Sidelight problem.

[Rizzo]

I have a problem with the left hand sidelights, When I turn the switch to "on" I get right hand sidelights only. Both bulbs on the left are fine, as is the fuse. All other lighting is working fine. With the ignition off, I put the indicator stalk down to activate the left side parking lights....and they come on!. So, where is my problem? Any help greatly appreciated. Thank you.

[Magnet]

Hello Bob,

Although I would not like to say that this is the answer to your problem, I would be first looking at the wiring harness as it passes from the body to the boot/hatchback area i.e. the flexible rubber-covered section. 

It would be worth carefully pulling back the covering and inspecting the harness cables for breaks. It is not uncommon to find a broken cable/s within this section, and this is caused by the harness flexing at this point over a number of years of use. A cable usually breaks/starts to break  ( if its going to) during colder weather where the cabling becomes less flexible.

Have a look and let us know how you get on. 

Kind regards,

Gareth.   

[Rizzo]

Hi Gareth,

I spent most of the day yesterday checking every cable and wire I could get to, still no luck.

Thank you for the advice anyway, I don't suppose you would have any more ideas?

Best regards,

Bob.

[Magnet]

Hello Bob,

Many thanks for coming back on this, and I’m sorry you haven’t been able to find an explanation. 

A couple of points :- are the brake lights and indicators on the LHS working correctly? Although I don’t think this is the answer, have you made sure associated earthing points are sound? Last option, do you have, or can you get, a wiring diagram for the car - I assume Haynes may have covered this model back then? 

Although you have checked the main fuse, circuits at this time were sometimes safeguarded by additional in-line fuses, and you would need to check if this applied to your car and if so, you need to locate and check it. Confusing bit however would be that they work via. the parking light circuit, but....

Can we take it your cable checking did include stripping back the flexible rubber harness section? 

I’m afraid Rob that much more than the above will probably point you to the worth of buying an hour’s time with a trusted local auto electrician.

Kind regards,

Gareth. 

[Rizzo]

Good morning Gareth,

Well after exhausting my limited electrical knowledge, I've had to do a bodge up job.

I've just ran a wire from the right side tail light to the left one, works now, but for how long I don't know.

Regards,

Bob.

[Magnet]

Hello Bob,

Well, fair do s, as we say around here - that’s one way of getting around it. If this were mine, I would be putting an in-line fuse in the added bypass cable. A bit of a must in my book. Fuse value? Depends on the cable you have used, so could be 5 amp, but irrespective of the cable, I would say do not use a fuse greater than 10amp. 

Kind regards,

Gareth. 

[The Brummie Mechanic]

Hi firstly what model do you have and age? If it's an early a3 for example it could be your convenience unit aka body control module.

If the fuses are good replace it anyway. I have had hairline cracks in fuses before causing lots of swearing lol.

If you have a decent tester, check for a nice solid battery voltage to each sidelight, if you have an odd voltage like 9v then the cable is shorting to another power source somewhere. Also check the power to a good ground point, make sure you have 12.5v ish. 

Check continuity to ground from the plug to the respective ground at both lamp units, A good resistance should be about 0.1 ish ohms. If it's open circuit there's your problem.

 

Happy to help if you need more help on anything

 

Chris