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MG MGB Technical - Full Beam flasher not working - HELP!!!

Hi Guys

Here's the problem.

I have a '74 BGT and the main beam flasher doesn't work on the drivers side headlamp.

It is very slow to respond and very dim. When the connections are switched around so that full beam is on and the flasher is then the dipped beam, it works fine!!

We have changed the bulb and rewired the headlight and it is still not working.

Also when we remove the fuses in the box one by one the headlights do not go off.

How are the headlights fused and does anyone know what couls be causeing the malfunction with the flasher??

We have even switched the lamps and it is only the drivers side that there is a fault with. we have also re-earthed the lamp - still no joy.

Really scratching our heads now as we are at a loss to what is wrong.

It is only the drivers side - not the nearside which is the main headlight.

All help is greatly appreciated.

Lucas is the Prince of Darkness - believe me!!!

Adam
A J Cooper

I also forgot to mention that when the engine isn't running the brake light and indicator on the drivers side are slow to respond.

This may be relevent as it is only the drivers side that is affected.

When the engine is running the rear lights work fine

Very puzzling!!!!

Adam
A J Cooper

Adam, The headlamps were not factory fused, so they're not fused unless someone has added fuses. Have you made some voltage measurements at each light? Has the light been rewired with something other than the correct size wiring? Good luck, Clifton
Clifton Gordon

Check all the grounds. A dim headlight is an indication of a bad ground or it can be a bad connection somewhere. Remove all the connectors and reinsert. Oxidation takes its toll on electrical connections. I use a light coating of anti-seize on all connectors. Prior to antiseize I used havy grease which also worked well but it does dry out.
Mike Magee

Just for clarification the headlamp flasher uses the purple fused supply from 69 on, unlike the main lighting switch which isn't fused.

If the brake light and flasher are slow one side it is probably bad grounding on the rear light cluster that side, but that shouldn't affect the headlamp flashing. There is no ground wire on the rear light clusters of any year, they just rely on the mechanical fixings, like the chrome bumper front flasher/parking light unit.

It's not clear whether the main and dipped beams when powered from the main lighting switch are working correctly. If they are, and it is only the drivers light from the flasher that doesn't work properly, then I shall have to think about that a bit longer, and my first thought would be non-standard wiring. Normally everything from the dip/flasher switch out through the headlights and to ground is common to both flashing and normal lighting.

If the main beam *is* similarly affected then look to the 4-way bullet connector in the blue/white wires by the right-hand headlight. Take some voltage measurements on the drivers-side wiring with the headlamp flasher pulled, you should see 12v on the blue/white and 0v on the black. Less than 12v shows bad connections back towards the flasher switch, and if only the one headlamp is dim it must be in that bullet connector, more than 0v on the black ditto. If those are the voltages you get but the lamp is still dim then check again in the actual bulb holder.
Paul Hunt

Paul, this is how it is!!

We switch the headlights on, near side works perfect - flash the headlights and it flashes main bean. Drivers side however seems to dim and is slow to react.

The only thing is, we have rewired the drivers side so that rules out degraded wiring inbetween the headlights and if it was anything further up (i.e. above the new wiring then surely both headlights would be affected. We even switched the lamps around but it was still dim, which rules out the unit and the bulb.

When we switch the dipped and main beam plugs on the rear of the lamp it works perfect but in reverse. i.e. main beam is on when headlights are on and when we flash it dips.

We are really stuck as to what it could be!!

cheers for your help!!
Adam
A J Cooper

Oh, and by the way, we have stripped and cleaned all the relevant switches so it can't be them.

Even so if it was the switches surely both headlights would be affected not just the Drivers side.

My head is starting to hurt with this one!!!!!!
A J Cooper

Hi.

Adam, I suggest you re-read Paul's response, it seems almost certain to be the connector in the front loom or the wire beween the lamp and that connector.

Don
Don

Hi,

I recently had a problem very similar to this (but both lights) and I found it to actually be a 4 way connector near the lights.

I had rewired all the lights after the problem started but still got the same problem. I had replaced all the wires and heads but not the actual connectors, just cleaned them. After replacing the connectors it was fixed and then other problems arose, so I rewired the grounds from start to finish, leaving no joining wire untouched and yay, it worked.

Admittedly, I have lost my high beam again so I still have to chase it. But what I am trying to say is that even repaired connections are bunged due to the old stuff they fit into.

I used to blame the evil Lucas but admittedly, the wiring is 40 years old. It has lasted damn well for 40 years.

Cheers,


Ad
AJ Hooker

We have found out that there is a power shortage at the end of the wiring loom for towards the headlights - cheers Paul - ur plan worked - we tested the voltage ar the point where we had re-wired the drivers headlight. This means the problem is further between the switches and the join!!

we have come up with a plan which means we don't have to re-wire the whole lights system!!!

My dad has gone to the car wholesalers today to get two power relays.

Where we have rewired the drivers side headlight on the main wiring loom in the engine bay we are going to install the power relays.

The power is going to come from the starter motor, which is connected direct to the battery.

The relays will then supply the power for the headlights.

I think my dad is a genius - do you think that will solve the problem???

Adam
A J Cooper

Adam - it may do, but by getting round the problem not fixing it. Personally I don't like doing that, it is quite likely to get worse and eventually may not even operate the relay. Fitting relays *is* a good idea particularly if you have uprated lights as it does get full voltage to the lights themselves and takes a lot of current out of the switches and the several connectors en route. But I recommend fitting fuses as well as relays, one per filament between the relay contacts and light units, and a main fuse between a brown 12v supply and the relays. And if you fit relays between thre switches and the 4-way bullet connector which is the normal position it probably isn't going to completely solve your problems anyway.

There are several things in your posts which are still not clear - for example you don't say what happens when you use the dip-switch to go between main and dipped beams, only what happens when you have dipped beams on *and* use the flasher. That scenario puts all four filaments on which doubles the current through the ground circuits. It is possible that this is giving up when faced with so much current. Even so it would have to be at the four-way bullet connectors by the right-hand headlight to only affect one side. Is the right-hand headlight going dim with both filaments on i.e. is the dipped beam going dim as well as the main beam not glowing at full brightness? If so you have a ground problem, either at the headlight or the 4-way bullet connectors I keep coming back to.

I also suspect you have more than one problem, which is helping to confuse things.

Paul Hunt

Paul you are an absolute star!!

My dad has been on the problem all day and has solved it, he thinks!!!

He has rewired the headlights using relays and fuses.

It was the connector like you said and after two hours of searching he has also found the dodgy earth.

Is working fine now.

Thank you so much for your help.

King of MG Wizards that you are!!

Adam
A J Cooper

My pleasure ...
Paul Hunt

This thread was discussed between 29/02/2004 and 02/03/2004

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