Final answer:
Providing auxiliary 12-volt power during vehicle service maintains memory settings and PCM parameters but does not pose a risk of PCM damage. The risk is from improper procedures or electrical issues. Overloading a battery with devices can lead to dim lights, indicating a voltage drop.
Step-by-step explanation:
When servicing a vehicle, providing auxiliary 12-volt power to the vehicle before disconnecting the 12-volt battery helps with various functions. It can keep radio station presets stored in keep alive memory (KAM), maintain automatic power seat-position memory settings, and ensure that engine operating parameters are maintained in the PCM (Powertrain Control Module). However, it does not pose the risk of damage to the PCM; this is a misconception. The risk of damage might occur if proper procedures are not followed, or if there is a short or voltage surge, but not from just providing auxiliary power. Regarding battery connections, if you connect an excessive number of 12-V lights in parallel to a car battery, the lights will be dim, suggesting that the battery's output voltage is reduced due to overload. This is an example of the consequences of an electrical system under excessive load, which is not directly related to the maintenance issue described above but shows the importance of understanding electrical systems in vehicles.