Mystery battery drain -

So the girls going over 3 batteries swap in 2 months: something definitely wrong.

The thing we checked: all interior lights are off, and all headlights are off.
Thing possibly wrong: AC relay ( manually turn off both front/rear AC)

• Things that newly installed since 2022: towing wiring hardness (w/relay) from etrailer.
• Thing that add-on since 2014 : side step with lighting. I think the electrical goes under the passenger side.

So the routine is voltage measurement (engine off =12.x ) and engine on ( 13-14.x V)=> alternator is charging !

Then connect the DMM inline, power everything off and start check for mA drain ( anything over 25mA) .


I will need to print out fuse boxes and relay diagram to start to pull out the suspected drain .

Is there a common source for the tow wiring hardness elimination?

TIA