Here's a thought.... I know that some Pioneer decks cam with an "anti-theft" feature that had wires in the harness that connected to both the door trigger and horn allowing for a 15 secind exit period. Make sure that you follow the standardized wiring.
Yellow=12volt
Red=ACC 12volt
Blue w/ wht. stripe= Rem. turn on
white wires are left frt
grey wires are right frt.
greens = left rear
purples = right rear
a solid blue wire will generally be the P. Antenna lead
(on Mazda 626's w. P. Ant.s, a relay is needed)
So making sure you have all that right..... then google for your vehicle's wiring colors....I know that the main harness under the steering wheel should have two harnesses in shny black jacketing.... in there you'll find:
BIG THICK WHITE WIRE= 12VOLT
THICK BLACK WIRE WITH YELLOW STRIPE= 12V IGN.
If you're really a stickler for having a good power supply for your deck...
(cuz we all know that the sound we hear is only as good as the source that puts it out), then wire it that way using a good clean bare metal surface for your ground.
If not, then grab a 15$ test light for "Parts-o-Rama" or whereever the heck you shop, and test all your fuses... don't forget the 7.5Amp one under the hood.
Then, if all your fuses are good make your connections systematically,
start by testing
12volt that's on all the time; connect the yellow deck wire(white with blue stripe, i think.
then turn the key one click to the ACC position, find the wire that shows 12 volts; and at the same time turn your park lights on; if the test light goes off it's not the right wire.
Do the same for the ground wire, or make your own.... i think the ground is black on the car radio harness.
Course, it would have been much less time consuming to just leave the OEM harness intact and spend the 15 bones on a car harness adapter.
If you're not color-blind, then by now you'rd be a happenin' dude.
Then, with all this time that you've saved, you could take your favorite girl to that special little dead end street where we all like to show them how to "get to heaven".
Cheers
^_^