Electrical Fault

i have a 78 mgb roadster and noticed today that the front passenger side headlight, passenger side rear light and rear passenger number plate light are not working, however main beam is ok as is rear brake light on the same side. If anyone could give me any advice as to what might be the cause of the problem it would be very much appreciated.

There is a bundle of bullet connectors in front of the radiator near the headlight that can get corroded and can affect the rear lamps. Try cleaning those up.
-David

What David said. I had a headlight that the low beam would go out periodically and them come back for no reason. I cleaned all the bullets in the front and everything seems to be working well.

Here is a link for a color-coded wiring diagram. It even shows the bullet connectors.

http://www.advanceautowire.com/mgb.pdf

If you look on sheet 25, you will see that the right side Tail, Rear Marker, License Plate, Front Parking & Side Marker Lights share the same fuse (the second one). If any one of these lights is working, then it is not the fuse.

The only thing the headlight shares with those lights is the headlight switch. If the switch was bad, you would have more stuff not working.

I would conclude that the outages are separate and should be investigated separately. Get yourself a 12V test light and probe the suspect bullet connectors and lamp sockets first.

The headlight may just be burnt out. It would be a good excuse to replace those old headlights with new halogen units. A nice, cheap upgrade especially when you consider that all lamps lose lumen output as they age.

The side marker lamp sockets and the license plate lamp terminals also have a tendancy to get corroded.

Clean what you can with a scotchbrite pad and coat with dielectric grease.

Oops, my bad. Your passenger side and my passenger side are different. The left marker/tail lights circuit would be the first fuse. It also looks like the correct wiring diagram would be sheet 33.

And know that the rubber covered connector "tubes" used in Lucas wiring harnesses to connect the "bullet" connector terminals on the wires are NOTORIOUS for simply crumbling apart inside from corrosion. You may find that you will need to get some new ones if the old ones have fallen apart on you.

thanks Bob,will i need to disconnect the battery while i do this ?

I always discnnect the battery. Too many things to go wrong on a 45 year old car!

thanks David will try that

thanks Bob sure worth a try

Thanks for info Keith, I will investigate now i have an idea of what im looking for