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MG MGF Technical - MOT failure:- dim headlamp

My P-reg has just failed its MOT due to dim o/s h/lamp and indistinct beam pattern.

I've checked the wiring and have 12V at the bulb but even with a separate earth back to the body, it still looks dimmer than the n/s lamp.

Any ideas what/where to check?

Also, there is no clear cut-off to the beam; does this mean I need a new h/lamp unit?


You could try swapping the bulbs over and see if the problem moves with it? (you might even try the main beam bulb with it, if they're the same - which they are one some cars).

Maybe also a "take apart and clean" is called for - you can get the glass off the front, and wash the inside of the lens, reflector and glass.

Maybe also measure the current that the bulb is drawing and compare with the other side - you know the voltage, times it by the amps and you should get an answer around 55 to 60... (i.e. around 5 amps).

Try asking a metro mechanic: metro's have the same sort of lens arrangement in some varients, I believe, (as do the new minis!) - and sometimes the light barely "falls" out of them!

Good luck...


Also try running a wire between the earths of both lights, if you have an earth fault then this will show by the light regaining brightness.

Could also be the 'milky lens' syndrome but I would be surprised if it wasn't the same on each side.

Is the voltage exactly the same on the two dip beams?

If all else fails you could buy a brighter bulb. Ring R481 100w if you have H1s fitted.

Bruce Caldwell

Just checked the voltage on my dip beams. Between the battery and the dip beam bulb there is a drop of 0.865volts. If you count watts as brightness then this indicates a loss of 6.4% brightness by resistance in the switches, wiring etc.
Perhaps the insertion of a relay close to the headlight units would alleviate this volt drop?

Bruce Caldwell

It could be the same problem that I had on my '98 S redg VVC when it was MOTed six weeks ago. The silvering inside one of the headlamp units had deteriated. It wasn't visible thru the lens but it did mean that the light was dimmer and had no defined pattern and thus failed the MOT.

My (rather expensive) solution was to buy a set of new Trophy headdlamps from B&G.
Mark Turner

My 97 P-reg also suffered from terribly dim headlights, which obviously was a gradual deterioration... I only noticed after driving my wife's car one night and realising I could actually see where I was going. I wouldn't recommend my solution though - drove into the back of someone on a roundabout (in broad daylight)...

For those new to the BBS older cars do suffer from milky dipped beam lens as Bruce has already mentioned (my car is a 1996). I rarely drive on country roads at night but when I did a few months ago the drive was truly terrifying. Unfortunately the inner lens cannot be cleaned, the milkiness is a result of deterioration of the glass lens itself, these lenses are not sold separately. My solution was to buy a new pair of head lamps 160 for a pair of brand new assemblies. The lights are superb. A bit cheaper than the TF conversion! Takes about 45 mins to remove the front bumper and swap the assemblies.
tim woolcott

Thanks everyone.

I ended up changing the headlamp as the reflector had deteriorated to a matt finish.

Only trouble is that the n/s lamp looks to be suffering from the same problem so , I guess , I'd better check it carefully before next year's MOT.

Rgds, Tony



I run a Trophy race car and would be very glad to receive donations of 'milky' headlights as spares (if the racing this year is anything like last year, I may need several!). I can cover carriage and packing costs and maybe even find you a free ticket for an MGCC Championship race meeting. Look forward to hearing from you!


Richard J.
Richard J.

This thread was discussed between 20/03/2003 and 28/03/2003

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