Component parts and Assembly
Battery Compartment, Fuses & Relays

One of the first problems we encounter in an unfamiliar car is were is what! the battery & fuse box for instance? Not under the bonnet! Not in the boot surely cars haven't progressed that much, that they do not require a Battery? Unlike most cars the 'A' Class battery is right under the drivers feet, although if your cars got carpets you wouldn't know it? Remove the carpet and there you will see the tell tale black battery marked on a turn button, lift half the button and unscrew ant-clockwise to remove the floor pan and then the insulation pad covering the battery and there the fuse compartment and battery. I fail to see how anybody could not be impressed at this layout, this package is very neat and easily got at, far better than at the back of the engine bay where it was always hard to get at.

1 Battery. Ref. 2002 160 Petrol,=12volt 62 Ah, 280A Din.A80AEN or equivalent. Diesel vehicles normally call for a heavy duty battery, see hand book for details.
2. Positive Terminal.
3. Negative Terminal.
4. Battery clamp securing bolts.
5. Clamp Assembly.
6. Removable screw plugs for topping up Battery.
7. Heavy Duty Spade fuses.
8. Standard Spade Fuses.
9. Relays K7,K8,K9,K10. (See below for further details)
10. Relays & fuses information sheet. A 168 004 03 99
11. Fuse box/floor panel securing facility.
Note on the 2002/Feb Reg.160 Elegance, fuses 5,34,35,36,44, locations are According to the information sheet

The relays service the following:-K7. Fuel Pump.K8 Engine Management. K9 ESP/VGS or Automatic Clutch. K10 Rear window defroster.
For more information on fuse allocation Main distribution.

Note the position of the battery in relation to the fuse board the terminals are next to the board. With the battery terminals being of different size and the cable length being restrictive one could assume that it would be impossible to fit the battery incorrectly? Not so, at least one member of the BB Owners Club has managed to complete such a difficult task. Doing so can of course right off the whole of electrical loom and do other irreparable & terminal damage to component parts.
Its worth noting that in the case of this battery it can checked for acid level, unlike some batteries which are sealed.

It can be seen in this photo that the terminals are of a different size, the positive terminal is also marked and attached to it are several red wires indicating that they are live wires. Negative wires are normally black. For the battery to do its job connections must be sound & secure, and free from contamination. Many problems are caused where the earth component connections are either loose or have eroded away, All connections must be clean and secure if trouble free motoring is to experienced.
Cleaning terminals
If the battery terminals are dull dark lead colour then they can be cleaned using emery cloth which will remove the surface layer and expose shiny lead

DO NOT USE STEEL WOOL if the wool comes into contact with both
terminals, negative and positive it will ignite,(glow red and catch fire) also fine hair like
strands of the wool will be left in the area of the battery which can cause problems in the longer term. In this photo the battery is only a 9v fire alarm type battery, a large 12 volt will ignite the steel wool.

Knowing where to look for such connection of course is a different story ! Well I can confirm that there is a major earth terminal attached to the side of the sump of the engine, and on this model at least is not covered by any under body shrouding.

Note it is recommended that the battery be removed for charging. Before recharging or removing the battery make sure that you are aware of the warning signs displayed and take precautions to comply thus preventing accidents, whether it be acid burns, or explosion caused by fumes coming into contact with naked flames. It is always advisable to slacken the battery filler caps before re-charging your battery. I would not however fully remove them due to the acid bubbles which are formed as the charging takes place which will cause damage to anything it comes into contact with. The battery fitted to this model of Mercedes-Benz is fitted with a 'Gassing line' which allows the sulphur smell which are generated by the battery to escape to atmosphere. Only batteries with a gassing tube connection should be fitted where the battery is housed in the cabin ,albeit under the floor panel.

Battery Replacement
Some New Batteries supplied by MB and other outlets have the vent for the gassing line on the other end of the battery where this is the case if the battery has not got the change over facility, simply purchase a longer length of 7mm bore polythene tube & fit DO NOT TURN THE BATTERY ROUND or the battery will be incorrectly fitted with serious consequences for the car electronics. DO NOT allow the garage /supplier to talk you out of purchasing a vented battery just because they do not have one. It was standard equipment on the car when NEW and should be maintained to prevent a build up of fumes in the cabin.

