Radio - CD Capable System Upgrade
REF. NO. MBNA 82/51TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: August 1991
SUBJECT:
M.Y. 1991 MODELS 124 (EXCEPT 124.090/290), 126 AND 129 REPLACEMENT OF SINGLE UNIT RADIO WITH TWO-PIECE CD-CAPABLE RADIO
Serial Number Range
For a few early production model year 1991 vehicles, it is possible to replace the factory installed single unit radio with a two-piece CD-capable radio. A two-piece radio can be identified by the presence of the "Mode" button (marked MOD) on the radio. The list of vehicles involved which are prewired is shown:
The two-piece radio consists of a head unit containing the operating controls and cassette player. This unit must be installed in the center console in place of the current single unit radio. A second unit, the tuner/amplifier must be installed in the trunk. The vehicles are equipped with the main power, data-bus and speaker cables. However, additional wiring and hardware is required for the installation of the two-piece radio.
Procedure:
A. Installation of Head Unit
1. Remove radio from center console (job no.82-505). If vehicle is equipped with sound system, remove preamplifier from radio.
2. Locate the two-piece radio wiring harness and identify the cables for power, ground, speakers, and data-bus.
3. Connect the speaker mating connectors.
Important!
On vehicles equipped with anti-theft alarm system, locate the 5-pole anti-theft/speed signal plug. Open the plug cover and remove (cut off) the bridge from pin 4 to pin 1 (0.75 br wire). Reassemble plug and connect to radio. On vehicles not equipped with a telephone, the radio will stay in the telephone mode (display shows "TEL") and not play, if the bridge from pin 4 to pin 1 is not removed.
4. Connect the power mating connectors.
5. Connect the cables for power, ground, power antenna and data-bus to the respective connections on the head unit.
6. Install the head unit.
B. Installation of Tuner/Amplifier Unit
1. Depending on the model, the units are to be located as follows:
124 (except 124.090/290) and 126 trunk area, right side, behind liner
129 (except vehicles without trunk area, left
tuner/amplifier mounting studs, see 5.3) side, behind liner
2. For installation of the tuner/amplifier unit, remove the left and right side liners (model 129 left side only).
3. Remove the panel in front of the fuel tank (except model 129).
4. Locate the automatic antenna, disconnect the signal cable and connect the supplied short antenna signal cable.
5. On models 124 and 126, route the antenna signal cable along underside of shelf below rear window to the location of the tuner/amplifier unit. Secure cable alongside existing wiring harness using cable ties and clips.
6.1. Model 124, equipped with:
- active bass system (Figure 1), remove bracket and active bass amplifier/control unit (N40/3) from behind trunk hinge bracket. Mount tuner/amplifier unit on new bracket 124 820 70 14. Place the assembly behind trunk hinge. Place intermediate bracket 124 820 68 14 in front of trunk hinge bracket and fasten all to hinge bracket using the supplied nuts.
- sound system (Figure 2), install the basket for the tuner/amplifier using the sound system amplifier bracket mounting bolts.
6.2 Model 126 (Figure 3):
Place the tuner/amplifier unit in the basket and install both at the right rear wheel well by mounting the upper and lower brackets with the supplied sheet metal screws.
Note:
In vehicles not provided with a predrilled mounting hole for the upper bracket, temporarily locate the tuner/amplifier unit and basket 1 9/16 in. (40 mm) from the bend (A), mark and drill a 5/64 in. (2 mm) hole (1). If holes are not provided for the lower bracket, also mark and drill two 5/64 in. (2 mm) holes (2). Install tuner/amplifier and basket with the two brackets using the supplied sheet metal screws. (Figure 3).
6.3 Model 129 (Figure 4):
Place the tuner/amplifier unit in the basket and temporarily fasten the assembly to the studs in the fender above the bumper. Install the upper mounting bracket for the tuner/amplifier basket with the supplied screw. In vehicles not provided with a predrilled mounting hole for the upper bracket, first mark and drill a 5/64 in. (2 mm) hole (1, Figure 4).
7. Reinstall the preamplifier if previously removed (see step 1), by fastening it on the tuner/amplifier unit.
8. Fasten the tuner/amplifier unit to the basket by lining up the securing holes of the unit and the bracket, and securing it with the supplied bolts.
9. Locate, identify and connect the cables for power, data-bus, antenna signal and speakers on the tuner/amplifier unit.
10. Properly secure all cables with cable ties and reinstall the removed panels and liners.
11. Consult the Radio Operation Guide of the new radio and test the operation of radio and cassette player.
Parts Information
Recommended Time Allowance: 0.5 hrs.