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MG Midget and Sprite Technical - Enlightenment

Took the midget out a couple of nights ago and was plunged into darkness when I put the lights on full-beam.
The dipped lights are OK, so didn't spoil the evening's run (except I couldn't go as fast as I would have liked).

First thoughts were, because it wasn't confined to one headlight, it's probably the dip switch.

Having poked around in the column switch (late 1500 with horn incorporated) using a test lamp, there is power at the purple cable terminal (live feed?) but none on the blue/white with the dip switch in the high beam position. Headlight flash position works OK.

Is this a failed switch, or is there some other possibility elsewhere on the circuit?

I upgraded to halogen lights a little while ago and they have been OK until now.

Any thoughts on this would be appreciated.

Dave, electrically challenged.
D MATTHEWS

If flash works but main not then the switch is broken
Get a wiring diagram (google is your friend)
Check what colour main is and search it on the switch (purple is horn iirc)
Look for any faults and repair where needed with solder
Onno Könemann

Seems to me that you have solved the problem without help. If you can not get the switch apart to clean/repair the high beam contact then it is probably a new switch. Halagon lights (Assuming they are the legal variety) will not place anymore load on the circuit when compared to the same wattage sealed beams.
Robert (Bob) Midget Turbo

Thee little button contacts in the switch unit that direct the current to the blue/white and blue/red wires for high and low beam are fastened to some pretty small brass spring strips. They easily get bent out of position and then the switch fails. This is especially prevalent on the aftermarket " patter" switches which in my experience are nothing like as robust as the originals, You may be able to get the original back to working condition by studying how it operates and then bending or re-positioning those small contacts with a mini screwdriver blade.

Guy
Guy

Guy's exactly right, I had the same problem on mine. I could get full beam on the flash but not the full beam switch. The little brass thingies had corroded and caused a slight melting of the surrounding plastic, so I replaced it with one form a Bedford CF (apparently they're the same!)

I've since relayed my high beams and what a huge difference that has made to the brightness.

Also running Halogens, as Bob has said, there should be no more current draw on them than standard as they are the same wattage, but I wonder if the way they switch on/heat up has anything to do with the perceived connection between the halogens and switches failing.
Rob Armstrong

Probably not relevant but also...

Check the bulbs, I often had what seemed to be a double bulb failure when I went to a breakdown which were probably the result of failures at different times.

A bulb might blow it's filament but because Halogens give out more light than tungstens the owners did not realise there had been a FAIL because there was still a reasonable light to drive with.

When bulb two blows suddenly there is a catastrophe and man thinks he has had a double fail.

As I say, it doesn't sound relevant here but worth remembering (before I FORGET)
Bill 1

You have a blue incoming fromm the headlamp switch which is then switched between blue/red for dipped beam and blue/white for main beam.

The purple incoming is purely to provide a feed for the headlamp flash when the headlamp switch is off.

Purple/black is the horn ground (switched).

If headlamp flash works OK, it's not the bulbs.

As above, sounds like the switch contacts.
Dave O'Neill 2

Hi Dave,
I had a similar problem a few months ago. There was a large delay in the high beam coming on. It turned out to be the contacts in the switch. I can't htink how they managed to become unadjusted but I adjusted them and the lights have been fine since.
The contacts in your switch may have become so far out that they do not make any more. Remove the switch from the column and have a look at what contacts make and which ones break when you move the stalk from dipped to high beam. If the high beam contacts don't touch when on high beam a little tweek with long nosed pliers will do the trick. Be careful though the contacts are quite delicate.
Good luck.

Dave
Dave Brown

Thanks everyone, plenty to think about there.

Had another poke around today with the test lamp. Incoming blue terminal has power but no power at the blue/white or the static and moving contacts of the high beam switch, so can only assume a break in the brass strip linking the incoming blue with the contacts of the blue/white. The whole switch assembly looks pretty complicated as far as taking apart and re-assembling is concerned, so it looks as though a new switch will be the order of the day.

Coincidentally I had a spare column switch (of unknown quality) which I tried, and it worked the high beam with no trouble. Unfortunately that particular switch has a fault with the indicator contacts so can't be used.

Thanks again,

Dave
D MATTHEWS

Well, a new switch ain't on the cards after all, unavailable new apparently.

It's the switch for a late 1500 (GAN6 2000000 on)and incorporates the horn button. Part no. is ADU 1021.

Does anyone know if this switch is common to other models of that era, Mini, MGB, Spitfire etc.

Or alternatively a source for a good second hand one?

Dave
D MATTHEWS

Well - I could have a look for you if you want ...! Which bit exactly do you need?
rachmacb

B hive has it listed(?)

possibly a nasty copy one one

http://www.mgbhive.co.uk/switches___horns.html
N Atkins

Rach,

The column switch is a complete assembly and comes with a short bit of loom terminating in a connection block.
The part no. is ADU1021.

Dave
D MATTHEWS

Sussex list it(?) - http://www.sussexclassiccar.co.uk/shop_factory_hazel/contents/en-uk/d854.html

can't find my never used compatability charts at the moment
N Atkins

Leave it with me - although the bhive might disagree! I'll try and get a look and see what's left of "Bitsa"
rachmacb

just in case rach hasn't got it

this one says Lucas on the box - http://www.leacyclassics.com/adu1021.html

another possibility - http://www.jagspares.co.uk/Abingdon/partdetail.asp?partno=ADU1021
N Atkins

Are you sure that the old one is beyond repair? They look a bit complicated at first, but if you trace through the wiring and contacts to understand how it works you will realise that they are really quite basic and simple. Unless part of the plastic has broken, the only thing that is likely to have failed is either the small contacts becoming corroded or bent, or the wire connections which are rivetted brass, may have failed. A bit of carefull work with a nail file and maybe a soldering iron should restore it to full working condition.

