Question on two-wire brake/tail light...

[TeeCat]

Greets, all...

I'm mounting and hooking up a new Mike's tail/brake light on my experimentally bobbed fender after having been hit in the rear two weeks ago. I have sorted out the mounting issues, but have a wiring question.

My '73 harness uses three wires, as did the last light I had from Mike's, which was too damaged to re-use. The new light, however, only has two wires. I suspect that one is tail light and one is brake. My question is whether one of these wires also serves as a ground, and how would they connect to the existing wires from the harness, or whether I need to add a ground.

If I do need to add one, there is a bit of an issue because the body of the light is alloy. The bolts that actually affix the light itself to the are steel, but the threads are so close to the inside body of the light housing that I can't get a nut on it to affix a loop or horseshoe terminal. Any other ideas for attaching a ground to a bolt's threaded end... some kind of clip, perhaps, that I could crimp to the light end of the ground?

If I don't need to add a ground it will be a non-issue, but I suspect I will. This light mounts on rubber, so I don't see how it can ground through the light body if it's alloy. Is it conductive for this purpose?

Thanks!
TC

 

[Downer]

Deleted sorry should of read whole post

 

[nj1639]

I just checked 2 stock tailights that I have laying around and the bulb socket has a tab on it to attach the ground wire to. If you don't have a tab for the ground then anyplace on the light that would give you continuity to the bulb socket will work regardless of rubber mounting. Check continuity with an ohm meter. How did your last ground attach?

 

[pamcopete]

You have to run a separate ground from the frame to the socket. There may be a tab on the socket for the ground. One of the three wires from your stock wiring was probably ground.

The fender itself is not a ground because it is mounted to the frame with rubber insulators. You may in fact measure a ground on the fender, but that is what is known as an incidental ground perhaps created by the rubber insulators being torn and allowing the bolt to make an incidental connection between the frame and the fender.

 

[nj1639]

Yeah Pete.....to add- I replaced my stock light with a lucas repro..2 wires from the bulb. I used the ground wire from the original harness the travels under the rear fender, and grounded to one of the tail lights fender mount bolts with a circular clip. Of course there is continuity from the mounting bolts to the bulb socket.

 

[jayel]

I just put a Lucas replica tail light on my SR500 drilled a small hole into the back inside, used a sheetmetal screw with a wire end to attach as ground

 

[TeeCat]

Hi, guys... and thank you.

While you were replying, I took my test light and identified the harness-side hot wire, brake switch wire, and ground. Happily, all three survived the mishap with their female terminals intact. So all I'll have to do is plug in the males from the light once I establish a ground wire. I'll have to look for a tab... didn't notice one.

Of course there is continuity from the mounting bolts to the bulb socket.

This would be good news, as it would mean that if I can find a suitable way to fix a homemade ground to threads on one of the bolts that mounts the socket assembly to the housing (or to one of the housing mounting bolts as long as the alloy housing is conductive), then I can just plug the other end into the harness ground like I did with the three-wire.

Just to be sure about the continuity between mounting bolt and socket, I can test this with a meter, right? What would continuity look like on a digital meter?

I just put a Lucas replica tail light on my SR500 drilled a small hole into the back inside, used a sheetmetal screw with a wire end to attach as ground

Good idea, jayel. Might could do that if I had to. Does it matter if the body is alloy? Not sure how I got that in my head.

TC

 

[nj1639]

I use the tone side of the meter. Set to ohm and touch the terminals together...should beep, at least mine does, then when you touch the terminal to point 'a' and the other to point 'b' you'll get a beep if there's continuity.

 

[TeeCat]

Thanks, sir... I'll try this tomorrow. Not sure if mine has a beep.

