Messerschmitt Electrical Systems

We are very fortunate that the KR200 electrical systems are built to the highest standards and are a credit to the original designer. In this case it was probably not Fend although the design and protection systems suggest the work of an aircraft engineer. Even the KR175 is wired to the best available technology of the day and this must have added some additional costs. Fortunately, when FMR took over from RSM in 1958, there was no attempt to reduce costs by skimping on the electrical system and the wiring remained the same right up to the last vehicle produced during 1964. Many of the original wiring assemblies are still in excellent condition and restorers usually only need to replace the wiring if the car has been stored in a corrosive atmosphere for years.

Each circuit is individually fused with separate fuses for each headlamp filament and two independent side light circuits. Thus, when a fault does occur, it is much easier to trace because a minimum of components is affected. Furthermore, if a fault occurs out on the road, there are still enough lighting circuits operational to allow you to continue your journey. The fuse box has eight separate circuits, the top two are for ignition switch controlled circuits such as the windscreen wiper and flashers. The remaining six are for main and dip beam headlamps, and left and right side lamps. All should be rated at eight amperes maximum, check yours now! Correctly sized new ones are available from Partsmart. All wiring assemblies are fully sheathed in PVC giving much greater mechanical protection than the taped wiring found in may modern cars. Each circuit is numerically coded according to German vehicle electrical standards and the same system is still in use in today?s German cars. Even the cable colours are similar and easily identified by those familiar with the standard. There is one major weakness in the design in that there is no protection for the main power and ignition coil circuits. If a short circuit occurs in the main red power cable (code number 30), the black ignition coil circuit (code number 15), or the feeds to the headlight dip switch, then the cable system will be severely damaged. When this happens the car will fill with grey smoke and may catch fire, only a quick disconnection of the battery will save it. Until recently, the batteries suitable for the Messerschmitt battery tray did not have sufficient power to create major damage and the internal resistance was often high enough to give time to disconnect the battery. January Kabinews detailed two separate incidents of short circuits, one of which caused injury to the owner from trying to disconnect the affected cables. Recent developments in battery design and the introduction of high-powered motorcycles with electric starters have led to the introduction of small high power batteries. Thus it is possible to fit a battery of 36 Ampere Hours into the same battery tray that would previously accommodate a battery of only 14 ampere hours.

Always fit the most powerful battery available to fit the battery tray. Gell cell batteries are particularly useful on a Messerschmitt. Starting current does not normally exceed eighty amperes and this is well within the battery capabilities. Originally intended as back up power supplies for emergency lights and alarm systems, they are completely sealed and can even operate inverted. These batteries must be re-charged at a low rate as there is only a limited provision to vent off the hydrogen gas produced during high charge and discharge rates. All have charging instructions and warnings on the case about over-charging. In normal use, the SIBA or Bosch dynastart does not provide enough power to overcharge the battery and output is regulated anyway by the current / voltage regulator. Dynastart output is barely adequate at the best of times and a quick calculation of the wattage of the various bulbs reveals that there is insufficient reserve power available from the maximum 135 watt charging output of the dynastart. Sachs and FMR put out dealer notices when the cars were in production warning that the battery required weekly re-charging if the car was used for short journeys in winter when the lights were in use. Many people believe that a larger battery will overload the dynastart charging circuit. In fact the reverse is true, a larger battery will be less loaded during the starting phase and will require less power to recharge. However, the high current available from these batteries will allow the Dynastart to be used for a long period before the battery is flat. Avoid using the starter continuously for more than twenty seconds and be sure to allow intervals of five minutes before operating the starter again. This will allow everything to cool down thus preserving the life of the Dynastart.

While there are many benefits of using a high capacity battery, one danger is the previously mentioned unprotected circuits and the additional capacity can allow sufficient current to pass to cause a fire. One way to avoid this is to place a fuse in the main red power cable at the rear bulkhead terminal strip. Partsmart now offers an in line fuse of 30 amps rating to protect this circuit. Simply disconnect the large red wire from the terminal strip located at the rear bulkhead, insert one wire of the fuse-holder into the vacant terminal and re-connect the red wire into the terminal provided with the fuse holder. One spare 30amp fuse is provided with the holder and the standard replacements can be obtained throughout the world.