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MG MGB Technical - Lovely Lucas Electrics

I have just finished a fairly extensive renovation of the body work of my '72 B and can not get the lights to work correctly working from the trunk. The headlights are fine so are the indicators & reverse lamps but only the driver side rear light comes on. Is there a suggested sequence I should use to figure out where there might be a short? I think the electrics have beeb tinkered with before.....but all the lights used to work......
Stephen Lewis

First, have you taken a simple test light or meter and checked if the light(s) is getting power. If the left light is working and the right is not, it sounds like it may be the socket or the ground on the right light. With the MGB wiring, the ground wire is always a good place to start checking, especially since everything else is working in the back of the car. Also try hooking up the wires on the side that is working to the other side to check the bulbs and sockets. Also, does the brake light work on the drivers side?
Robert Browning

Stephen....check your ground in the boot where it most likely connects to the license plate bolts....Clean that area and reconnect....rick
rick ingram

Another place to check is the top two fuses in the fuse box and the wires connecting to the box.
Charles Ake

Thanks for the advise, I have checked everything you have mentioned here but there is something still not working. The strange thing is that it worked briefly but I never found out why. It seems that the electics may be grounding to the body and not through the black wires as it is supposed to do???
Stephen Lewis

It is unlikely you have a "short". If you did, none of the rear lights would work. So either are not getting 12 volts to the lamp, the lamp is bad, or the ground is not connected properly. With your extensive revovation comment, either is possible.

First determine if you are getting 12V to the lamp socket. If not, find the loose connection.

If you have 12V, recheck that the lamp is good and the ground wire is connected to a clean metal location.

Although unreliable, the circuit is actually simple.
John Smith

FYI:
Here is a very good site that may give you some info on how to assist your Lucas electrical system in becoming as reliable as any other make's. http://www.mgb.bc.ca/electrical

Rick is a true automotive electrical engineer as well as an MG enthusiast, and he has grappled with most of the things most of us have with the "Prince of Darkness"

Remember, the "Prince of Darkness has french, italian, german, and even american counterparts and they all rely on poor maintenance, often by a succession of DPOs, to keep them in power. (or out of it, as the case may be)
Bob Muenchausen

I would double and triple check the area that rick ingram mentioned. This is the most notorious reason for the failure of the rear lights imediately following a repaint. You may have to remove some of your new paint to ensure a good bare metal contact.
Andrew Blackley

The rear light clusters on all cars, and the front light clusters on CB cars, do *not* have a wired ground, they rely on the mechanical fixings. The number plate lights on CB cars are similar but the reverse lights do have a wired ground. So the repaint is obviously too good! I had to provide a wired ground to my number plate lights after as rebuild, and on a rewire of another car provided a wired ground from each cluster to the handy ground connector for each reverse light as a matter of course.
Paul Hunt

I just wired the rear of my car after a re-paint. For the tail lights, around one of the mounting stud areas, I took my dremmel and sanded off the paint inside the boot (trunk) to metal the size of the securing nut. I then took dilectric grease and put it on the bear metal and connected the nut. Excellent contact, no extra wires, and everything works great. I only had to do this once to each tail light.
Cris

To further Paul's point, the taillights are fastened (originally, anyway) with widebased stamped metal nuts with three sharp prongs. These prongs are what scrapes throught the paint and into steel to make a good ground contact, or three, for each lamp unit. If you don't have those, or the points are worn, external star washers are a good (or better) substitute for fastening taillights and front flasher/parking lamps.
Wade Keene

I cured my problem, I am still not sure why it cured it but I found that one the fuses was loose....duhhh. Copius amounts of WD40 and all lights are working except one front marker light, which I suspect is a connector behind the grill??
Stephen Lewis

This thread was discussed between 17/09/2003 and 21/09/2003

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