I have just had to replace my battery at 4.5 years old. This a reasonable life for a battery, but as is the case with so much of today's produce technology has moved on.
I for instance have just purchased a Calcium battery, from Halfords Stores, a HCBO75 very competitively priced at 69.99 and with a four year guarantee, claimed to be maintenance free, have greater starting capabilities, with a 620amp cold cranking capacity, and a reserve of 110 minutes @25amps, which better than the Mercedes original fitted battery.
It also has the required vent, however this was at the other end of the battery which required the fitting of a longer 7mm dia breather tube costing only a few pence, which can be feed through the same hole in the battery storage area. In addition it also has the two positioning holes from the red positive terminal cover situated on the original battery, so if having you battery fitted make sure these items are taken car of and transferred .
if fitting the battery yourself you require a long socket bar and 13mm socket for releasing the battery clamp which is situated between the battery and the fuse layout. and also a 11mm open ended spanner for removing the terminals. and of course the original or replacement breather tube. Secure the terminal connection back away from the battery contact, this action also helps when fitting the new battery. Oh and have your car keys to hand because as you connect the negative terminal on your battery your car alarm will start to sound, turn it off in the normal way. Remember having removed the battery you will need to reset your windows, and ESP.

Before we depart this item please read this e-mail I received from a fellow owner it may help you?
The above battery was purchased and fitted on the 21.07.2006

I will now relate my experience 26.11.2009

As some of you may be aware I have been carrying an emergency battery pack for well over a year, however had to recently return it because the integral battery would not charge, so at present i have not got the use of such a unit. For details mypage.92
Halfords also now sell the unit displayed on that page, 49.00 ish very worthwhile carrying and saves waiting around for the AA who after 40 minutes had not shown up, in fairness they did say it could be an hour.

On the 23rd November 2009 I returned from an 11 day cruise having left the car in the port car parks at Southampton.

On return to the car it having stood out in the recent gales and heavy rain I unlocked the car and it started immediately and ran the fifty miles home like a dream.
I garaged the car and didn't need to use it until the 26th but on trying to start the car found the battery was almost flat and although the lighting was reasonable the residual power in the battery would not start the car.
I used my standard battery charger and after only about 15 minutes of charging was able to start the car I looked out the receipt for the battery fitted and confirmed the purchase date, the battery had a Halfords 4 year warrantee.
I completed the 15 minute journey and was confident having completed a small amount of shopping that the car would restart. No way, Nothing certainly not enough to turn the engine over although it it did try.

I contacted the AA and was told they would be about an hour.
I was in a car park but had I been on a main road with hundreds of vehicles racing past me I would not have been very happy or felt safe. The weather conditions and light were such that you would not want to wait outside the car and the battery condition was such that the vehicle lighting would not have lasted very long putting me and other road users at greater risk.
In this situation I would have sited my warning tri-angle and would have advised to police of my predicament and location.

While waiting for the AA I tried a couple of time to start the car, bearing in mind the engine was warm, I did eventually start, so cancelled the AA.
I then drove straight to Halfords store in Worthing where upon the battery was tested, the young man who needed some direction as to the location of the battery then proceeded to test the battery using a diagnostic battery tester, he informed me and I saw the read out/display which clearly confirmed the battery was in 'top condition', 'No Sir, your problem is not the battery' what about your alternator?' I insisted that was OK and although he offered to test it for me went silent when I told him where it was situated.

I asked him what the voltage was in the battery, stating that unless the battery was fully charged it would not start the car, he indicated 45% charged, bearing in mind that I trickle charged the battery to fully charged just before leaving for the cruise I knew there had to be a problem with the battery. I didn't get an answer on the voltage question.

He then confidently asked me to start the car, it wont start was my reply, this was confirmed when I tried, however when he reconnected his diagnostics tool the dispay showed thet one of the cells had a short circuit.

So if you suffer a similar problem, Yes Halfords is the place to get your battery tested but make sure the test is done after just having tried to start the car. The old battery was given a clean bill of health until it was testing after having just tried to start the car, had the original reading been taken as correct I would still have a problem which could have cost hundreds just getting the car to a garage and then them trying to locate a fault which didn't exist.

My diagnoses was confirmed as correct and a lot time and aggravation was saved.

