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MG MGB Technical - headlamps - different brightness

On my 70 B, the right headlamp is bright, but the left is much dimmer. The highbeams are ok, and the flash switch. Both lamps are brand new. One strange wiring situation though. I have a blue/red wire, blue/white wire, and just blue wire. Currently i have them hooked up using the blue/white and blue and of course ground. The wiring diagram shows to use the blue/red instead of the blue, but it also doesn't show a blue wire.

Any help is appreciated, this is all i need to get the car to pass it's safety.

Thanks

Ken
70 B
Ken Harris

Try the earths , they a Black , One my RHD car the LH is run back to a double bullet connector next to the Rh lamp and then to ground ..You are correct that main amd dip are Bl/Wh Bl red in the diagram
S Best

Ken
Almost certainly an earth problem check back along the lead for breaks and a good connection at the earthing point

Colin
C J Bryan

Just a possibility, but my '69 had the high beams and low beams crossed. One headlight would flash high and the other would be low. Wires were crossed. I blamed the DPO but I was scratching my head for a couple of days.
Luigi

Something has been changed. The wires are UW, UR, B(lack) (ground). THe only blUe is from the light switch to the dimmer switch = lighting main power. After the dimmer sw are only UW & UR. The dim light is almost certainly a bad ground.
FRM
http://www.usachoice.net/gofanu
FR Millmore

Since both his high beams are good, that kinda says the grounds are OK. Possibly a bad connector where the two low beam wires split in the harness? Sounds like someone may have replace his UR wire with a plain blue one and the connection is poor where it joins the harness..
R. L Carleen

Bad ground is the first thing that jumps out when one thinks of headlights that are difering brightness, but when troubleshooting that problem on our MGB, I found that it was the 12 volt supply that ws the problem. All the headlight wires come together just off center under the shelf that has the hood latch mounted on it (I have seen it called the slam shelf) and it was there that I found one of the bullet connectors had developed corrosion and overheated, causing a high resistance path to one of the headlights. I don't recall if it was the high or low beams that were affected, but I redid all the connectors at that point. Both headlights are the same brightness now. Good luck - Dave
David DuBois

I had the same experience as David DuBois. Try cleaning all the terminals, esp. in the socket AND on the bulbs with a small wire brush on a Dremel rotary tool. I have solved a number of these "mysteries" by cleaning the contacts. This solved a situation where one of my rear turn signals didn't work, despite the connections tracing out just fine with a voltmeter.

Also, I recently replaced both the generator and the voltage regulator on my TD. Yet, the battery was still not charging. After confirming that the generator was working, I cleaned the contacts again on the regulator. It still didn't work. I then sprayed contact cleaner on all the contacts, and voila!, everything worked. It seems that a small grain of sand from the emery paper was blocking one contact!

So try both the Dremel technique and electronic contact cleaner (spray) first before anything else. Then follow up by looking at grounds, then wiring leads.

Best of luck,

Ira
Ira Spector (PA)

Yes on the ground, but also check the connector socket that attaches to the lamp.

A bit of dirt or broken metal tang inside the socket may be a problem.

It's a simple problem with a simple fix.
glg

As an added note, when you clean the bullet connectors, consider changing them to the Posi Lock connectors <http://www.posi-lock.com/>. these are a much more positive connection for the wiring. If you continue with the original bullet and sleeve connectors, get some dielecric grease and put a shot in each connector and then follow up with a glob of it around the wire where it enters the sleeve. This will keep the moisture out of the connector. I also do not want to detract from checking and cleaning the ground points (even if it doesn't cure the problem, it will keep future problems from developing. See my article on ground point preparation <http://www.omgtr.ca/technical/General%20Technical/grounding.htm>
for how the ground points should be preped. Cheers - Dave
David DuBois

This thread was discussed between 04/06/2004 and 05/06/2004

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