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MG Midget and Sprite Technical - Poor Headlight Brightness

I noticed recently that the nearside headlight was very dim on my 1500, so assumed the bulb had blown and the dim light was coming from the side light bulb. On replacing the bulb it again appeared very dim, on closer checking the dim light was coming from the main bulb and the side light was also very dim.

All the connections appear OK and the right side lamp is good and bright. Do the two headlamps work off the same earth connection, if they do I presume there's a bad connection somewhere, but was hoping it may be a poor earth wherever that is? When the main beam is turned on the faulty nearside light goes out completely.
Tim Lynam

Definitely sounds like a bad earth. There are three wires on the headlight bulb, one for dip, one for main, and the earth which will be a black wire.Follow the cable that comes out the back of the headlamp and see where it goes. At some point, probably behind the grille, the black wire will emerge from the cable and will be bolted to the body. That connection needs to be clean and tight with no rust or paint between the ring connector and the steel of the body.
Mike Howlett

Tim, l think this is likely to be a poor earth connection. A quick and easy check into get a length of cable, bare the ends. Then with the headlights switched on touch the cable ends onto the battery negative post and the metal of the headlight rim. If the bulb brightens, it confirms the fault is a poor earth and you can proceed to attend permanently to that as Mike describes.
GuyW

Thanks Mike & Guy, great clear info, will check the earth connection.
Tim Lynam

I don't think that grounding the headlight rim will do much.
Dave O'Neill 2

Best/easiest/cheapest way to improve headlamp brightness (if the earths are good) is to install the relays that BMC/BL strangely decided were unnecessary. Made a big difference to mine.

FWIW the last time I had this problem was on my mate's GT6 and it turned out to be a grungy lamp socket. Just dirty - that's all.

BTW it doesn't sound like bad earth to me if the high beam is good - it uses the same earth connection.
Greybeard

If the nearside goes out on main beam then it is definitely the nearside earth.

If it is the same as on the B (long time since I played with the midget's electrics) then the black wire from the n/s headlight goes to a 2 way bullet connector on the nearside under the slam panel and thence to a 4 way bullet connector on the offside where it joins into the black wire from the offside headlight.

Either of the two connectors could be a bad connection - pull the bullets out and clean them up - replace the connector if it is rusty inside.
Chris at Octarine Services

I agree it sounds like a bad earth. The main beam takes more current so will go even dimmer, or off altogether, as you are finding.
W Bretherton

Even with a very good earth in a new electrical standard system, I measured a 1,5 volt loss in the spridget electrical system. Loss is in connectors, adaptors, switches and the diameter of the cables. If you switch tot relays, expensive 2,5 mm2 cables and solder all connections you will get two times more lumen! If you used an older system it is even more.

Flip
Flip Brühl

I was puzzled by your comment Dave, as mine definitely went brighter when I used a temporary fly lead as a test earth to the rim. So I have just had a quick look at one of my headlights. It has a short earth connecting wire inside the metal headlamp bowl as well as a black wire that disappears into the loom. I assumed they were all like that? But since I rewired this car with a complete new loom when I rebuilt it maybe I added that link in as an extra earth at the time. I don't remember doing so but that doesn't signify anything these days!
GuyW

Oops I misread the original post.

If the car has the original bullet connectors that Chris mentioned they are worth a good coat of looking-at, being notorious for going high resistance.

As noted a good clean generally does the trick, but I usually replace any that start giving trouble.
Greybeard

You could have the 3 wires to that headlight unit wrongly connected.

Rob
MG Moneypit

As always I'd go with make sure all connections are clean, secure and protected. (ETA: and correct to follow Rob)

Having done so once I wouldn't rush to use new modern made bullet connectors as they don't seem to be quite the right size so clean and tighten (if possible) what's already there. I like to use a dab of contralube to help protect the connection but other stuff can be used.

