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MG MGB Technical - headlights go out when i indicate

hi guys, i have a 68 gt (with 73 wiring, long story) and ive been driving it fine for 2 years and now whenever i indicate right, the headlights go out. then the lights come back on when i turn the right indicator off. Then if i indicate left, the headlights stay on until i turn the indicator off again and the lights go out. its so weird!! Any ideas?
A P New

Does it happen on both main beam and dip?
Dave O'Neill 2

just dip
A P New

I'd be inclined to have a look at the terminals in the dip switch. As it has '73 wiring, I'm assuming you have the dip switch on the column stalk rather than on the floor?
Dave O'Neill 2

yeah thats right, everything electrical is 73 (previous owner prefered the later dash). as its sunny out ill have a look and report back
A P New

The dip switch can be removed and cleaned up. You can also just remove the plastic covers and leave the wiring harness connected and check the contacts. Watch closely if you remove the switch and open it up since the springs will likely eject like an aircraft seat. There are 3 or 4 of them the size of springs you might have encountered in a retractable ball point pen along with a small metal cylinder. There should be three contact "poles" that connect and disconnect when the stalk is moved forward for high beam and used for "dip to pass". They're visible without opening up the dipswitch mechanism, made from tempered metal and the tavel is a fraction of an inch so wear and loss of tension apply with aging. However, before you open up the dip switch, check your lowest fuse and holder in the fuse block. The fuse may test OK, but the lowest block (brown on one side) can make for interesting results if the fuse is a little loose. I had similar symptoms and found it to be the fuse. It's possible that's your entire problem. If needed you can also replace the dip switch completely. There is a manufacturer of new ones that I've seen on E-Bay.
Rick Penland

There are no fuses in the headlight circuit (except headlamp flasher) which come of the brown circuit whereas the indicators are off the green and different earths so no commonality in circuit either. Must be the later column switch, as originally on a 68 the lighting, dip and indicator switches were all feet apart!

As the problem is affecting the dipped headlights not the flasher which flashes the main beam it'll be the column dip-switch, the contacts not having enough 'follow-through', possibly a weak spring or stiff mechanism for snapping between dip and main so that they are just opening when you move the stalk for the indicators. This, for example, is for a 73 http://www.mgb-stuff.org.uk/dip.htm
PaulH Solihull

Hope ok to dip in this thread re headlights - I have a situation where my headlights are on constantly - is required by law for new cars here in DK. The PO did the same for the car. Would like to be able to turn off/on but do not know where to start re: wiring -any advice?
/Moss
Moss

Moss

What year is your car?
Dave O'Neill 2

1977 roadster LHD 4 syncro non od...
Moss

As it is a PO mod (presumably) it will all depends where the PO took the power from to light them independently of the main lighting switch and how he wired them.

Presumably they only come on with the ignition, if so they must come off a white, white/brown (assuming 77 with ignition relay) or green somewhere. White/brown at the fusebox would be the most logical and sensible as that comes off the ignition relay. Whatever the source that could go to the white/red for the dipped (presumably) beams, and the most sensible place for this would be at the bullets by the right-hand headlight, but could be inside the cabin at the dip-switch connections. But it also depends on what the dip-switch does now - if that does its normal job of switching power from the dipped beans to the main beams i.e. the dipped beams go out on main beam, then instead of going to the blue/red the ignition feed will be to the blue wire that goes from the main lighting switch to the dip switch. And does it still have a main lighting switch? It could have been removed, the ignition feed to the dip switch taking its place. What happens with the rear and parking lights at the moment? I.e. do they also come on with the ignition, or are they manual?

PaulH Solihull

For 'white/red' above, read blue/red.
Dave O'Neill 2

Paul, both headlights, parking lights and rear lights are turned on with the ignition. The high beam is turned on by the stalk on the left hand side on the steering column. The switch for turning on the lights on the steering column, left hand side, does not function anymore.
/Moss
Moss

Moss,

I would be curious if the high beam comes on and the dipped beam stays on with the way your car is wired. If so, you are pulling a lot of current.

Grab the wiring diagrams from Advance Autowire http://www.advanceautowire.com/indexb.htm and download the pdf with the wiring diagrams in it. You should be able to rewire your car correctly using the information.

warmly,
dave
Dave Braun

Thanks Dave, pdf downloaded - a bit of reading to do - with a dictionary then...the dip and main beam do not stay on same time - either or.
/Moss
Moss

I would guess that you have an ignition feed - either white or green - connected to both the red and blue wires which would have originally been connected to the headlamp switch.

If you remove the steering column cowl and look at the headlamp switch, you will hopefully see what has been disconnected/rewired.
Dave O'Neill 2

Hopefully said ignition feed to red and blue (see below) is via a relay, or that is putting an awful lot of extra current through the ignition switch, and the green circuit fuse if it is from a green (take the 2nd fuse up out with the ignition on and see if the lights go out).

If to the blue then the dip switch will be disconnecting the dipped beams when the main beams are turned on by pushing the stalk away from you. If the dipped beams stay on when you do this, then the ignition source is wired to the red and blue/red (not white/red as I said earlier and pointed out by one Dave) which would be pulling a lot of current as the other Dave has mentioned.

I'd expect the dipped beams to stay on if you pull the stalk towards you for the headlamp flasher, that is common to all MGBs.

Unfortunately whilst any official schematic is going to show you how they *should* be wired, it won't show how they have actually been wired or what two or more wires have been bridged and/or cut or where that has been done.

If the main light switch still causes the lights to come on when the ignition is off, then it could be as simple as a bridge between the white at the ignition switch and the blue and red at the main lighting switch. However if the main lighting switch does nothing when the ignition is off, then wires have been cut and rerouted.
PaulH Solihull

If the light switch still works as intened without the ignition being on, turning on the lights at the switch would also make the ignition circuit live, if there was a bridge between the white at the ignition switch and the blue and red.
Dave O'Neill 2

well i finally got round to taking the indicator stalk apart and found that the blue/red wire had snapped off the crimp. I indicate one way and the wire is moved away from the contact, i indicate other way and it touches. so it looks like ill either have to solder it on (which wont be strong) or get another indicator assembly. Oh the joys of classic motoring lol.
A P New

"If the light switch still works as intened without the ignition being on, turning on the lights at the switch would also make the ignition circuit live, if there was a bridge between the white at the ignition switch and the blue and red."

Very true!

I soldered a wire to my 73 indicator/dip switch that had broken off but it wasn't very successful. Ended up buying a new switch - expensive!
PaulH Solihull

This thread was discussed between 27/02/2011 and 11/03/2011

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