense. I will look for another 12 volt source for a trigger. Any thoughts? I am lookinjg for a source that is not time delayed by the Cambus like the GPS connector up front under the steering head.

[Danny caddyshack Noonan]

I'm using the front parking lamp. I've got three coming off of the 6 lead connector going to the lamp assembly. I didn't have use for it until I picked up a Centech yesterday.

I've got LED lamps on the high beam and am hooking up fog/conspicuity lamps coming off of one of the low beam lamps today.

 

You can get really good access without removing plastic. Pull the connector out to the right side and do your work. I used to use the line taps but now just strip about 1/2" of insulation and solder a wire right to it to avoid voltage drops. Wrap with really good insulation and move on.

[dirtrider]

Afternoon azokie

 

If all you want to do is trigger a relay at ignition switch ON then try the green wire going into the diagnostic connector (large round cap covered connecter under seat) or the yellow black wire going to the starter relay (again under seat near the diagnostic connector).

 

Or- use one of the front running light circuits (small bulbs on either side in the front). To see what & when you get there just turn the key on (don't start engine).

 

It sounds like your meter didn't get a good measurement on the tail light circuit, as Andy said, it is pulse width modulated but the pulsed voltage should be closer to the 6-8 volt range.

You still can't reliably run a relay off of that circuit as the pulsed voltage will make the relay buzz.

 

[azokie]

Thanks all. I did a posilock splice on the right running light (parking light)positive wire (grey) for a relay trigger. The hardest part was getting the parking light back into the socket and locked in. There is so little space to work but I finally got it locked in. I did remove the right turn signal housing. Otherwise, I do not see how one can access the small bulb.