2000 montero head unit issue

Hey all, I have just gotten a 2000 Montero Sport, went to put my system in and I hooked up the new stereo with the wiring harness for the vehicle. When I got it all hooked up there was no power whatsoever, so I plugged the stock radio back in and it makes a small buzzing sound for about 2 seconds and then no signs of life after that. It has the alarm system on it and whenever you take a battery terminal off and put it back on you have to put a code in the radio to get it to work again. I don't know if that has something to do with it or not.

Ground the black wire of the radio to the chassis of the vehicle.

so just ground the stereo to the car and leave the ground coming from the car taped? Is that going to bypass that security code? I took a multimeter to it (mind you I don't know how to read it) and when put to the red and yellow it changed quite a bit. I did get the factory radio to work again but want to get this figured out so I can get a clean swap out of the head unit before I go running everything for the amp.

to make the new radio work you just need to verify that you have 12 volts on whatever wires from the car the red and yellow wires are being hooked to, and you need to verify that you have a good ground connection on the black wire. usually a good idea is to ignore the factory ground and connect the black ground wire of the new radio directly to a solid metal brace behind the radio this way you know that you have a good ground. also sometimes there is no ground wire in the factory harness because the factory radio can use the antenna as a ground.

to verify the voltages on the red and yellow wire you would just take the black test lead of your multi-meter and connect that to the same spot you plan to connect your ground wire to, then use the red test lead to test each wire for the proper voltage, between 12 volts and 14.4 volts with the engine running, anywhere in that range is acceptable. the red wire from the radio should only have power with the key in the on position and the yellow wire should have power at all times.

as long as these conditions are met then your new radio should work, or at least turn on.

I ground it to the car and sure enough it turned right on, thank you very much for your help!!