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MG MGB Technical - 67 headlight puzzle

My low beam (dip) on the right side went out. I believed it to be the headlamp but learned I was wrong after installing a new one and it also did not have the low beam. High beam works fine. I pulled the tester out and find current to the low beam side of the headlight plug in when I pull the switch and find current to the high beam side when I use the floor dimmer. Now I am really confused. How can this be? Any thoughts?
Ralph

Hi Ralph.

Maybe the new unit is faulty, try a resistance check on it.

Don
Don

Ralph, I think you may have measured voltage rather than current, I assume you measured from the plug to ground and looked for 12 volts. The ground circuit should be ok as it's common to both filaments. I use a battery charger to check for faulty bulbs. It's quick, I would do that first. If the bulb is good check the the bullet connector where the low beam splits for a good connection to the right low beam filament. It may be corroded or loose and show a voltage but may not pass enough current to light the bulb. Just a thought, Clifton
Clifton Gordon

I'm with Clifford, you were probably measuring voltage. As Clifford suggested, check the bullet connector for corrosion (it is hidden under the horizontal panel that contains the hood latch mechanism and is just about directly under the latch). It is my bet that you will find corroaion un the connector as a minimum. On our MGB, I found that the corrosion had caused sufficient heat build up to make the insulation crisp about 2 inches back from the connector. With that situation, there will be 12 volts at the headlight plug if the bulb is not plugged in, but as soon as the bulb is plugged in and starts drawing current, all the voltage will be dropped at the corroded connector. I would suggest replacing the bullet connectors for both the high and low beam lines with Posi-Lock connectors <http://www.posi-lock.com/> for a permenant fix like I did. Good luck - Dave
David DuBois

Those are some cool looking connectors, David. Might have to check them out.
J.T. Bamford

JT - They are a bit pricy, but really work great. They even make a waterproof boot for them, although a dab of RTV around the wire entry will do the same thing cheaper.
Cheers - Dave
David DuBois

I would still try a new ground. Had a similar problem with low beams being yellow. Highs were fine. Corroded ground was the problem.
Bruce Cunha

If it's not fixed by now, take a look at the connections in the plug that attaches to the headlamp. It's not uncommon for the blades withing that plug to break or be corroded.

Then, of course, getting to play Lucas lamps or Carnegie Hall is just a matter of having the right and good connections -- all around.

We all have our own methodolgy, system in prioritizing any electrical troubleshooting. Study the wiring scematic diagram and check out all the stuff --- easy and obvious first (like a broken spade in the connector, all connections and work toward the more complicated stuff, -- like a switch.

It's really quite easy.
glg

This thread was discussed between 10/10/2004 and 13/10/2004

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