amp cuts out at high volume

I hooked up 2 (old) 180 watt sherwood amps to 2 150 watt bass cannons. the amps are only turned up half way.  At low volume subs works fine at high volume cuts in and out.

When you say "turned up half way" do you mean the input gain control?  This is your problem.  These are not volume controls, they are to match the amplifier input to the head unit output.  The gain is set too high.  Do a SEARCH on this forum for "setting gains" to get some guidance.Support the12volt.com

How are you hooking up your subwoofer? I suspect that you have the impedance set-up to low. Be careful whose advice you buy, but be patient with those who supply it.

Yep, the pencil could be right.  You say you have one amp connected to one sub.  How are the subs wired?Support the12volt.com

You might want to check your grounds also (make sure they are grounded to a clean surface on the vehicles chassis).

the amp cut out at high volume? your saying when you put the volume up on your amp cuts out? could be you are not supplying enough voltage to the amp causing it to short. Does it blow any fuses?

cuts out with the stock radio volume, I have one bridged amp to one sub. This is all old equipment that I'm hooking up for a friend, I'm talking like 80's old. I didn't check the ohm's . they are grounded using self taping screws to the chassis. They cut in and out simultaneously. but when I hooked up a 100 watt amp it worked fine that amp just didn't have enough power to drive the sub well.