Simple number plate light issue

[firefighter]

Before I write this, I could go through the hassle of splicing every damn wire until I get it right, but i'm sure one of you can answer this for me easily enough.

I have put an after market undertail/tail tidy on my bike.

The original set up had no individual number plate light, just clear lense at the bottom of the original tail light to light up the plate. (clear as mud?!) So in other words, the bottom of the red plastic tail light cover is clear.

Now, I have had to add a number plate light to my undertail, and since there is no original seperate wiring for the no. plate light, I spliced the new plate light into one of the tail light blubs' positive and neg wires.

Here's the problem, the light goes, but when I apply the brake, the no. plate light stops, then comes back on when I release the brake, everytime a coconut.

There are three wires going into each tail light, two are straight to the bulb, and one is off to the side for each one, now i'm assuming this is a constant? should I have spliced my no plate light into this?

The wires I used were from one tail light, the ones going straight to the light, not the one off to the side. Should I have spliced into the one on the side, and if so, being there is only one wire, and the no plate light has two (red & black) what do I do with the other wire from the plate light?

This is far more simple than i'm making it sound, I could just start splicing and guessing etc, but as it's all installed it's a bit of a bastard to get at, and as I said someone should hopefully be able to answer this for me relatively easily.

Cheers.

[imdying]

$20, get yourself a multi meter. Find the wire (of the three) with zero resistance to ground in both states. Then find the wire with 12v with the brake both on and off. That's your ground and 12v, which is all you need. If it's a Suzuki you might find that they're Black/White (ground) and Brown (or maybe green) (tail light). The other one should be White/Black, which is 12v switched for the brakes.

[neels]

Sounds like you have connected to the tail light and brake light wires, rather than the tail light and ground wires. The one wire of the three that you didn't use should be the ground, so wire this to one side of the number plate light, then turn on your tail light and connect to the one of others that makes the number plate light go.

What you have at them moment is 12v from the tail light circuit on one side, and the number plate light finding ground through the brake light filament, when you brake you have 12v on both sides of the number plate light and it no go.

[CookMySock]

Both posts above get it right. The test light is almost more useful than a multimeter though. While the multimeter has more features, it can be confusing for the layman to use, on account of it's high internal resistance.

The test light is more intuitive to use, and its quicker and more robust, and it doesn't lie to you in high-impedance circuits.

Steve

[NinjaNanna]

There are three wires going into each tail light, two are straight to the bulb, and one is off to the side for each one, now i'm assuming this is a constant? should I have spliced my no plate light into this?

The wires I used were from one tail light, the ones going straight to the light, not the one off to the side. Should I have spliced into the one on the side, and if so, being there is only one wire, and the no plate light has two (red & black) what do I do with the other wire from the plate light?

This is far more simple than i'm making it sound, I could just start splicing and guessing etc, but as it's all installed it's a bit of a bastard to get at, and as I said someone should hopefully be able to answer this for me relatively easily.

Cheers.

I assume the number plate light is an LED one and has a red and a black wire? If so leave the red one spliced where it is and splice the black one into the wire that goes off to the side.

As others have explained the 2 wires going straight to the bulb are the Stop lights and tail light connections - the one going to the side will be the common ground.

[firefighter]

Cheers all. I actually blew the LED. I did'nt actually know it was possible. I checked it, then re-wired it and it stopped working. Was kinda a good thing as I found one which looks a lot better anyhow with the new undertail set up I have. It works fine and does'nt go out when I put on the brakes! Hahaha. So all sorted. (funny the original one only blew when I hooked it up the right way!??)