Tail light question - 2 wires vs. 3 wires

Call Of Doodie

Been Around the Block
OK, so it's going to be pretty clear that I'm no electrician here:
I just got a new tail light that I like better than the dinky one originally mounted at the bike's cafe transformation, and I just realized that the new one only has two wires, while the first one has three: one for tail light, one for brake, one for ground.
Do I just splice the tail- and brake- lights together, or what do I do here?
Please be gentle, and explain like you're talking to a 5 year old - ;D
 

Sonreir

Oregon
DTT SUPPORTER
Chances are, the new tail light needs to be grounded through the mounting bolts. I suspect that one wire is for running lights and the other wires is for the brake lights.
 

Call Of Doodie

Been Around the Block
Hmmm...OK, thanks. Even though the wires on the new light are black and red? (I always thought black was ground?)
Next stupid question: how does one figure which wire goes to which? Will it hurt anything if I try wiring them and hook them up wrong?
 

1chrisb

Been Around the Block
Touch the base to the negative post on the battery, and the red wire first to the positive post. If it lights up, then touch the black wire to the positive post. One should be brighter than the other; that's the brake light. If the red wire doesn't make it light up, then put the black wire to the negative post, and the red to positive. That should hopefully tell you what you need to know about how it needs to be hooked up. It's only 12V, so don't worry about getting shocked, you can just use your hands to touch the wires to the posts.

Sent from my SAMSUNG-SGH-I717 using Tapatalk 2
 

Call Of Doodie

Been Around the Block
Hot damn - worked like a charm.
Thanks for guiding the electrical noob through what I'm sure is pretty basic stuff to most of you.
All that's left now is picking up a nice big hole saw so I can mount that puppy now!
 

Call Of Doodie

Been Around the Block
LOL - glad to hear that. :-[
I'm pretty embarrassed that after all these years (and the refurbishing of several old Mustangs and T-birds), that I still know relatively little about, well, just about anything electrical - outside of pretty straightforward aftermarket installations of things like lights and switches, stereos, etc.
 

AgentX

Over 1,000 Posts
To my credit, the "mechanic" (I'm in India so I use the term loosely; the man has inspired me to do 100% of my OWN maintenance from now on) who mounted the tail light seems to have thought the red wire was the ground, too. Or maybe he just wrapped the wire on the frame and tied (?) it there with electrical tape for some other reason. But I was partly going off his work in my assumption.

I ordered a 3-wire light before I'd realized the truth, too. Oh, well, at least I have a backup now.
 

Call Of Doodie

Been Around the Block
Well, since I've had a couple of people message me about how to do this, I'm going to post up what I hope are clearer instructions on how to do this swap. It's really just a summation of what everybody told me to do here, so credit goes to all of you guys that helped out:

Although it seems like most aftermarket tails have just two wires, one black, one red...I believe every bike will have different colours for their wiring that you have to connect to. But basically what you should end up with from the BIKE are: 1 wire from the headlight (which will go to the "running light" or the dimmer of the two lights in your tail light), 1 wire from the brake light (which will go to the...yes, brake light or the brighter of the two lights in the tail light), and the ground wire. Since you'll be one wire short (no pun intended) from your tail light, attach a piece of insulated wire to something metal on your tail light where ever you can make a good, solid connection (you might have to drill a small hole in the base, then screw the wire to it, something like that - just remember that you have to leave yourself a way to run that new wire from the tail light through your seat cowl to the bike's wiring), then attach that to the ground wire from the bike, and you're in business.
If you need to figure out which wire is which, or check to see if everything is working the way it's supposed to, just touch your new ground wire to the negative post on the battery, and the red wire first to the positive post. If it lights up, then touch the black wire to the positive post. One should be brighter than the other; that's the brake light. If the red wire doesn't make it light up, then put the black wire to the negative post, and the red to positive. That should hopefully tell you what you need to know about how it needs to be hooked up. Since it's only 12V, you don't have to worry about getting shocked; you can just use your hands to touch the wires to the posts.
Ta-da! Good luck!
 

VonYinzer

Over 10,000 Posts
Just remember that your mounting bolts are your ground...

If you mount the light to fibreglass, you'll need to run a ground wire from one bolt to the frame or no lights...
 

theconjuring

Active Member
thanks for this thread. noob here as well.

what I get from here is that my ground wire ( which is the short one with a circular connector) should simply be hooked up to one of the bolts that are mounted to my fender...

is that the case with all electrical on the bike? the ground should simply be attached to any metal part?( frame, fender etc..)

63-16039.jpg
 

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