Vehicle - Caution Regarding Aftermarket Electrical Acc.: Overview
REF.NO. MBNA 54/35TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: November 1991 (supercedes MBNA 54/12, October 1986)
Revision:
This Service Information contains information relevant to new models.
SUBJECT:
ALL MODELS
INSTALLATION OF AFTERMARKET ELECTRICAL ACCESSORIES
To help prevent damage to existing components or wiring harnesses during the installation of aftermarket electrical accessories (such as cellular telephones, radio transmitters of any type, or custom audio systems) the following recommendations should be considered.
It is strongly recommended that any outside firms doing electrical accessory installation work on any Mercedes-Benz vehicle be advised of these important guidelines.
1. Never splice into existing vehicle wiring harnesses in order to gain access to power, illumination or ground circuits. This is especially important for safety related systems such as SRS, ABS, etc.
Devices with current requirements of 5 amperes or more should be connected either to the main power distribution terminal block X4/10 (circuit 30) in the engine compartment or directly to the battery. A proper size in-line fuse must be installed as near as possible to the connection point.
Devices with current requirements of less than 5 amperes should be connected to the connector block for accessory equipment (X30).
In model 126 vehicles without heated seats, the connector block (X30) must be installed prior to accessory installation by referring to the Work Instructions no. 265.
2. Always check behind trim panels for the presence of wiring, hydraulic or electronic devices before drilling holes for the mounting of accessories. This is especially important near the right and left sides of the center console, the driver's and passenger's foot panel and kick panels, and the rear storage compartment area of model 129.
3. The fuel tank is located between the rear seat (partition panel in model 129) and the trunk. Never drill or install fasteners in this area without first removing body panels for visual inspection. Never mount components to the partition panel by using sheet metal screws, which may protrude though the panel and contact the fuel tank during normal driving or in the event of a collision. Scratching the fuel tank paint may result in corrosion and eventually a fuel leak.
4. When wires are routed through metal panels, always use the existing body wiring grommets and seal any openings cut into the grommet.
5. Never wrap wires around fuse holder spring contacts to obtain power for accessories which require "switched power (circuit 15). Power from the output of the ignition switch can be obtained from the cigar lighter (less than 2 amperes), the connector block for accessory equipment X30 (less than 5 amperes), or the terminals on the underside of the fuse box.
6. When installing a radio transmitter of any type (including cellular telephone, citizen's band or amateur radio equipment), be sure to use only high quality coaxial antenna cable and connectors Keep the antenna cable as short as possible, and route it away from existing wiring and components. The antenna system must be properly grounded and adjusted for minimum VSWR. Avoid locating the antenna near existing electronic components. The preferred antenna location for high power (> 20 watts) transmitters is the center of the trunk lid, or the center of the roof for magnetic-mount types.
7. Always solder all connections. Splices and terminals cannot be properly crimped in the field without special tools.
Power should be obtained as described below. Always use a proper size fuse for any installation.
Ground should be obtained at the nearest chassis ground point. Consult the Electrical Troubleshooting Manual for ground locations.
Component locations