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MG MGB Technical - One headlight brighter

My left headlight (72 B USA) is much dimmer than the right, even after replacing the headlamp, and checking conections. Also the high beams only work on the right side; the left side remains at the same lumen output.
William

William - Could it be that your left headlight is point at the ground, or up at the trees? I see a lot of older cars that have that problem. From inside the car and even for oncoming cars, it looks like a dim bulb, when the only thing wrong it that it is pointing in the wrong direction. Another possibility, the plug that fits onthe bulb may be wired incorrectly. That happened on our MGB and I finally noticed that there was no difference in high or low from the right bulb. Like you, all the connections and grounds were good and even a new bulb didn't fix the problem. I started poking around with a multimeter and found that somehow the plug had been hooked up incorrectly. Changed the wires and both headlight looked the same. Good luck - Dave
David DuBois

William

Had a similar problem on my motor caravan (RV to you 'mericans). Checked bulb by substitution - OK, checked connections - OK, then ran an extra temporary earth to the chassis - hey presto problem solved! Obviously the original earth wire itself was "bad" so a permanent new earth lead was wired in.

Laurie Webb
75 BGT V8 Teal Blue
77 BGT 1950cc
88 Talbot Express homebuilt motor caravan (RV)
L Webb

The left headlight uses the bullet connectors by the right headlight as well as its own so both sets need to be cleaned and checked. If the output is noticeably dim and doesn't change from dip to main then I suspect the ground is missing altogether and so the two filaments are glowing in series. I've also had a headlamp problem where the short loom between the connectors and the bowl had cracked insulation in one wire, which eventually led to the copper strands corroding through and failure of one beam. This took a bit of finding and I could have thrown an extra wire in and got round it, but I persevered and found the real problem :-> Also when checking connections with a voltmeter you must do so with everything connected as normal and the fault i.e. lamp out evident. With no load on the circuit a voltmeter will 'see' a full 12v even though a very bad connection, way too bad to allow a lamp load to work.
Paul Hunt

add to Paul...I had one where a body guy had ripped the wires out of the plastic connectors and replaced them wrong so I got lights going different directions...one bright, one dim. You could also have wire broken inside the connector. I had one with wire broken inside the insulation up close to light unit.
J.T. Bamford

This thread was discussed on 22/10/2004

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