Electrical Confusion

[EnvyCrew]

03 town car. Something keeps draining my battery. Replaced Battery, replaced alternator. The car had a sound system in it. Disconnected the sound system, disconnected the radio, disconnected the climate control. Battery keeps draining. Car runs and drives, but dash lights and headlights flicker (dim and get brighter) repeatedly. The headlight rotary switch doesn’t work, but the lights stay on (low beams). Brake lights don’t illuminate when the brake is pressed. A lot of concern, multiple avenues, please help.

 

[Action]

Welcome to the LOG.

And likely there are multiple problems.
Diagnosis is needed. The tool needed is a multimeter. Don't have one or know how to use it means you are farming out the job or throwing parts at the problems hoping to get lucky.

Diagnosis questions -
How many amps are flowing after the engine has been off for over an hour? The guideline is 50 to 75 milliamps.
How many volts at the battery with engine odd and engine on?
What voltage is at the headlight rotary switch?
Generally when there is no power to the brake lights, the transmission will not shift out of park. (a safety feature. The driver's foot has to be on the brake pedal to shift the transmission) Since you did not list that, it is possible there is power to the circuit (fuse & brake light switch is good) However the electrical problem is down stream. Like all of the brake lights are bad. Or again poor or an open circuit between the brake light switch and brake lights.

Flickering lamps usually means a poor connection (or ground) or a dirty/loose connection. Because this is the "dash" or instrument panel lighting and headlights the common part is the headlight switch.
Instrument panel lights not functioning may be related to the above and only for the instrument panel lights.
No high beam headlamps may be the head light hi/lo dimmer switch.

All of the above is aggravated with a non-stock sound system installed and disconnected/removed. Plus HVAC system disconnected. Not exactly sure what that means. What part was disconnected?
Both systems have illumination. And instrument panel illumination issues are part of the stated problems.

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