 

[jayel]

meter will go to 0 or sometimes I (infinity) could put a loop terminal on underside of fender bolt with a plug-in wire back up thru the wire hole to tie into the loom ground, I was thinking if you put in under the lamp body it would raise one side

 

[TeeCat]

meter will go to 0 or sometimes I (infinity) could put a loop terminal on underside of fender bolt with a plug-in wire back up thru the wire hole to tie into the loom ground, I was thinking if you put in under the lamp body it would raise one side

jayel, I'll likely do your suggestion of a loop terminal on one of the mounting bolts between the fender and stop nut (under the fender). I was fooling with my meter and, when the leads are apart, Ohms/resistance setting and power off, it reads 1, but when I measure from either lower mounting bolt to the leads, the meter reacts (variable reading, but consistent reaction), which I suppose means I can use those bolts for one end of the ground. I'll whip up a ground lead tomorrow and try it.

 

[jayel]

jayel, I'll likely do your suggestion of a loop terminal on one of the mounting bolts between the fender and stop nut (under the fender). I was fooling with my meter and, when the leads are apart, Ohms/resistance setting and power off, it reads 1, but when I measure from either lower mounting bolt to the leads, the meter reacts (variable reading, but consistent reaction), which I suppose means I can use those bolts for one end of the ground. I'll whip up a ground lead tomorrow and try it.

bet it's a I (eye) not a 1

 

[TeeCat]

So if it's an I, that would mean the circuit's open with the leads apart, right? And if I'm getting a reading when testing between A and B, there's continuity?

 

[aldo5468]

I had the same issue with Mikes #11-2269 tail light, which I'm installing on my '82SJ. I replaced the 2-wire socket with a 3-wire OEM Yamaha socket from a Virago front signal (had a couple from a previous project). Also got Mikes #112-0629 coupler set - I'll attach the male side to the taillight wiring and plug it into the original female side in the wiring harness - using sections of blue, yellow and black wiring taken from a spare 650 wiring harness to extend the new tail light leads, it'll look as close to "factory" as I can get it. It just doesn't make sense to me that the tail light isn't sold upfront with a 3-wire socket, when it obviously has to serve as both taillight and brake light - so what if it cost another buck or two? It would save cobbling a ground.

 

[jayel]

So if it's an I, that would mean the circuit's open with the leads apart, right? And if I'm getting a reading when testing between A and B, there's continuity?

yes and yes... I = infinite Ohms = open circuit... reading indicates readable Ohms (resistance) the lower the better in this case

 

[TeeCat]

It just doesn't make sense to me that the tail light isn't sold upfront with a 3-wire socket, when it obviously has to serve as both taillight and brake light - so what if it cost another buck or two? It would save cobbling a ground.

I could not agree more, but cobbling a ground should not be too much of abn issue, I hope. Just seems like unnecessary trouble, though.

yes and yes... I = infinite Ohms = open circuit... reading indicates readable Ohms (resistance) the lower the better in this case

Well, we'll find out tomorrow... I suppose the worst that can happen is I'll blow the fuse if the ground's insufficient.

TC

 

[TeeCat]

Guys, once again, thank you... I think we have success. I made up a ground with a loop and a male terminal, and attached the loop end to one of the mounting bolts for the light. To be safe, I used my meter to check for continuity between the male end of the homemade ground and the female end of the harness ground; it went consistently from I to 0.00. So I hooked up all three wires, turned he key on (motor not running), and we have tail light and brake light, and no blown fuse. So I think I should be good to go in this respect.

I finished bobbing my rear fender, which was damaged in the rear-end collision, and I'm pleasantly surprised at how well it turned out, and how well it accepts my new tail light. I just wanted to see if I could bob a chromed fender before replacing it, and I'm glad I tried. Now I just have to secure the wires and replace the T-clips on the displaced seat trim with button-head machine screws, and I think I'll be back in business. Pics will be in the "mishap" thread when I'm done.

TC

 

[jayel]

Aye, that will teach you not to back into minivans

 

[PetesPonies]

Tee, where did you get rear ended?? yikes !! glad all is well with you.

 

[TeeCat]

jayel, right you are!

Hi, Pete! I got sodomized by the classic "overstimulated, under-attentive professional woman in sport ute" Saturday two weeks ago. Not too much damage, and I wasn't hurt, thanks. "Before" and "after" piccies later in the week when I get her all buttoned up. (We still need to hook up, mate.)

TC