I wouldn't do that. There are certain things that the player does that expect the two power inputs to be separate. You'll get various strange behaviors from the player. Not the least of which is that you'll get a nasty speaker-damaging "pop" each time you turn off the ignition or pull the player from the sled. Also, if you ever sell the player to someone else, then it won't work right for them. Finally, doing work inside the player is much more risky than doing work to the sled and wiring. The player innards are harder to fix if you mess it up.