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MG MGB Technical - electrical problem

Hi Guys&Gals
I've been out for a spin in my 68 roadster, beautiful sunshine :)
when I got back I decided to check the car over and found the nearside indicator is lighting as well as the brake light when the brakes are applied and reducing the brightness in the brake light.
The offside is perfect, am I right in thinking this is an earth problem? if so where to look
Cheers Pete
PJ Thompson

Yes, it does sound like an earth problem.

The rear lamps are supposed to earth where they touch the bodywork, but it you have lots of lovely paint, they struggle to.

It might be worth adding some additional earth/ground wires to the rear lights from one of the mounting studs to the black wire in the rear loom.

There should be a ground return from the reverse lights. I can't remember if there is one from the number plate lights, or if there is even an earthing point in the boot, and I can't check in my boot as the car is upside down at the moment.
Dave O'Neill2

cheers Dave
do the lamps earth through the three studs and nuts that hold the bases to the body? I will check them tomorrow.
I think adding an earth wire from one of the studs on each lamp base as you've suggested sound like a better solution.
Regards Pete
PJ Thompson

firstly well done for using a B this time of year! and a roadster! and an earlier roadster too!

this will of course be frown on by the old farts but I wont tell them if you don't

as it's simple to do I'd also suggest you check the light unit as well as its earthing to body

disconnect and remove the light unit as a whole, clean bullet connects and bullets as required

remove the lenses covers from the unit and see if there's any crud on the front and clean as required

when you remove the bulbs note which way the offset bayonet goes on the brake/rear bulb

note - only clean the shiny bulb reflectors with a damp then dry cloths

clean off any crud from bulb metal bases and bulb holders, wipe glass of bulbs with damp then dry cloths

then check the rear of the lamp unit for crud and clean as required particularly at earth points, check lamp aperture on car body for rust/crud and clean as required

reassemble careful to put brake/rear bulb in correctly and not to over tighten lenses to base unit, you might want to use electrical contact grease on wire bullet connectors to keep damp and crud out
Nigel Atkins

Thanks Nigel
Where exactly does the light unit connect with the body? it looks as if the foam seals insulate the unit from the body.
Everything is very clean. its a new shell freshly painted
Regards Pete
PJ Thompson

As the shell is freshly painted I'd buy some small ring connectors, solder a length of black wire to it and put the ring between the body and the nut (on the stud). Even better if you can find another nut so you can fit the unit, then the ring and then the second nut. If you do this both both sides and the number plate lights (cant remember how an early set is fitted) then run the black wires to a chosen (hidden)site that can be prepared back to bare metal and then repainted.
Michael Beswick

Hi Michael
I will be doing exactly that tomorrow, I've got the nuts, ring connectors and cable
Regards Pete
PJ Thompson

the light unit is held to the body by three captive screw threads, one at the top and two near the bottom, these go through the gasket and earth the unit to the body, they're held by fasteners screwed on to them

just cleaning up these captive screw threads, fasteners and importantly your painted body could solve your problem as it may be the fresh paint is preventing a good earth connection

might just be me but personally I'd not bother with more earth leads just make good what earth connections you should have and add electric connection grease

you could add a star washer (external serrated) to under each faster, the type of washer that looks like a cog that bites into the metal to give more connection and help prevent the fastener coming loose you then protect each connection - battery post spray, electrical connection grease, etc.

all electric wires and connections need to be clean, secure and protected
Nigel Atkins

Thanks Nigel Dave Michael
for your replies ill let you know how I get on tomorrow
Regards Pete
PJ Thompson

There should be a black ground wire from the lamp base to the harness.
Art Pearse

Sorry, thought I was on the MGA board!
Art Pearse

Art, you are partly correct, because there should have been!
Dave O'Neill2

The rear light clusters earth through the physical fixings to the back of the wing panel. These don't usually give problems as there are three of them and the boot is a relatively benign environment. It's a wonder the front light clusters don't have more problems, given that they are bombarded with water, dirt and originally at least, salt.

Reversing lights have earth wires, there should be bullets behind the rear panel nearby.

Chrome bumper number plate lights didn't have earth wires, I had to provide them as mine didn't light at all after restoration as the earth path is bulb - holder - housing - overrider - overrider bolt - bumper - bumper iron - chassis rail. Rubber bumper number plate lights should have earth wires.

All the earth wires plus two for the tank sender (bar later models) and fuel pump go to one of the number-plate fixing bolts.
Paul Hunt

Hi Guys
I've fixed the problem using a cable off one of the studs on each lamp base to a bolt on the boot locking hoop. didn't really want to scratch any paint off the body
Lights are now perfect thanks

PJ Thompson

fair enough

thanks for reporting back
Nigel Atkins

This thread was discussed between 30/11/2013 and 01/12/2013

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