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MG Midget and Sprite Technical - Headlight Dimming

I have an intermittent problem with one of my headlamps and thought I would ask you experienced persons before I started taking things apart.

Every now and again when using the headlights, one (offside) goes very dim almost looks like a sidelight.
A reduction on battery power???? On other occasions the lights (both of them) will work fine.
This problem has happened two or three times now in the last four months.

Any clues on areas where you think I need to start looking???
Chris Guards Red Midget

Check the Earth connection.
K Harris

Earth. Or about 100 other Lucas faults. But I bet it's earth!
Rich Amos (1 Sprite 1 Midget!)

In a sealed beam unit isn't there the little bulb which shines through the clear spot at the back of the reflector in addition to the separate Side light unit.
This bulb illuminates the whole reflector and gives the impression of something akin to a dim-dip?

Dave
Penwithian

Dave on 1500s with no separate sidelight, yes. But 1275s and earlier don't have it.
David Smith

my vote

either bad earth

or bad bullet connector somewhere around the front end of the car

I've seen enough problems caused there to make number two my number one...

pull each one apart (including sidelights too, 'cos bad earths can cause drain through the sidelights too) and with a rolled up length of emery cloth or sandpaper clean inside the tube connector as well as around the circumference of the bullet piece

(get a few new connector tubes too, in one, two and three bullet sizes, because you are sure to find some that have broken)
Bill

If its a car with foot operated dipswitch then operate that switch 10 to 20 times and your problems will be gone.

Bas
Bas Timmermans

< when using the headlights, one (offside) goes very dim >

Sometime back on another thread here on the board someone made the point that, and I paraphrase: "bulbs don't go dim, they burn at full wattage or they burn out. Dimming is indicative of poor earth." Makes perfect sense to me, and I would add that a loose bullet connection (hot power) might either melt a wire or blow a fuse, neither of which would be an intermittent issue. I vote for bad earth.

R
Richard 1979 1500

>and I would add that a loose bullet connection (hot power) might either melt a wire or blow a fuse,

The electrickery cares not what side of the bulb it is, a bad upstream bullet will have a smiler effect to a bad downstream bullet.
Will Munns

Thanks for all your comments.

I will have a 'fiddle' next weekend after the old girl has dried out (went out today and got a little damp).

Cheers


Chris
Chris Guards Red Midget

If it's only one light that's playing up it must be a fault with the feed or earthing to that light. It can't be the dip switch or light switch or battery or generator/alternator. If any of those was faulty, both lights would show the same symptoms. There are three wires to the headlight bulb. One is the dip beam feed (blue/red), one the main beam feed (blue/white) and one the earth (black). Trace them back to their connection points. There will be a corroded connection somewhere.
Mike Howlett

< The electrickery cares not what side of the bulb it is, a bad upstream bullet will have a smiler effect to a bad downstream bullet >

A poorly made connection between battery and load is the same as a wire of insufficient gauge for the load: it overheats. If the connection is poor enough, the overheating will be enough to melt wire at the weakest link. Try running a big-load power tool on say, 28-gauge wire. same thing will happen.

R
Richard 1979 1500

Run a lead from battery +ve to the +ve connection on bulb, when headlights switched on. If the headlight becomes bright, problem is with the supply side. If not, change cable from battery earth and the bulb should brighten - shows problem with earthing.

BTW old bullet connnections between battery and bulb can easily lose 1V - that's 90% of power lost... so even modest improvements give good increases in light.

I recently cleaned up the thick/brown spade connection on the solenoid and 'saved' around 0.5V when lights powered...

A
Anthony Cutler

This thread was discussed between 24/01/2009 and 26/01/2009

MG Midget and Sprite Technical index

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