puzzling front sidelight 300TDI

was about to put my 90 300tdi through the MOT last week, noticed that the front nearside sidelight was out - went to replace the bulb and still nothing, checked fuse 15 - seemed ok but replaced anyway.

checked continuity from the lamp holder to earth - yep that's fine - checked the voltage and its reading 2.8 volts back to a good earth.

when turning on the lights, first click is sidelights - drivers side is ok (dim headlights) rear lights are on, second click is headlights - thats all ok including main beam.

I still cant work out why the nearside has just 2.8 volts - has anyone got an idea - really need my landy through the MOT now..

thanks all

A multimeter is very sensitive when checking continuity. That doesn't necessarily mean that it will have a low enough resistance for the 12v supply to use. This seems like a dodgy earth to me.

Al2O3 said:

A multimeter is very sensitive when checking continuity. That doesn't necessarily mean that it will have a low enough resistance for the 12v supply to use. This seems like a dodgy earth to me.

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i'll run another earth and see how it goes - thanks mate

Have you tried a spare connector?

I had a crack in one a few years ago that took me ages to find.

youll probably find a new lamp and connector will help

no - that didnt work - noticed now that there is no voltage to the light and around 7ohms resistance to the earth on the engine..?

i changed both lamp and connector for a new set i had - still no luck

robbiemcvee said:

no - that didnt work - noticed now that there is no voltage to the light and around 7ohms resistance to the earth on the engine..?

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So the 2.8v has dropped to zero?
How are you measuring the resistance, via the earth, to the engine?

yes - the voltage seems to have gone - not sure why...im measuring the resistance form the light connector earth (black) to the engine

robbiemcvee said:

yes - the voltage seems to have gone - not sure why...im measuring the resistance form the light connector earth (black) to the engine

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So, with your multimeter you can get an obvious and good connection to the red/black supply wire and a good earth and get 0v when the switch is on? Is the tail light still coming on as they share the same supply from the fuse?

Hello, yes the rear lights both work

robbiemcvee said:

Hello, yes the rear lights both work

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Then the only two options, to my mind, are a break in the red/black supply wire (unlikely) or a bad earth from the front lamp connector. If the earth isn't good the electricity will simply go via the rear bulb to earth as they are in the same circuit.
Try taking the rear bulb out (on the same side) and see what happens.

Thanks again, ill have a go tomorrow, run out of steam now

robbiemcvee said:

Thanks again, ill have a go tomorrow, run out of steam now

Click to expand...

Aye, it's beer O'clock

Looks like a break in the cable to the positive, is these a connector hidden somewhere that takes red from the fuse to the red/black on the connector

robbiemcvee said:

Looks like a break in the cable to the positive, is these a connector hidden somewhere that takes red from the fuse to the red/black on the connector

Click to expand...

No, don't think so. Are you testing that live via a different earth, not the original earth?

All fixed, cut the wire next to the bulkhead and spliced a new one in.. mot next week..!