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MG MGB Technical - Dim headlights on a '79 B

Hi Everyone,

I'm helping my friend with this '79 B. The headlights and all other external lights are pretty dim. I've never had this problem on my MG's, but I went through his car and checked the grounds that I could find. I took apart the connections at the bullets and cleaned them. Is there something that I've missed here? When I turn the high beams on, the headlights are pretty bright.

Thanks in advance.

Dave Plantz

Are they old headlights, or newer halogens? They may just be that dim.
Jeff Schlemmer

Maybe a bad dimmer switch, do some voltage checks at the harness while flipping between high and low beams. RIC
R E L Lloyd

Hey guys,

I think the head lights are halogens. They look fairly new. Where do I check the voltage at and what kind of reading should I get on the meter?

The guy at the state inspection station told me that it was a bad ground at the battery or a missing ground strap on the engine. I've never heard of that, but could it be?

Dave Plantz

Dave. Check the voltage at various points in the system. The battery should put out about 12.0 to 12.5 volts. With the engine running, the alternator should be putting out 13.5 to 14.5 volts with the higher voltage being better. Just start checking voltages "along the way" from the brown wire input to the headlight switch, on through the input to the headlights, then, throug the headlights. Where you find your voltage drop is a place to examine and try to improve. Grounds, connectors and broken wires are what to look for.

On the rubber bumper cars, the ground strap is between the transmission crossmember and the transmission. If it is not connected, the car will not start. (Found this at 2 am when trying to get an engine into my daughter's car for a car show the next day. She took my GT for the show and we found the disconnected ground after the show was over and the pressure was off. All great fun.) Les
Les Bengtson

Hi Les,

I checked some voltages on that '79. At the battery, there's 12 volts. At the brown wire on the head light switch there's 12 volts. I lose this at the head lights, which are getting 8 volts. Would this be the dimmer switch? Also, I noticed that the high beams only work in the flash mode, and not the on all of the time mode. The switch doesn't feel loose. Any thoughts as to how to proceed?

Thanks in advance.

David Plantz

Dave. Pull the cowl. Do not remember if you can do it without pulling the steering wheel. Then, check voltages into the switch and through the switch. Also check for power out when the high beams are selected (stalk pushed forwards). If you show good voltage there, continue going forwards, following the wiring diagram, and check at the connector, etc. to see where you are loosing the current. You might also visit Paul Hunt's website, "The Pages of Bee and Vee" and drop him a line. He is much better at electrical things than I. Les
Les Bengtson

This thread was discussed between 12/05/2005 and 15/05/2005

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