This is going to be a learning curve. You already know about the TCM and ECM. Your car also has a DIM (instrument cluster), ABS module (why they don't have a --M for that), and a little known CEM.
The CEM is nothing but a buss, it routes communication between all of the computer boards. If anything goes wrong with the CEM, the other computers do not get the required info needed to make adjustments to speed, rpm, temperature, etc. Sometimes the DIM is affected, like no speedometer/odometer and when that happens the car will shut down and become road kill.
The problem with the early DIM and CEM is the heat sink is not large enough and diodes melt. It has nothing to do with 'lighting' and everything to with communications.
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My back feels better when I sit in a Volvo seat
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