The replacement ones - which are still available - just don't seem to last long (even when they come in a Lucas box)
Guy

Having had a new stalk switch on my last car I agree with Guy and yes there's the 'new' Lucas not much cop and the old Lucas that's already lasted for years

you'll probably have to repair or tidy up the new switch anyway I had to
N Atkins

and then fit relays to stop it from burning out.
D O'Neill

Lol let me know if you get anywhere repairing it first!
rachmacb

Thanks for the replies folks,

Rach:- I've sent an email to MGB Hive, they list a new one so possibly might have a s/h.

Guy:- The contacts make and break OK, there's just no current flowing between the blue live feed and the switch contacts. They seem to be connected by a thin strip of brass which is concealed under the bakelite structure of the assembly. Does the plastic assembly come to bits? All the brass connections appear to be riveted on.

Nigel;- Sussex car parts list it but don't have one. There seems to be plenty of the earlier types available but I suppose as its the very late model, there weren't that many made.

Failing all else, the car has a motolita steering wheel for which I believe a horn push is available. It may be that I can pinch the switch assembly (with no horn switch) from my earlier car.

I'll keep you all posted.

And I will be fitting relays!!

Dave
D MATTHEWS

Lol I can go there tomorrow and sell them mine to sell you then :)!
rachmacb

Sorry Rach,

Perhaps I misunderstood you. Do you actually have that particular switch for sale? In which case I would be interested. My chances of repairing the existing are exceeding slim. Dave
D MATTHEWS

Lol Dave no worries - I didn't get chance to check that the switch is ok and all there today so I can't promise but yes I have a spares car that some have had odd bits from! On the other hand there is nothing more satisfying than having a jolly decent blast of a horn on the steering wheel when you need too so I would totally understand if you went that direction!
rachmacb

Rach,

Changing to the steering wheel is a last resort. Please let me know when you've checked your switch is a good 'un

Dave
D MATTHEWS

Dave,
<<"The contacts make and break OK, there's just no current flowing between the blue live feed and the switch contacts. They seem to be connected by a thin strip of brass which is concealed under the bakelite structure of the assembly. Does the plastic assembly come to bits? All the brass connections appear to be riveted on.">>

The blue live feed into the switch must be working as you say that dipped beam works. The blue /white wire must also be connected as you say that the high beam flasher works. The blue/white wire is connected to a knurled over brass rivet. What you see is the end of a long rivet which goes through the plastic (bakelite?)switch body and connects to the spring brass strips carrying the contact buttons. That long rivet is the only "concealed" part of the circuit and you know it is working as your high beam flasher works. That pretty well only leaves those small brass spring strips and the button contacts which you can see by looking in at the side of the switch unit as you operate the stalk. It is easier to see if you remove the column switch, but leave its lead connected. Poking around at the contacts with a small screwdriver when the lights are on should get the main to work, even if only when your screwdriver blade completes the connection. Carefull bending of the brass spring strip should fix it.

The design fault is that unless you fit relays, those tiny button contacts are carrying around 10Amps, probably more, and the continual make and break causes pitting and corrosion of the surface which is where the use of a needle file helps! The other weak point is the connection between the ends of the knurled over brass rivetts which can work loose. On the aftermarket ones the brass is too brittle and tends to break away completely.

The switch can be dismantled but it is a bit of a last resort as you have to drill out the main pivot pin which cannot then be repaired. I have done one by replacing this with a long BA screw but it wasn't ideal.

If you are working on your own prop a mirror up in front of the car so you can see what the lights are doing as you fiddle with the live switch.
Guy

LOL Guy - but, he's going to have to do all that anyway ;)! So I don't feel guilty about him not trying anything ...!!!

OK - it's possibly not the best, and, as such, if you e-mail me through your address, then I'll send it in the post, and, if it works, then great - if it doesn't, I'm certainly not going to charge anything - so all's well and good!

My e-mail is rachel-macbathotmaildotco.uk

And you DO need relays :)
rachmacb

Rach;- You have mail.

Guy;- As you rightly say, the blue live is working. However, the blue white is not connecting. The high beam flasher only works because it's energized by the live purple. I can only think that the fault lies in the long rivet that you refer to. I take your point about the button contacts wearing out, as the static contact is worn down to the level of its holder (although the moving contact still touches it)

I suppose I've got nothing to lose trying to drill out the centre pivot and trying to repair it as you suggested.

Thanks,

Dave
D MATTHEWS

With standard lights (55W) the original Lucas stalk switches seem to last around 30 to 35 years withot relays, which is not bad. Although presumably it would depend on how much night driving you do.

My first set went bad only after I installed some higher wattage bulbs. Two aftermarket replacement sets lasted barely 18 months each. I then repaired the original switch and put that back in but added relays and this seems to have solved the problems. My take on it is that relays are not necessary with the original switches, but are if you add extra lights or use higher wattage bulbs, or if you are using one of the lower quality replacement switches.
Guy

This thread was discussed between 03/11/2011 and 11/11/2011

MG Midget and Sprite Technical index

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