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MG MGB Technical - Headlight Switch @72 GT

Last week the main beam failed but the dipped headlights and headlight flasher worked. This fault was traced to the steering column mounted switch. There appears to be no breakages in the switch.
Currently:
a) with the dash light switch OFF the main beam works by putting the switch arm into the high beam postion.
b) when the lights are switched on and main beeam selected the dipped beam remains on with the main beam lit. Thus all the elements in the bulbs are ON.

Can anyone explain how this switch operates so I can effect repairs or does anyone know of a suitable web site with diagrams etc?
2. Can this fault be fixed or have I got to spend another 40/50 (up to $100) to replace the switch. The current switch is about 2 years old.
Bob Marshall

Dear Bob,

I too have a 72B (roadster) and have had a similar problem with the light switch. My car was restored in '04 with a new (MOSS) switch which failed after about 6 months. It was replaced and again, after a few months, the switch failed. It would only operate with high beams. No low beams. Rather than buy a new switch I removed the steering column cowling and was able to see that some of the "contacts" were not making contact when they should. I was able to bend them back into a position for solid contact and now the switch works fine in all positions. I wish I could tell you the exact layout of the switch contacts but as I remember, it was relatively easy to figure this out by examining the switch contacts with the arm in its various positions - high beam, low beam, and flash to pass, and then making the necessary adjustments. Hope this helps. -Chris
Christian

Bob; Chris has the answer, when you remove and examine the switch you will see which contacts need bending or cleaning. I don't know of any web site with instructions or photos.

Clifton
Clifton Gordon

http:/www.advanceautowire.com click on stock schematics
The above website has wiring diagrams available.
Some people have installed relays to reduce the electrical load going through the switches. Look at the installation instructions for headlight relays, you will find a wiring schematic for the relays.
Kimberly

Thanks for your tips. How do you know which way to bend the contacts. A colleague (of impeccable MG lineage a K3 J2 etc etc) and I spent 2 hours bending etc with not much success. Does anyone have an idiots guide to this *?*!?!! switch?
Bob Marshall

The dip-switch switch isn't really meant to be repaired, just replaced, which isn't cheap. The switch is *supposed* to operate as follows:

Clicked away from you it should stay in that position and that powers the main beam. Clicked towards you again staying in that position it should power the dipped beams. Both these are only when the main lighting switch is fully operated (i.e. not just half operated in the parking lights position). Pulled towards you and held there against spring pressure it will power the main beams, whether the main lighting switch is on or off, and this is the headlamp flasher. If the main lighting switch is *on* then you will get all four beams powered. Releasing the lever spring pressure will take it back to the central position extinguishing the main beams, and leaving the dipped beam on if the main lighting switch is fully on.

It sounds like your switch has lost the return spring in the headlamp flasher position and so is 'sticking' in this position. As such it may be that no amount of bending contacts will effect a repair.
Paul Hunt 2

Paul
Thanks for your notytes. There are two points on the end of sprung arms and two contacts, one above and one below. What position are these in for dipped and main beam?
Bob Marshall

What color are the wires that connect to the two contacts you have questions about? When the switch is held towards you, it is in a momentary on position connecting the purple wire to the blue/white wire. When the switch is pushed away from you, the blue wire is connected to the blue/white wire. When in the neutral position, the blue wire is connected to the blue/red wire.
Kimberly

As Kimberley says, plus when pulled towards you to connect the purple and blue/white together, the blue and blue/red are also still connected together. I have got an old one lurking in the garage somewhere, I'll root it out and see if that can shed any further light (ho ho ho! (to be seasonal)).
Paul Hunt 2

I lost the high beams on the 70 B I care for. The main driver tended to hold the switch in the 'flash' mode to compensate, which was cumbersome. While installing a new steering wheel, I solved the problem by removing the switch and removing the spring contacts between the blue and the blue/white (high beams) and blue/red (low beams) wires. Bench tested with a multi-meter and reinstalled.

Removing, rebending and replacing the spring contacts required removing the head of a rivet, and replacing the rivet on assembly with a small screw and nut.

Pictures are:
http://i44.photobucket.com/albums/f33/dave4419/MGB/switch_w_faulty_contact.jpg

and the following two pictures.

warmly,
dave

Dave Braun

whoops, evidently I have to link each picture separatly. Here are the other two.

http://i44.photobucket.com/albums/f33/dave4419/MGB/contacts_apart_4_adjustment.jpg

http://i44.photobucket.com/albums/f33/dave4419/MGB/switch_repaired.jpg

dave
Dave Braun

Pictures of mine at http://www.mgb-stuff.org.uk/dip.htm

But if the arm doesn't move properly i.e. click between the dip and main positions, and pull against spring pressure from the dip to flash and return when released, that is another issue. You would have to remove the roll-pin from the arm pivot, and you would then probably find a spring and ball in the arm pressing on some notches on the body of the switch. It these three components that give the clicking and spring return action, not the switch contacts.
Paul Hunt 2

Very nice pictures Paul. My recollection was that the dip feature click was a plastic on plastic click. I'm not certain there was a spring or ball involved, but I don't have a spare switch in front of me.

warmly,
dave
Dave Braun

Could be, that is from memory and so could be something else, I didn't dismantle this switch this time.
Paul Hunt 2

Thank you for your help/advice.
We traced the problem to the small brass leaf spring which activates the opening of the points between the BLUE and BLUE/RED wires. The breakage of this small item, which is non repairable has cost me another £40/50.
Moss claim that these are genuine Lucas parts. They come in a Lucas marked box but I suspect they are not genuine Lucas. The new one has different thread types for the securing scews and there are chips on the bakelite body. Strange. We used to make very complex equipment will small sensitive parts which a client would expect to work uninterrupted for about 15 years. Another company I worked for made engines which would work for 40/50 years in poor conditions with effectively no service.
Bob Marshall

This thread was discussed between 27/11/2006 and 01/12/2006

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