Halfords replaced the battery with a new unit without question once the diagnostics confirmed the problem, this battery only has the balance of the 4 year warrantee i.e. 5 months but I'm confident it will last a lot longer than that, so it was a close run thing and nearly cost me a new battery.
The new battery on the right, the one fitted is a 'maintenance free' unit which as far as i can see makes it impossible to check the fluid levels, however this is modern technology and so I hope it performs well.
Note. The A & B in the photograph this shows the breather tube fitted and also the blanking plug fitted into the alternative breather tube fitting. Make sure that the company fitting the battery do fit the plug which is attached to the positive terminal protection cap when in storage.
Halfords staff having fitted the new battery and as i expected the car instantly started.

However where I had tried to start the car while waiting for the 'AA' (Automobile Association) I had caused a condition where the Engine management light had come on and now remains on when the engine is running.

To me this is not a problem as I have my own hand held diagnostics tool with which I will delete the light, however it could cost as much for Mercedes-Benz to delete that light as it would for a new battery, so the tool purchased is a good investment.
I intend undertaking that small job as well as re-setting the electric windows first thing tomorrow. I re-set the ESP/ABS before driving home. I will let you know how I get on.
Follow up 27.11.2009 Windows re-set and Engine management light deleted 10 minutes maximum. for details of the Engine management light deletion, see page 69.

Do be prepared to assist Halfords store staff by knowing where your battery is located, they are changing batteries on all makes of cars and from my own experience it is difficult to remember them all if indeed you have come into contact with the specific make and model of car at all. If your wife drives the car, give her the information as well, it all helps reduce the aggravation when such incidents do happen.

For diagnostic tools see page mypage 69 please not that the model I have has been superseded by newer models. link to see options
I have just procured a Halfords battery HCB075 for my A160 and on placing the battery into the box it would not go into the lower recess at the bottom rear of the battery compartment as a result the retaining bracket will not slot into the box. Halfords batteries have a shaped plastic strip added to the retaining bars on the bottom of the battery. Remove them by pulling up as they are pegged into the battery bar. Fits easily then! These strips are not easily noticed, you need to compare batteries before installing. Thanks for you fine articles found after recharging old battery in place without disconnecting, now have EMS light on and despite removing and installing cables in correct order still on, so over to Mercedes in Cheltenham for 90 and hour check??!!

Remember if you want to avoid the problems with the ECU management light, turn your lights switch to at least side lights, to reduce the power serge going to the ECU when the battery is connected. There's more information on battery care in an article I prepared for go to :- Click Back to return

Relays location

There are more relays housed in this box if all are present then according to the sheet there should be six!

Having removed the three star drive screws which are retained in the lid when fully unscrewed, release the three clips situated one either side and one at the bottom right hand corner, If you ease the lid away at the top and then down you will not need to worry about undoing the bottom clip, re-install in the reverse order. Inset photographs above show the star drive screws 1 and the 2 tool for unscrewing them as the clips. when you first open the box you will be confronted by just a mass of wires coming from the various looms going to the ECU plugs etc.

The middle portion of the box where I thought I would find the relays was filled with a removable foam, when removed it revealed just and empty compartment. But I knew they were there because Mrlapou had said pull back the carpet, passenger side and you will see relays there, yes they were, but you couldn't get at them they had to be got at from the engine bay. Determined to locate them purely from an interest/owner point of view, I then removed with extreme caution because of all the wiring, the foam packing from around the loom/cable, clearly shown in the photograph, there they were recessed at least four inches where only E.T.'s fingers could reach! Obviously never to be got at once fitted? That wasn't a problem because I had no intention of getting at them. I just wanted to be aware of the location. In fact I'm now starting to feel sorry for the Mercedes-Benz technicians who might one day have to replace one or more of them.
1 Major loom connections
2. Foam packing, relays lay behind.

When the foam packing is carefully removed the relays can be seen care should be exercised not to unduly disturb the masses of wires that come together in this area. Of course the next question is there are only four while the information sheet indicates there are six, so what do they service? Well Nick the Technician of Mercedes-Benz Chichester West Sussex came to the rescue again. Apparently different models will have more of less relays, depending on the services they require Auto gear box for instance will require the Starter lock out relay. In the case of the 160/2002 Elegance, with manual gearbox only four of the six listed relays are required.

