Strange Plug, purpose???

mleads310

GreatGrady Captain
Joined
Apr 6, 2016
Messages
283
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Location
Brooklyn NY
Model
Sailfish
Removing my 05 f250’s (unfortunately had a hole above thermostat housing and by time I realized intake ingested water and hydro locked) mechanical controls , installing 08 f250’s with DEC. I was removing old harnesses and
I came across this single plug that was connected to the port motor and runs back to the battery switch (1/2/both/off). I’m kind of curious what the purpose of this plug was for and why it’s only hooked up to one motor and do I need it going forward with a newer install?

Any help is appreciated
image.jpg
 
Looks like the battery charging wire for a second battery.
 
Would there be any reason someone would hook this up directly to the on off battery switches on a sailfish?