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MG MGB Technical - Main beam warning light

The main beam warning light on my '73 B is not 'showing'. Because the contact strips have disintegrated and are now unavailable I have soldered an earth wire to the bulb holder. With the bulb holder and black plastic light guide out of the speedo the bulb is working perfectly, but the light does not show when the assembly is pushed into position. I can see any reason why the bulb should go out, it is still on if I pull the assembly out of the speedo. Any suggestions please?
Graham Gilmore

Possibly something opaque is stuck in the holder. Can you see any light in through the lens if you hold the lighted bulb in front of the holder? -G.
Glenn G

Somehow I have cured the problem I did shine a torch into the hole of the speedo, but the main beam lamp did not glow. I then used a flexible rod to 'poke around' inside the speedo and then refitted the lamp assembly. Everything was then fine, but I did notice that the siting of the assembly has quite an influence on the brightness.
Graham Gilmore

If you can refer to the glow as 'Brightness' then you are on to a winner. I think most would call it dim! :)
Bernie
B Anderson

I replaced my instrument lights with halogen. The dials light up brilliantly, but I did not change the high beam light. Can barely tell it is even on.
Bruce Cunha

Bruce, can you give the spec. of the halogen bulbs that you used, make and part no. if possible. Try moving the high beam light tube around to see if you can improve the brightness, also check that there is a good earth. I soldered a wire to the bulb holder and then earthed it under the speedo retaining bracket knurled nut.
Graham Gilmore

I haven't looked inside the speedo for a long time, but it is true that many older Smiths instruments use bulb holders that double as light tunnels. The idea is to focus the light on the indicator lens while keeping it from over-lighting other parts of the instrument. If the holder is out of alignment with the lens, the indicator may be dim or dark when the light is on. One way to fix this is to insert the lighted bulb in the holder and slowly wiggle the holder in a circular pattern until the lens is lit. -G.
Glenn G

Hi Graham.

I picked up my bulbs from Jeff at Little British Car Company www.lbcarco.com.

71-000H
HALOGEN 12V 5W SCREW BASE INSTRUMENT/MAP LIGHT BULB
CVB - 12V FOR SMALL INSTRUMENTS WITH ONE BULB OR LARGE WITH TWO BULBS
Retail $25.29 Our Price $18.97

Not inexpensive, but wow do they light up my 67 GT instruments.
Bruce Cunha

Thanks for that Bruce, but I have not been able to locate those bulbs on the UK sites. I'll keep searching.
Graham Gilmore

The high beam indicator holder is indeed a tunneled 'focusing' holder type. If the 'aim' is slightly off, you won't see a thing (well barely in the best of cases).

To try and make sure it shows well, the holder is fairly rigidly held in place by metal clips on the back of the gauge body, which also double as the earthing path on one of them. Obviously these rust/break and the holder can come loose. Another thing to help is on the back of the gauge face itself; a small rubber tube/oring type affair that tries to hold the front end of the tube in place near the blue lense peice. These go brittle, break and crumble away in the course of 35+ years of the cars life and can let some of the light 'escape' around the edges. The gauge face can become loose in the body of the casing when the rear screws (or worse) become loose/break. This can also affect alignment of the tube holder if the face is sagging/moving in the housing and should be attempted to be re-affixed in a central position.

The above all equally applies to the Ign warning lamp on the tach, aside from the earth path of the holder, which should be insulated as the bulb is it's own earth path via the way the circuit works both ways to show of charging faults.

Rubber bumper cars do away with all this complexity by having simple tubes with coloured lenses on the ends of them in holes in the dashboard.

US spec cars can follow this up till about 67/68 when the dash changed and things your side got quite different.
RoadWarrior

This thread was discussed between 09/09/2012 and 14/09/2012

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