K1.Washer Pump. K2 Horn. K4. Engine Cooling fan. K5. ESP pump. While looking at the relays it is worth noting the white clips on either side of the relays that engage on small studs locking them in place, this applies to all the relays including those in the main fuse area under the drivers feet.

Fuse box for lighting, on RHD models it is located on the O/S, end of the dash, between the door and the dash. This fuse facility provides protection for lighting. The two fuses at the top of the layout are spares, Information on what these fuses protect is displayed below and is also available on the inside of the grey fuse box cover , albeit would be very difficult to read after dark.
There are two spare fuses in the lighting fuse box 1x 15amp (Blue) and 1 x 7.5amp (Brown) bearing in mind that these fuses power lighting only, it must be worth familiarising yourself with them in daylight? Logic says you will only find you've got a problem after dark!

The information displayed in the grey panel below is moulded into the inside of the fuse box cover, Fuse numbers and size in the photo have been highlighted for ease of reading the information on the left has been extracted from the relays & fuses information sheet located in the main fuse box.

Fuse layout shown is relevant to the 'A' Class 2002/160 Other models may vary in layout and or rating of fuses. This document added to your hand book would make a very useful supplement, enabling you to check the slot number of the fuse & the rating. When it comes to actually replacing the fuse you will be able to confirm that you have placed the correct fuse by colour into it is correct location. Where there are empty slots in the same area, its very easy without a reference to place the new fuse in the wrong slot, and if you do, it can take an age to sort out. Why do not the fuse manufacturers make blanks say in black, nothing on them must mean 'blank' perhaps I'm being a little too logical? Save a lot of agro, I filled the gaps in with a blank fuse, On this model at least you will now know where each fuse is situated.

The most useful of tools on a dark cold wet night has got to be the fuse puller, the average male fingers are too large to pull the fuses without some assistance, and even if you do achieve it your fingers will then cover the very part of the fuse that you want to examine. The puller not only allows you to pull the fuse but holds it in such a way that you can inspect the fusible link 1 (the part of the fuse designed to melt, burn out, thereby protecting a wiring circuit or electrical component) you can also replace the fuse with the holder. With the puller shown the older type barrel fuses can also be pulled. with the acceptation of the barrel fuse, the fuses shown are those found to be in use on the 'A' Class A160/2002 there are other values, Mauve for instance although not found on my car. do not forget you also have two H.D.Fuses 60 & 80 amp. The colour of fuses generally is standard but may vary slightly, more so in the cheaper brands.

Two sizes of spade fuses are fitted to the 'A' Class, heavy duty and standard, although the standard can be obtained at most accessory shops the heavy duty spares are not so readily available. Halfords for instance do not stock them, so make sure you still have the two Heavy Duty, Spares 80, & 60 amp, they are housed in a slot on the main fuse box. Murphy's law says if you have got a spare you will never need it!

A couple of coloured pages in the MB 'A' Class handbook wouldn't go amiss, so why not add your own as I have done, a most useful addition

Following a recent incident where a member of the BB owners club had difficulty in locating the fault on a headlight bulb, I thought I would just mention the merits of owing a meter for measuring ohms, amps, volts etc, anybody who feels confident enough to deal with minor problems on electrical circuits, bulbs, fuses, relays, coils, wiring, etc really can't afford to be without a meter, they are very affordable and are reasonably straight forward to use.Fig.1. shows that the fuse is sound, Fig.2. is indicating that there is resistance and therefore the fuse is defective, by either dirty spade connectors or a broken link. The checking of electrical components, fuses, and some bulbs for that matter, particularly where they are orange or fogged glass are very difficult to check without a meter. Our fellow member did finally find, I'm sure to his relief a hairline break in the responsible circuit fuse. It is highly likely that the meter would have picked up the problem earlier being far more accurate than a visual inspection. Voltage, Amps and resistance in circuits can also be checked.
As with the meter shown in the photo meters can be Multi purpose and are able to read AC/DC voltage etc,
But unless you are fully competent,
Do not be tempted to use them on AC Mains Electrical Circuits 240/250 volt, you are best advised to leave all defects, repairs, etc to a fully Qualified Electrician>

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