I would suspect that if the universal switch has a dome light position in conjunction with the dash light dimmer it would supply power, not ground. A multimeter reading will tell you.

You may need to use a toggle switch to ground the dome light.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.