front headlight

Technical MGB discussion
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Posts: 29
Joined: Thu Jul 18, 2019 9:34 am
Forename: Mario
Surname: Sciriha
Location: Malta

front headlight

Post by Mario60 » Thu Feb 06, 2020 7:17 pm

I need your help.
I have the front driver side hesd lamp not working. At first i thaught that it is a burnt lamp and replaced with a new one. It still did not work snd checkef the fuses and they are ok. The high beam works fine. Any idea what the fault could be. Many thanks in advance.

Mario Sciriha
1972 MGB roadster
1971 MGB GT (for restoration)
1979 Honda CB650Z
1975 Kawasaki S1C 250
1974 Suzuki GT380
1979 Suzuki TS125
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Tom Brearley
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Forename: Tom
Surname: Brearley

Re: front headlight

Post by Tom Brearley » Thu Feb 06, 2020 9:11 pm

Hi Mario

It sounds like you have a bad connection somewhere. It might be dirty, rusty or loose. Since the passenger side headlight is working, the problem is likely located in the bundle of bullet connectors down by the driver's side horn behind the grill. It's the blue and red wires you need to focus on. A clear wiring diagram for your year of car can be found here:

It may be obvious when you inspect it where the problem is. If not, testing with a test lamp or multimeter should locate it.

I hope you achieve enlightenment.
1973 MGB GT (currently shaking down after 3 years off the road)
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Charles Farran
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Forename: Charles
Surname: Farran
Location: Warwickshire

Re: front headlight

Post by Charles Farran » Thu Feb 06, 2020 11:07 pm

Provided the headlamp wiring has not been modified from the original factory wiring, then the low beam headlight filaments are fed by the main loom down the inside wing.There should be a blue & red wire that goes into a double bullet connector behind the front grill. Two separate blue & red wires come out from the other side of the connector, one of which then feeds the driver's side bulb socket, the other one goes behind the grill to the passenger side & meets a single bullet connector, which then feeds another single blue & red wire that feeds the passenger side bulb socket. ( A similar arrangement applies to the high beam headlight filaments but in this case the wire is blue / white).

From the symptoms you describe, provided the replacement bulb has both filaments working, then you will probably have a poor connection at one of the bullet connections. These are notorious for corrosion due to where they are & hence the electrical circuit brakes down. The earth feed is the black wire & as the main beams work both sides & is the same for both sides of the car,a break in this side of things will not be the cause of your problem.

I assume that there are no breaks in the connector wire to the connector that slots onto the back of the headlight bulb.

You may find it worthwhile replacing the female bullet connectors altogether as they are easily done, whilst the same time cleaning all the bullets.

When pushing back together use a trace of vaseline or suitable dielectric grease to mininise / slow down future corrosion / break down in conductivity.
1980 Roadster
Vic Butler
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Forename: Vic
Surname: Butler
Location: North West Hampshire

Re: front headlight

Post by Vic Butler » Fri Feb 07, 2020 8:57 pm

Check the connectors in the plastic plug that fits on to the bulb. I've found that the contacts inside can get a coating of a verdigris looking substance.
I use electrical switch cleaner. It works wonders. You should be able to get it from electrical retailers.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
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