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MG MGB Technical - Headlights don't work, but high beams do

This is driving me nuts. My headlights are not working, but when I hit the switch for the high beams they work perfectly. All my other lights (front, rear, side marker) all work normally. I thought it might be the switch so I tried just hooking the wires into the new switch this weekend - again, headlights are not working but all else (including high beams) do.

What am I missing?

Robert
Robert Rushing

The power for the low beam goes thorough one of the famous Lucas bullet connectors located just in front of the radiator support on the right side. The wires from both lamps go into one connector. It's quite possible that you have a poor connection at this location.
Bill Young

Robert,

When you say..."when I hit the switch for the high beams they work perfectly" do you mean when you hit the "flash to pass" switch on the steering column?

If so, and given that the other lights work fine, the only source of trouble could be the blue wire from the headlight switch to the dimmer switch.

The "flash to pass" circuit gets its power from a different source than the regular headlight switch. Power to the dimmer switch comes from the blue wire from the headlight switch.

What year is your car?
Dan Masters

It's a 71. I can either use the "flash to pass" pulling the switch back or can turn them on full time by pushing the switch forward. Either way the high beams work fine, the low beams don't work at all.

History: this is a new harness I put on about 4 years ago when I restored the car. Everything has worked great until this problem cropped up a few weeks ago.

Robert
Robert Rushing

Robert,

In that case, you have a problem in the blue/red wiring from the switch. Check the blue/red wire as it comes out of the switch. With the main switch on, and the dimmer switch in the low beam position, you should have voltage on this wire. If not, the switch is bad. If you do, then you have a bad connection in the blue/red wire circuit, somewhere between the switch and the headlights. Just keep tracing the blue/red wire, from the switch to the headlights, with a voltmeter until you find the point at which you no longer have voltage. There will be your break.

The connection that Bill mentioned is a very likely source of the problem, so you might want to check there first.
Dan Masters

Robert,

Try looking at the wiring mess under the front latch cover. I can't remember but I think the low beams are the blue with a red trace. Jiggle it around a little and see what happens. After a while you get a little corrosion in the connections from water coming in through the grill.

Luigi
Luigi

Thanks guys! It wouldn't surprise me that all that mud that got in there during the Lap of the Lake endurance rally finally caused a problem...

Robert
Robert Rushing

re: It wouldn't surprise me that all that mud that got in there during the Lap of the Lake endurance rally finally caused a problem...


Robert....It's not my "fault"!!!!!!

bRick
bRick

Yeah, I know. It's my fault. First, it's my electrical fault. Second, it's my fault for not listening about "seasonal roads", and third, it's my fault because I probably pulled something lose when I pulled the engine for the new clutch.

But that doesn't matter right now - bRick, why are you typing here instead of finding out if you've got to get chopped on?

Robert
Robert Rushing

Usually it is a broken wire on the column switch - if you are careful you can solder it back on - otherwise it is a new switch...
Chris at Octarine Services

What's your charging voltage--I had a regulator fail years ago --was putting about 16-18V into the lights. Over a period of time I burned out just about every filament (except the high beams, which I seldom used)) in the light system. A volt-ohm meter is the most imortant tool you can have when troubleshooting anything electrical. I prefer an analog meter for most work, as you get an instantaneous reading.
R. L Carleen

Robert - friend of mine had a similar problem and spent two days troubleshooting - then brought it to me and it turned out to be two burned out low beam filiments. hope this may save you some time - try checking head lights.
Fritz Warner

I had the same problem on my 75B. The dipped beam contact in the switch gets bent back when the headlights are flashed & should spring back into place when the stalk is released.
I found that the contact in the column switch was not springing back far enough to maintain contact. My solution was to bend the contact back into position with a thin pointed object.This has worked for about 2 years now.
If you try this, make sure that whatever you use to bend it is made of wood, plastic or some other non conductive material or you could cause serious electrical problems / sparks / fire!
IR Tapner

Robert...

I go under the knife on Wednesday, February 9th. I'll be in a full arm cast for 3 to 4 weeks, then physical therapy and rehab.

I will be at the MER...Handicapped Division this year!

;-)

bRick
bRick

I had similar problem,i change the bullet type connectors at front grille, and cure the problem.
But i still have another, the inside indicator light does not go intermitent when in use, both directions.
Alf
ALfredo

Alfredo - what year? On most cars if the corners are flashing there is no reason why the tell-tales on the dash should not be as well, but early cars had a different flasher unit with a separate contact to power the tell-tales, this may be faulty or incorrectly wired.
Paul Hunt

New jackets and dialectric grease can be a big help - and a cheap one, too!
Adam Birnbaum

This thread was discussed between 31/01/2005 and 08/02/2005

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