amp cutting out, annoying

I have an '05 dodge ram and the system cuts in and out when its cold outside.I have installed many systems and have a good idea of what I'm doing.Anyways,as I said,when its really cold out,say -15 celcius,or colder,my amp cuts out whenever I hit anything that takes power.Eg.power locks,windows,turn on headlights,even turn the steering wheel or hit the brakes.Once the vehicle warms up,or if its warm outside it doesn't do it.The amp was brand new when I insalled it last fall [its a Focal 5-ch].I used good quality #4 power & ground.The power wire goes staight to the batt.The ground is attached to a bracket bolt on the rear wall of the truck [scraped the paint off].The remote wire goes to a new Alpine h/u.I don't know what its problem is.If anyone can figure this out please,please let me know.I'm stumped!!Maybe I'll just have to move somewhere warmer!!

p.s. sorry about the long post but I wanted to make sure I explained the problem acurately.  

Not necessarily, I prefer to make my own ground as I have found factory bolts and brackets to be inferior grounds. Try regrounding  and then meter your ground, I would also suggest reading the post about proper grounds in the sticky's above. Hope thi shelps ya out.

I would also get your battery load tested it free pretty much any auto parts store.

The best way to check if the power wire or ground is the culprit is to check voltage with a DMM, afterall you can't see electricity with your eyes..the meter will see it and does not lie, of course if used correctly.

Set the meter to measure DC voltage, place the negative probe on the ground terminal AT the amp, and the positive probe to the battery terminal AT the amp. See what you read when it is cold. If it is reading low take the meter and check the reading at the battery itself. If the reading there is normal you know you are losing the voltage somewhere in the wires. If the reading at the battery is also low, you know the problem is the battery and/or charging system.

If you suspect the ground is poor set the meter to resistance and place one probe to the amps ground terminal, and the other probe to a good known ground spot (like the chassis) or to the battery negative itself. The reading should be at or very close to zero resistance (a little resistance is to be expected). If you have a high resistance reading (a couple of ohms or greater) check the grounding location and the ground terminal (might be a bad crimp) or require a different grounding point.

If everything checks out good you might have a defective amp that simply doesn't work right when cold, it is a possibility as well but use the meter to eliminate all the guess work.

It also can't hurt to check the voltage of the remote wire at the amp when cold as well if everything else checks out ok.

Post back your readings if you still can't figure out the problem and we can guide you from there.

Good Luck.

Thanks for the help,The hard part about testing this problem is that it only does it when its really cold and its hard to get at my amp as I have to remove my rear seat[quad cab dodge].By the time I get it in the shop and get at my amp, it works fine because it had time to warm up.

p.s.To measure my ground I unhook the power at my amp first ,right?