2008 ls MGM w/ multiple issues
 

So I received an 08 MGM from my grandfather as a hand-me-down, but she came w a few issues.
These happen all at once, and sometimes randomly goes away:
- dome light remains on w door open or closed
- the tire monitor fault comes on, although pressure is fine.
- oil monitor system activates and says to change oil. When resetting oil system, it will only reset to 60%
- door lock buttons dont work (window and seat controls ARE working)

Anyone have any idea what could be going wrong? Have had it to a shop and the guy said it was out of his league.
I have a feeling it has to do w the giant module within the door panel. That all the wires route to, but dont want to shell out the $ for nothing.

Multiple issues
 

Here's a quick "check" on the overall condition of your electrical system:
Disconnect the battery -- NEGATIVE TERMINAL FIRST, THEN THE POSITIVE.
Leave the battery disconnected for ONE HOUR.
Re-connect the POSITIVE cable FIRST, then the NEGATIVE cable.
While the battery is disconnected, check the water level in each cell, clean the battery area with baking soda and water, and rinse the area when finished.
If you have a volt-ohm meter, check the battery voltage -- should be about 13.8 volts with engine running.
With the battery in top condition and the computers re-set after the battery disconnect, your "issues" may clear up.
On the Dome Light -- Push "IN" the headlight switch knob to turn the dome light "OFF".
The headlight switches on the Merc Marquis are complicated and expensive -- When my switch went bad, I got a brand-new aftermarket switch from Amazon,
and installed it myself. Looks great and works perfectly.
Lemme know what you find out !!