cliffcoggin

Renato. If "wd, d" means WD40 you would be better served by an ordinary mineral oil. WD40 is evil muck that dries to a sticky gummy coating that could make the problem worse. For those who do not know, WD40 is the 40th water displacement formulation that was tested in the search for a coating that would protect steel against rust. It serves that purpose very well but it is not, and was never intended to be, a lubricant.

If you need to buy a new battery get it coded to the car else you will have more problems than you have now.

I see no picture.

Russell. The prime candidate is a weak or defective battery. I suggest you get the battery professionally tested before looking for other causes of the fault.

There is no magic solution to this unless you are prepared to spend hundreds or even thousands of pounds on engine modifications. For the average motorist who does not want to modify his car the recommendations are same as they have been since the dawn of motor cars a century ago: 1/ Service it regularly. 2/ Maintain the correct tyre pressures. 3/ Be as gentle on the accelerator and brake pedals as possible.

I would fit a new chain while I had access, to avoid doing the job a second time at a later date. Chains stretch over time until eventually they are longer than the tensioners can accomodate.

Probably the compressor as mentioned in: https://www.audiownersclub.com/forums/topic/27161-rear-suspension/#comment-106137 https://www.audiownersclub.com/forums/topic/26506-front-suspension-strut/#comment-102910

I wonder if the previous owner of the car was, shall we say, rather large, and has damaged the seat. Try the passenger seat for comparison.

Are you running them at the correct pressures for that particular size of tyre? Look in the handbook rather than relying on a tyre vendor's recommendation. What pressure guage are you using? Those on garage forecourts are notorious for errors, as are the cheapies from the likes of Halfords. The cost of a decent guage will be repaid many times over in longer tyre life. Are you testing the pressures cold or hot? Cold is normal.

Overhead switches, if such things still exist?

Worn alternator belts make that sort of sound.

Dogbone link. I like that name Stevey, and must try to remember it. It describes the part exactly.

Ir would be worth getting the battery professionally tested because defective batteries can play havoc with the car's sensitive electronics. I stress a professional test because a simple multi meter reading of 12.5 volts will not reveal any internal faults. Let us know the outcome of the test before we explore other causes for limp mode.

How old is the battery?

Does your car have anti-rock strut connecting the top of the engine to the bulkhead? If it does, check the rubber bush.

So did you get the sidelights to work? I've never heard of rain lighting. Can you explain further?

The most likely culprits are the CV (constant velocity) joints. Does the knock become worse when the steering is at full lock?

Neil. I imagine that has all the necessary connections. The next step is to inspect and test the wiring harness to the door.

Simon. If you frequently have a heavy load in the boot it would be worth investigating whether upgraded springs are available, and of course change both for a matched pair as Gareth mentioned.

If that means you are unsure which fuse to use you should choose carefully. You need to find one that is not permanently live (i.e. only comes on with the ignition,) else you will flatten the battery overnight. Your plan of using a piggy back fuse is a good one as it maintains the principle of one device per fuse. Check that you can close the fusebox cover once the extra fuse is fitted. Doing precisely this job on my A3 some years ago was what led me to this forum.

If the 7.5 amp fuse supplies some other circuit in addition to the satnav I suggest you leave it, or even uprate it depending on the total electrical load it carries.

Does courtesy not exist any more?

Did the new lock have an integral switch, or did you attach the old switch. The other thing to look at is the wiring between door and pillar. The wires had a habit of breaking in the older A3s.

Kelly. For information there are two stages to starting an engine: 1/ cranking, (or turning over,) when the starter spins the engine to suck air and fuel into it; 2/ ignition, (or firing,) when the fuel/air mixture in the engine ignites. Yours is clearly not turning over so likely it is an electrical fault somewhere between the switch and the starter relay. I doubt that the starter motor itself is faulty because the instrument lights stay bright. Your plan to recover it a garage is a good one.

An internet search found this place at Barnard Castle, which is a county away from you. Perhaps you can find others a bit closer. https://www.carrosserie.co.uk/