Sounds like a short somewhere alright. I'm sure I've seen it before where someone had wired another ground into the tailgate near the button, presumably to enable opening the tailgate with a dodgy door latch..
And once the latch was replaced, it did this until the other ground was removed.
Worth removing the carpet on lower tailgate and having a look...
'06 4.2 Supercharged Black/Cream "Jess" -- Bought April 2021 (NZ)
'01 4.6 Vogue Black/Lightstone "Snog" -- Bought Jan 2012
'99 4.6 HSE Cobar Blue/Lightstone -- Sold March 2009
'95 4.6 HSE Epsom Green/Tan -- Traded June 2008