75 Sedan: Plate-lights, no voltage in the 2 black and red wires ?

[anderfa]

EU-control coming up shortly, and faulty lightbulb warning sign is showing on dashboard.

I have measured V on the wire-plugs, and almost nothing/0.1V etc.

A: Can I use some cables that goes further to the lock for the lid ? But will then the light on dashboard go away ?

B: Where can I find where those wires end up, to check voltage ? If it is bad connectione etc.

C: Can I connect the black and red wire together, will the light on the dash think the two 5A lightbulbs are ok now ?

D: Other places to temprary get power tp the plate-lights, that will make them work, and shut the light on dasboard ?

[Mike Noc]

More than likely a broken cable in the rubber bellows at the boot hinge. Are you measuring to good known earth or across the cables? If across the cables you may have a bad earth showing as no voltage, in which case it could still be a break in the cable or bad connection where it is bolted to the body.

[SD1too]

There is a printed circuit board (PCB) in the number plate lamp housing which is known to give trouble.

Originally Posted by anderfa

A: Can I use some cables that goes further to the lock for the lid ? But will then the light on dashboard go away ?

That's not the right approach. Initially remove the PCB for inspection.

Originally Posted by anderfa

B: Where can I find where those wires end up, to check voltage ?

The number plate lamp PCB is wired directly from the light switch module (LSM). Check voltage at the PCB connector (red/grey & black wires).

Originally Posted by anderfa

C: Can I connect the black and red wire together, will the light on the dash think the two 5A lightbulbs are ok now ?

No! That will risk damage to the LSM.

Originally Posted by anderfa

D: Other places to temprary get power tp the plate-lights, that will make them work, and shut the light on dasboard ?

Find the fault and repair it Anders. You will probably find a broken track on the PCB which you can repair with a soldering iron.

Simon

[Glen B]

You can buy an improved number plate light pcb from DMGRS. I fitted on of these a few years ago and have had no trouble since.
I can try and send a link but not good with technology. They are not expensive although not sure about postage cost to you

[vitesse]

Seen it many times and always wondered why you call your MoT an EU control, despite being free or non-members?

Anyway the solution is here:
https://www.the75andztclub.co.uk/for...d.php?t=159120

I was a bit lazy and soldered the new wires to the cleaned copper holders, but has worked for years.

Good luck

ps You might not know but there is a Norwegian 75/ZT group, here:
https://www.facebook.com/groups/153448372029381

[Glen B]

Just checked DMGRS website and can't find the uprated one on there now but if you google them and ring them they are very helpful. There is a genuine mg/rover new unit on ebay at present for £59 from XPart. It would be a quick fix until an uprated one becomes available.

[Glen B]

Just read ALL your post properly about make do and mend. My apologies.

[anderfa]

Thanks for all the fast replys, impressed :-)


-Actually, I had trouble with those lights 4 years ago. Was thinking rusted bulb-holders, so I routed a + red cable and -black cable directly from the wires with plug, through av hole behind the plate up to the left bulb, soldered on each side of bulb. Then soldered second red/black cable from first buld to second bulb.
Put tape on the bulb-ends before I pressed them into the holders.

I see Hantsdaves solution is much more elegant, would like to copy that.

This was working until quite recently, no warning light on dashboard.
So are we totally sure broken bulb in numberplate-lights will trigger the dashboard-warning ???



The first thing I did when both these bulbs didn`t work recently, I soldered in new bulbs, and checked with at battery on the wires red/black, and both bulbs lit up. But not when I connected directly to the plugs inside booth-lid.

Looked it again today with a collega at the work p-lot. He found by measuring that the black plug-wire from inside the booth didn`t have earth/ground, so probably broken somewhere on the way out to the plug.
Then he measured with my extra black cable clamped by a screw/earth in the booth, and thought my extra red wire from booth to lightbulb was broken, cause didn`t get signal/Volts.
So I will try to change that red wire first, to se if my old system works again.



"There is a printed circuit board (PCB) in the number plate lamp housing which is known to give trouble."
SD1too: I don`t understand there is a circiut board in there, isn`t just wires and bulb-holders ? So Hantdaves fix worked.

[stevestrat]

Originally Posted by anderfa

SD1too: I don`t understand there is a circiut board in there, isn`t just wires and bulb-holders ?

It doesn't really qualify to be called a printed circuit board. Its a mount for the bulb holders and carries the power from the wiring to the bulb holders.

[SD1too]

Originally Posted by stevestrat

It doesn't really qualify to be called a printed circuit board. Its a mount for the bulb holders and carries the power from the wiring to the bulb holders.

Hi Steve,

I found this photograph of it posted by T-Cut.



That looks remarkably like a board with tracks to me! It's even the standard green colour.

Simon