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MG MGB Technical - HI BEAM PIDIDDLE

My 1979 MGB left high beam does not light up. Replaced both headlamps and still no left high beam.

"Flashed" the stalk and only right high beam.

Switched on the lights and moved the lever to high beam position and no left high beam

Low beams are fine for both lights

All fuses appear to be fine.

As I am not too electrically inclined, I am armed with only a test light.

Any thoughts would be appreciated

Thanx in advance

cheers

Gary

79 MGB
gnhansen

Open-circuit/bad connection between the two clusters of connectors by the headlights in the blue/white wire. Or an open-circuit in the blue/white tail between the left-hand (facing forwards) connector and the bulb holder or connector (BT, DT although mine was the dipped beam).

With those connectors and their exposure to the weather it is best to pull them all, polish the bullets and replace the connectors, reassembling with Vaseline. When reassembling make sure the bullets are pushed all the way in to the metal sleeves of the connector, you meet resistance when about 3/4 the way in but you need to push harder to overcome that.

If that doesn't cure the problem then with the high beams switched on check for 12v with your test-lamp on both sides of the blue/white connector, touching the back of the bullet in the case of the tail to the headlight and not the sleeve. If that's OK go to the bulb holder/connector end of the tail and try there. If not at that end the conductor has probably corroded through inside the insulation of the tail due to damaged insulation, that was what happened to mine. That side just had the three wires, no overall sheathing, the new tail had the sheathing so better protected.
Paul Hunt

It could also just be the bulb or sealed beam that has died.
D Balkwill

D.Balkwill: I failed to mention that I did swap the headlamps to test for bulb failure. Sorry for the omission. Bulb failure is not the case here. Thank you for your input.

Paul H: Thanx again. Your diagnosis is spot on. I do indeed have wire failure from the Blue/White wire "bullet" connector to the headlamp. I did rig a test jumper from the "bullet" connector to the headlamp and the bulb did light up on high and low beam. So now I need to run a new lead from the "bullet" connector to the headlamp and I will good to go.

cheers

Gary

79 mgb
gnhansen

This thread was discussed on 09/07/2009

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