So I have a 2004 regal ls, I bought without a radio in it. I've had a kenwood kdc-bt310u sitting in the box for awhile now and and can't figure out which wires to put together. The big connector that went into the stock radio is gone, cut off. The smaller one is still attached though. Is it possible to hook it up by splicing the wires together without the harness or whatever? Sorry but I'm a total noob at this. Any help would be much appreciated!

Sucks that somebody had to cut that off, a cheap wiring harness connector was all they would have needed.
Let me see what I can dig up.

Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black/White
Car Radio Illumination Wire: Gray
Car Stereo Dimmer Wire: Dark Green
Car Stereo Antenna Trigger: N/A
Car Stereo Amp Trigger Wire: Violet
Car Stereo Amplifier Location: Mounted under the rear deck.
Car Audio Front Speakers Size: N/A
Car Audio Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue

This should be the right diagram, I am pretty sure from 1994 to 2004 the wiring was the same.



Have you bought the wiring harness that you would need if the original connector was not cut?
If not I'd get that, and get an end to replace the original that was cut, you will want to this.

And the connector that goes from that connector above, to your radio.

I suggest when joining the wires that you soldier them, and slip heat shrink tubing over them, you could try to crimp on some butt connectors, but soldier and heat shrink is the way to go, have to be careful though, because I cannot imagine soldering that connector back on will be easy, so you may be forced to go with 22/18 ga vinyl butt connectors, just be sure to crimp them well!
The Install Bay RVBC Red 22 18 Gauge Vinyl Butt Connectors 100 Pack | eBay

First, that diagram is for a Bose radio. Mine is not. Second, there is no switched 12v. I've found the wiring diagram for the monsoon premium sound system, but my car doesn't have that and it shows more wires than what I've got. Will the head unit still work if I don't hook up the switched 12v red wire? I read somewhere that someone did but to turn off the head unit they had to detach the faceplate

looking at the service manual for that, all those are right(illum, always on power, ground, speakers). the only thing is the car has no key power, gm does it by a wake up command through the network. the aftermarket hu needs this so you have to wire it to a RAP(retained acc power) fuse. take a meter and find a fuse that is not on with the door open and when you close the door and turn it on it stays on till the door is opened. then get a "fuse tap" and wire your keyed input power to that. parts store should know what you need if you tell them that, but there are different sizes for different fuses

But will it still work if I don't hook the RAP up? I've read that it should, but I would just have to detach the faceplate to turn it off

no. to get it to turn on and off you need to wire it to something. not a big deal. the manual says the only thing on rap in the interior fuse panel is the 30a circuit breaker labeled "pwr wdo". take that out and go to the parts store and tell them you want a fuse tap for that size and run the keyed wire to the tap.

I was just providing a diagram so you would know what the wires that were cut went to, that may have been for a Bose Radio, but the factory harness wires/colors should be the same.
I still say getting the two harness connectors I suggested, and splicing them together as I suggested is the best way to go.
You could cut the ends off of the radio, and use butt connectors on the two bare ends, but that is not really the way a professional installer would do it, I tried to suggest the best way, sorry I forgot about mentioning the RAP.
Hopefully everything else I provided helps you get it done.

Sorry if I was an a**hole, I've been so frustrated with this. I can't find a fuse tap that'* rated for 30 amps. All the ones at AutoZone and advanced auto parts are only ten amps. I just want to get this done and over with, is it possible to attach a wire to the under side of the fuse that is RAP run it to my radio? I know I can get to the back side of it.

It doesn't have to be wired into RAP. Just find a power source that'* switched via the ignition switch you and will be fine.

I can't make heads or tails of wiring diagrams. I'm a total noob at this.