Installing new head unit into 2001 mitsubishi galant es

I am trying to figure this out i had a pioneer hu installed which in order to get it to work i had to splice my 12v(tellow) to my Dashlight/dimmer(orange) and red to red to get it to work. i installed a dual HU. i can only get the radio to turn on if i attach my red yellow and orange cables ??

These are the wires that are in the harness. i got all speakers hooked up. my HU dont support the dimmer so i have that tapped off. just not making sense i have to make the yellow and orange splice together?
12V constant power(YELLOW)
12V switched power(RED)
chassis ground(BLACK)
power antenna turn-on(BLUE)
left front speaker +/-
right front speaker +/-
left rear speaker +/-
right rear speaker +/-

My recommendation is to remove the new head unit, restore the wires to their original configuration, pick up an adapter cable, connect it to the new head unit on the kitchen table following the easy-to-follow installation instructions, then reinstall the new head unit properly. The adapter will allow you to pug the new head unit directly into your existing wiring harness.

What you’ve done is called “butchering the wiring harness”. This rarely ends well. It usually screws the car up forever.