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It sounds like you may have a worn rear strut or rear strut mount bushing. According to the RepairPal estimate page, (http://repairpal.com/estimator) 1 rear strut replacement runs from $218-$318 and the mount will only add another $25 or so dollars. It is recommended to do both sides at once.
Do you have a 2-3 speed wiper or a variable speed wiper? If it is a 2-3 speed wiper, it could be your wiper switch or your park switch inside the wiper motor. If it is a variable design, then it could be the module or the wiper switch. Can you change the speeds of the wipers? This indicates there is still some functionality in the switch.
It sounds like there is a short in the seat heater grid, that is why there is one spot getting so hot. I would not run the seat heater until you fix it. It could catch on fire or short out your electrical system. If the seat grid is not available as a separate unit, you could possibly a used one from a good quality wrecking yard and then have a shop that does seat work install it. I use to rebuild seats in dealerships and later in my own shop, so some places still do it.
I worked on an early 1990s SAAB that had this type problem and it turned out to be an intermittent failure of the fuel pump. I made the conclusive diagnosis with a fuel pressure gauge taped to the windshield and when the car acted up, the fuel pressure dropped like a rock. Generally, if the problem is Ignition related such as an Ignition module, it just shuts off cleanly and suddenly and won't restart for 1/2 an hour or so if at all. Fuel tends to be more of a loss of power, sputtering etc. If it is a fuel pump problem, then always replace the pump, pick-up sock in the tank, the fuel filter and fuel pump relay as one job. Many places will try to cut corners and the car will still have some weird problems down the road. ( A dirty pickup sock can be a total pain to diagnose )
There was a bulletin on 2.3 liter Quad Engines for the Coil packs and Coil Housings. ( they would arc and fail) Are you using AC Delco parts? Are you replacing the plugs, coil boots, coils and coil housings all at once, because when I did them at the GM dealship, that is what we had to do, or the car would 'come back'? Do you have any ignition module codes like code 42 for lack of EST timing. If the module is over heating the coils because of too much 'on' time then this could be a factor.
The Ignition Coil(s) are inside the valve cover. There are 3 Ignition coils, 1 for every 2 cylinders. You have to remove the Air Intake tube and then remove the plastic cover over the Coils and Ignition wires. Are you sure that you mean the Ignition Coil(s) because for a 1995 3.2 liter Mercedes 6 cylinder ( straight six ) that is where they are? I just did some last week and have done lots of Ignition work on these Engines. ( The Coils wear out at about 100,000 miles ).
Typically the time to diagnose a defective Oxygen sensor is about 1 hour. This involves test driving the vehicle at least a little bit, reading the code, writing down the freeze frame information, visually inspecting the sensor and its connections and lab scoping the output in terms of voltage bandwidth and rise time from its leanest readings to its richest readings. Some people will cut corners and just pull a code and then recommend a sensor, but this isn't very professional. In California when you do a Diagnosis for an Emissions Test Failure, even if there are no codes for the sensor, the steps I just described are the bare minimum. The Front Oxygen sensor takes about .3 hours and the rear about .5 hours. Be SURE and let the car COOL down or you will really, seriouly burn your self. Then clear the code and do a monitor setting test drive which is basically driving at 55-58 mph for about 4-5 miles with out interruption. This sets the Oxygen sensor monitors very fast.
This generally means that you have a problem with the horn contacts inside your steering wheel and steering column. Possibly a piece from the horn contacts have broken off and fallen inside your steering column and it is grounding and activating the horn and the wiper lever moves it away from metal and therefore stops the horn. This is not uncommon.
The 'safe mode' of your radio means that you need to wait before entering the proper code. As far as your car not starting, did you have the key in the ignition when changing the battery? I ask this because you may have possibly blown a fuse with the key in the ignition. Be sure to check all of your fuses absolutely thoroughly. Does the car turn over quickly or does it turn over slowly? Most European cars will not start if the the battery is not absolutely fully charged and I have seen this from a brand new battery that was on the shelf too long.
Do you ever get a Check Engine Light On? This could indicate that there is a fault code for your tranmission problem or from an engine sensor or transmission component that is having a problem.