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MG MGB Technical - Need urgen t help with headlight switch

I am in a bit of a pickle right now. Received my replacement headlight switch yesterday. I replaced this once before a couple of years ago. At the time one of the three wires was not connected and I installed the new one using the same wires. Now I have to replace it again and not sure which one was not connected!.

My B is a US 74. Here is the senario:

Brown X X Red/Green


X Blue

If I hook all wires up this way I have headlights but no tail/side lights

If I reverse the Red/Green with the Blue I have tail/side lights but no head lights.

Really need to get this fixed today as I am call after midnight tonight

Thanks
GG Ginty

The switch makes the following interconnections:

In the 'off' position all terminals are isolated.

In the first 'on' position two spades are connected together, brown (12v supply) and red/green (parking lights) wires should go on these, it doesn't matter which way round.

In the second 'on' position all three terminals are connected together, so the blue (headlights) wire goes on the remaining spade.

If your switch does anything other than this it is incorrect or faulty.

If any one of the three wires is not connected then you will either get no lights at all (if it is the brown), no parking/tail lights (red/green), or no headlights (blue).

Are you sure you are trying the switch in all three positions? Or only two?

Paul Hunt

Thanks Paul.. I am trying in all positions.

I have it wired per the wiring schema for a 74 US B.

blue 1
brown 2
red/green 3

In this setup I have tail/side lights and no headlights. If I swop 1 and 3 around then I have the reverse, headlights and no tail/side lights. It seems that what ever is in plugged into 1 does not work. I am sure that it nothing at all to do with the wire connections etc. If I jump the brown and blue with the switch off I get lights. Perhaps a faulty switch?
GG Ginty

GG,
Use a multimeter to check for continuity through the new switch in each of the positions to ensure it has the correct configuration. I have had 2 headlight switches for 73/74 cars that were either incorrectly boxed or were built for another application and had the headlight rocker installed. Both were replaced with an apology from the supplier.

Dennis
D J Broad

Sounds like it isn't joining the third spade to the other two in the third position i.e. the second 'on' position. In which case a faulty switch.
Paul Hunt

It sounds like the new switch only has one "on" position. Not sure how the original or the second switch ever worked properly if one of the wires was disconnected. It may be that they were not the correct off -on -all on rocker.
Do you still have the original switch? Maybe the disconnected wire was the culprit all along.
I just had problems with my headlight switch, and it turned out to be gummed up contacts inside the switch.

Pat
Patrick Callan

This thread was discussed between 09/10/2009 and 10/10/2009

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