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The body control system consists of the following 3 modules:
• The Dash Integration Module (DIM)
• The Instrument Panel Module (IPM)
• The Rear Integration Module (RIM)
Each of the 3 body control modules integrate a number of functional systems under the control of a single module. Each module is connected to the Class 2 serial data circuit, many of the control functions are implemented by Class 2 messages.
What system (S) are you having problems with ?
Rear Integration Module (RIM)
The various RIM inputs and outputs are described in the corresponding functional areas as indicated on the RIM electrical schematics.
The RIM functions include the following:
• Automatic level control
• CIGAR relay control
• Class 2 communication requiring RIM interaction
• Content theft deterrent
• Fuel door control
• Fuel level sensor input
• Heated seat control
• HVAC blower control
• LK/CYL relay control
• Park brake relay control
• Rear defog relay control
• Rear park assist chime control
• Retained accessory power (RAP) relay control
• Reverse relay control
• Transmission shift inhibit
• Trunk release relay control
• Various controls for the interior lamps
Instrument Panel Integration Module (IPM)
The various IPM input and output circuits are described in the corresponding areas as indicated on the IPM electrical schematics.
The IPM functions include the following:
• 54 volt VF display input
• Ambient light sensor input
• Class 2 communication requiring IPM interaction
• Fog lamp switch inputs
• Front HVAC air delivery controls
• Front HVAC sensor inputs
• Front HVAC temperature controls
• Fuel door and rear compartment lid release switch input
• Hazard switch input
• HUD active control
• Instrument panel lamps dimmer switch input
• Ignition switch headlight control
• Interior lamps switch input
• Key in ignition switch input
• Traction control switch input
• Twilight sentinel delay input
Dash Integration Module (DIM)
The various DIM input and output circuits are described in the corresponding functional areas as indicated on the DIM electrical schematics.
The DIM functions include the following:
• Class 2 communication requiring DIM interaction.
• Control of exterior lamps.
• Control of front fog lights.
• Control of the headlights.
• Headlamps on with wiper input.
• Hood ajar switch input w/export.
• Horn relay control.
• Interior lamps incandescent dimming.
• Low side temperature for HVAC compressor.
• Power moding control over Class 2 serial data circuit.
• Reverse lockout solenoid control.
• Steering wheel controls input.
• Storage of the clock settings and, sending a message out on the class 2 serial data circuit in response to requests from other modules.
Check the fuses, I am not sure if the 1990's had a headlight relay or not (My 1987 Cabriolet does not) but if there is a head light relay its by the battery, if there is one, put your ear down by it and have someone turn the headlights on, you should hear a click.
Also, the turn signal switch/cruise control switch, pull it forward towards the steering wheel and see if the lights come on. If the headlights come on when you pull that assembly towards the steering wheel I am thinking you have a bad headlight switch.
The clicking sound is the headlight relay / thermal limit switch -- probably faulty. The light switch operates this relay -- something could be overheating or the relay coil could be faulty and not holding the realy contacts closed. Sounds like replacing the relay would be the most likely solution.
The relay has nothing to do with the tail lights, but replacing the switch sounds like a good idea. There's a nut holding it in place, see http://www.skandix.de/en/spare-parts/electrics/switches/switch-headlight/1027524/ to get an idea of the construction. And the price. This is not worth fiddling about unreliable workarounds... In addition, if fuses 15 and/or 16 burn frequently there might be a problem with the tail light cabling.
There is a circuit breaker inside the headlight switch body. It gets weak over time and use. The breaker is actually mentioned in the owners manual. A new switch is about $75.00 at the local parts store. You must remove the front of the dash to change the switch. Mine would go off and then in about 30 seconds reset and the lights would come back on. I would be driving down the road with my headlights flashing as the circuit breaker opened and closed. New switch = problem fixed.
On some models there is a dimmer switch that says it controls the headlights. Move the switch up until it clicks, and then back down again. You may have to mess with a little bit, some switches are like combination locks. Of course, some models you can't turn them off short of pulling of fuse. And for the switch i describe earlier, it will only turn them off while you are out of a drive gear, once you shift into gear, the lights will turn back on. Merry Christmas!