How do you install a Radio in a 1979 Mercedes 300D? Do i need to run a wire from the battery to the yellow wire on the aftermarket harness? Do i tie the orange (illumination) wire to the red wire? Also on bypassing the fader answers. Thanks
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W123 chassis requires additional wiring for backup (memory) power and illumination. The latter can be dimmer controlled or fixed. Power for backup can be connected to hazard warning flasher switch, terminal 30, red with white stripe. Be sure the aftermarket stereo has a dedicated fuse for backup power, typical fuse sizes are 1/2 and 1 amp. Harness to the hazard warning switch is beneath console cover. Power for dimmer controlled illumination, terminal 58d, gray with blue stripe, is available at rear of Climate Control push-button panel. There is a cluster of lamps lighting the CC panel. For non-dimmer controlled illumination, power is available at terminal K, gray with violet stripe, feeding the gear shift lamp. The gear shift lamp harness is to the left of shift selector housing. Front-rear fader is rated for low power (less than five watts) so it is advisable to unplug loudspeaker connector from fader and connect aftermarket stereo directly to the four loudspeakers. Using stock fader with aftermarket stereo can cause the control to burn out due to excessive power dissipation. Unused stock fader can be left in place or removed and replaced with a blank cover. FYI: connecting yellow wire to red as mentioned prior will cause the radio to lose memory presets, since backup power will be removed when ignition key is switched to off.
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If I read your question right, you have an after market radio to install. The radio should have wiring diagrams to help out. Generally, Red is positive and Black is negative for 12 volt power, use a meter to verify polarity. The Yellow wire is connected to positive (you can connect it with the Red wire). Fading is used to change the balance between front and rear speakers, if you only have one set then use the wires from the harness to connect them. For good sound quality, make sure that left negative goes to the negative wire of the speaker, left positive goes to the positive wire of the speaker. The Orange wire should connect with the dash board lights so that the radio illuminates when the dashboard is illuminated, it can be connected with the Red wire if you want the radio to illuminate all the time.
You can make the wiring easy if you buy some automotive splice connectors (usually blue plastic, allows one wire to pass through and the other wire end gets connected by a metal blade that cuts through the insulation and grips the wire itself.
The hardest part of replacing a radio with a non OEM radio is getting the unit to fit snugly in place.
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