Number Plate Light Confusion!

Bonnie1980 · May 23, 2022

Hi all,

So my T120 Black failed its first MOT. Main reason being there is no number plate light. I have an after-market tail tidy.

I got a stick-on number plate light from Amazon which works a treat. I connected it to the auxiliary wire on the after-market rear wiring harness, which already powers my rear running and brake lights, and the left + right indicators.

The issue is that the number plate light stays ON all the time when the ignition is ON. I would have thought that it should come ON only when the headlight or the parking lights are turned ON

Questions:
1. Should the number plate light be ON at all times?
2. If the answer to the above question is No, then which wire should I connect the number plate light to?

Any thoughts or advice is greatly appreciated. Thanks.

Iron · May 23, 2022

From the mot gov whatsit site

Position lamps (I'm assuming headlamp/s) don't come on with the ignition. So you need to wire the plate illumination light along with the back light rather than just power from the ignition.
Have a look at the wires that feed into the back light bulb. I've no idea what they look like on yours but I would expect one for the brake light, one for the light (when you turn the lights on) and an earth (unless it earths through the bayonet fitting or whatever new fangled thing you have for LEDs and the like and then through to the frame). Find the wire for the back light only and connect the live for the number plate light to that.
If your headlight comes on with the ignition as vehicles after 2018 do I think then it shouldn't have failed in my opinion. I'd be finding another MOT dipstick anyway if he's checking that. Cause the way I read it is it has to be on with the headlight and as it's on all the time then it's bloody on aint it?

Bonnie1980 · May 23, 2022

Thanks @Iron for the reply. The Major fault I got was:

(b) A rear registration plate lamp or light source missing or inoperative:
(i) when rear registration plate has 2 or more lamps or light sources

This was because I did not have any plate light at all. Just the tail light.

I guess what you mean is that the plate illumination light should be connected to the ‘running’ light at the rear- which is what I read in couple of other places online too. But then, I will have the same problem as stated in my initial post because my running lights stay ON all the time too.

I have the Motone wiring harness for T120 LC. The various wires are assigned as below:

Tail light -
RED - BRAKE Light
YELLOW - RUNNING Light
BLACK - Earth

Left Indicator/Turn Signal
BROWN - LHS Signal
BLACK - Earth

Right Indicator/Turn Signal
ORANGE - RHS Signal
BLACK - Earth

Auxiliary Live (this is what I have connected the plate lights to at the moment)
GREEN - AUX
BLACK - Earth

Is it normal for running and plate lights to be ON on a 2018+ T120 at all times?

Thanks again

Iron · May 23, 2022

From what you say the MOT guy has said you do not have a registration plate illumination light that works at all.
I'm afraid I do not know if a 2018 T120 has running lights on all the time. I assume you know, as they either come on with the ignition or you have to actually turn them on.
Either way the number plate light should be connected to the tail running light (yellow) so it operates at the same time. If you have running lights on all the time, then your registration plate light will also operate all the time.
As above, the rules say that is what's required.
Did you not question the MOT monkey about it? He should have explained it and what the solution is with you.

I believe simultaneously means - at the same time. So, if it's working then it should have passed. Or is it me being a bit thick here?

Edit:
Yep, just re-read, sorry it was me being a bit thick. I read that you had already fitted the amazon light before you took it for the MOT. Infact you are fitting it because it failed the MOT. I get it now, sorry.
Yes, wire it to the yellow (back running light) so it comes on with your running lights. Doesn't matter whether they are turned on or come on with the ignition. Apologies to the MOT knob as well (not really)