Guy,
sounds like you did add extra earths, you can join my memory group, we meet on er, ?, well at er, ?, oh, don't worry no one remembers to go anyway ...

or is that for the other group(?).
Nigel Atkins

I think that may have been the other group Nigel, or is ours the other one? I did for a long time keep a diary of work l did on the various cars in the family as once you've fitted new brake pads with your head under the wheel arch, it's quite hard to recall which of several cars it might have been, or when. But lately l forget to fill in the car jobs diary and anyway l cannot remember now where l put it!
GuyW

They say if you have a bad memory to make lists but if if you do remember to make a list then you can't find it, and don't ask me who "they" are as I can't remember.

Thinking about it perhaps they didn't say to make lists(?) ...

I can't remember if I'm going up the stairs or down the stairs and I live in a bungalow.
Nigel Atkins

Thanks for all the answers.

The near side earth connection to the body looked a bit corroded so changed the rusty screw and cleaned the connector and checked both lights when the earth was disconnected and both went out, so I presume the one earth to the body serves both headlights and the earth now appears good, but still one good light and a very dim nearside light.

Cleaned the earth bullet connectors, but still no improvement.
Tim Lynam

Just a long shot Tim. My lights started doing all sorts including dim at times. It was the rocker switch which after some messing with as I thought the connections were playing up fell apart. What a pain! I recon it only lasted 39 years!
Dave Squire

Tim,
keep going back with the earths and connections, if required include the main light switch, panel lights switch, column stalk switch, the fuse and fuse box connections (for the side light) until you reach the battery and main earth leads. You may find poor connection(s) even though they look good and/or you might discover wrong or added connections or wiring (have your Driver's Handbook wiring diagram to hand obviously).

With things like light switches that don't get used a lot it pays to now and again rock them on and off a good few times to help keep the switches working, good time to do this is when you have the battery disconnected.

It also pays to regularly test the horns, hazards, wiper motor and washer, perhaps the heater motor fan and reversing lights fairly regularly - easiest way to test is, if you can, whilst using the car regularly. ;)

Nigel Atkins

Tim,
If the off side lamps are all working correctly (Main, dipped and side lights) then the fault is somewhere further down the loom towards the near side lights themselves. As you have replaced the n/s bulb you can probably, though not certainly, eliminate the bulb itself. This leaves only:
1. Earth connections. Double check that the earthing wire from the n/s light is making a good contact with bright steel on the bodywork. If in doubt try a fly lead direct back to the battery negative post.
2. The light bulb connector with its 3 connector socket. Are the contacts in there sound and clean. They are prone to corroding.
3. The bullet connectors back up the wiring loom, but downstream as it were from the o/side lights. There is a group of connectors for all of the n/side front lights and indicator in the wiring harness behind the radiator grill. You may need to remove the grill to get at them. They need to be clean, firmly connected and ideally once checked they then should be bound around with waterproof tape (self annealing tape is best)
GuyW

Tim, I'm know convinced you have a bad connection somewhere between the earth terminal of the dim bulb and the chassis earth. Try a temporary earth connection from the bulb terminal by temporarily putting the bulb connector on the wrong way round (for a conventional 3 terminal connector) if you can I.e. so only high beam or dip is connected and you then have access to the earth terminal. I doubt it's the switch as both lights would be affected.

Bill
W Bretherton

Gday all I have a dim memory of changing all the wires to the headlights and duplicating the earth wires, one for each side, when I fitted the relays. The earth wires had what I describe as "black wire disease" the copper having corroded and gone black. All bullet conectors were cut off and replaced with spade connectors, soldered and heat shrinked. I fitted new headlight buckets. The 3 pin headlight connectors were OK, strangely enough. My 1500 had sealed beams which were in good nick so retained.
I know, a lot of work, but the lights are as good as can be expected without recourse to semi sealed and Halogens.
Cheers
Rod
R W Bowers

Checked the earth connection at the bulb by attaching one end of wire to the earth connection at the bulb and the other end direct to the earth battery connection and hey presto the bulb was back to being nice and bright.

The fault was down to the earth connector being corroded on the plastic 3 pin block which attaches to the bulb, a quick clean and the bulb was back to full brightness.

To all that said it was a bad earth I owe you a pint you were spot on, a simple fault but one that was so frustrating to find the cause of especially just before the MOT, all the replies were much appreciated.
Tim Lynam

This thread was discussed between 16/04/2017 and 19/04/2017

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