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I have a problem,well an electrical problem which is driving me bonkers.

the car will be fine for months then the headlights will not work,and even one right hand indicator repeater will light up,which as far as I know does not share any circuits to headlight wiring.

Have checked all earthing points I have found but beginning to think it could be faulty original light switch .

Don't understand the dark arts of electrics.

Can anyone help with advice what to check next.

Michael.

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On my '69 CP the headlights are on totally different circuits to the indicators from the 4 main fuses onwards.

Fuses look OK? Wiring connectors and switch terminals  look OK. Do the high beams work? Does the dimmer switch work? 

If it's an intermittent fault in the light switch it could be difficult to diagnose unless it happens while you have access to a multimeter in  which case you can start tracing the fault back from the headlights. 

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You should probably have one of these handy, just in case...

Good luck though. I'd be hunting for a dodgy earth as well. Can be an absolute pain to find.

John

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Dodgy earth is most likely cause, as has been said. Also check and clean all connectors in the affected circuits. 50 year old bullet and spade connectors can easily be corroded or lose their spring/grip, leading to intermittent faults.

Nigel

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11 hours ago, Mg haggerston said:

I have a problem,well an electrical problem which is driving me bonkers.

the car will be fine for months then the headlights will not work,and even one right hand indicator repeater will light up,which as far as I know does not share any circuits to headlight wiring.

Have checked all earthing points I have found but beginning to think it could be faulty original light switch .

Don't understand the dark arts of electrics.

Can anyone help with advice what to check next.

Michael.

Hi Michael,

have you got any electrical skill at all (continuity test etc).

Have you got a simple digital multimeter or a 12V bulb on a long fly lead.

If you have checked ALL the 12V supply connectors and ALL the earth connections then you will need to do voltage tests. However you will need the fault to be present.

If you are lucky enough to have the fault present while in the garage then starting at the affected bulb check the first connector for 12V - follow the wire back to source.

If you have 12V at the bulb then it must be the earth.  With 12V at the bulb check the first connector on the earth wire (assuming a chain) this voltage should be zero.

If there is a voltage then move down the chain or suspect that earth point.

Or -with the fault present connect a fly lead direct from the battery positive to the 12V on the bulb (as close to the bulb as possibe)

Do the same for the earth - fly lead from the battery negative.

 

Tedious but it works.

 

Roger

 

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If I have understood your description properly, occasionally your headlights do not light but instead the RHS wing-mounted  indicator repeater lamp lights. 

As you say, those circuits are completely separate as are the switches that operate them so it is odd indeed. 

There is one peculiar set of circumstances that can cause that to happen and as others have said it is an earth fault. It requires that the repeater light and the headlamps share a common earth path and that this point somehow becomes electrically disconnected from the chassis earth. The current from the headlamps will then pass through the repeater lamp and the other RHS indicator lamps, to find earth.  The headlights will not light and neither will the main indicator lamps but the repeater lamp may come on dimly because it is the lowest-wattage bulb in the chain. 

The diagram below shows current flow with orange arrows, top as it should be, below with no earth.

fault.jpg.3e7a0e12c6564cda2bb2d1189fa8a766.jpg

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If it happens in your garage you could make up a long jumper lead and run it from the headlight earth to the battery negative terminal- if the headlight then works you have earthing problems somewhere.

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Thanks for all advice its great to have a really helpful forum.

It does seem to be a earth fault somewhere? thanks Rob for the diagram that's seems to be problem.Roger my knowledge of muti meters involves switching it on I do have one but got as far checking the battery voltage with the mystic thing.

Could be a good idea for seminars at the international car electrics for dummies or where to put your probe?

Will spend tomorrow in the garage kicking the car.

many thanks Michael.

 

 

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Michael,

When making changes to my TR6 wiring the loom(s) are original. I was surprised that the black earth wires for the headlights /horn/ front sidelights terminated in a push connector in the centre of the front valance. At the same time I noticed that the earth wires for the instruments terminated in a push connector on the engine side of the front bulkhead under the steering column. The earth wires for rear lights /fuel pump etc terminated in a push connector in the boot near the N/S rear light. So the three separate earth circuits were not interconnected but relying on the connector and body panels to complete the circuit. I presume that after a rebuild and respray the body panels do not have electrical continuity as the better paintwork insulates the body panels from electrically interconnecting.

I fitted a length of 70Amp black earth cable (less than five metres) to interconnect all the separate earth looms and also connected midway to the engine earth cable near the wiper motor. Cost - less than a fiver took a couple of hours.

Afterwards I have had no issues with electrics and the headlights are noticeably brighter. 

As a start I would locate the front earth connector on the front valance and measure the resistance between that connector and the braided earth on the battery.

 

Alan

Edited by barkerwilliams
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On 10/3/2020 at 7:20 PM, Mg haggerston said:

Thanks for all advice its great to have a really helpful forum.

It does seem to be a earth fault somewhere? thanks Rob for the diagram that's seems to be problem.Roger my knowledge of muti meters involves switching it on I do have one but got as far checking the battery voltage with the mystic thing.

Could be a good idea for seminars at the international car electrics for dummies or where to put your probe?

Will spend tomorrow in the garage kicking the car.

many thanks Michael.

 

 

Hi Michael,

I have run such seminars at the Internationals in the past, and would be happy to do so again. (or via Zoom)

A CD of one of these seminars is available via the TR Register Main website under Resources. I do not gain financially from this, any fee goes to the TR Register.

TT

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Alan  thanks for the tips , have run extra earth wires from front valance earth points and lights now working , but I still don't trust them.

About a year ago at our local tr meet on the way back lights just packed in proper scary trying to drive with no lights?I would be happy for any advice so TT I will look into getting your cd on electrics and will look forward to your seminars when we get back to normal.

many thanks Michael.

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