Amp Problem

Many amps have protection lights that will light up if a speaker short or unsupported impedence is detected.   Sometimes it will be a separate light, and other times it will just make the power light turn red (or green if it's normally red).

Does it cut out when you turn it up to a certain volume level?  Or does it seem to be completely random?

Without knowing the specs of your subs and how they were wired, there's not a whole lot else we can suggest to you.  Try taking a sub out of the box and looking on the back of the magnet. Usually they will tell you what its impedence is.  Also, how many speaker terminals are on the box itself? (assuming you have two subs and they're both in  one box) Usually when a box has two subs in it, there will be separate external speaker terminals for each sub, but on a few manufacturer-matched boxes/subs they wire up the subs in parallel or series internally, and run it all to one external speaker terminal.

check to see if the amp is running hot.

you can add small fans.

Big Purds,

Just for my own sake, what should the DMM reading typically be on the speaker leads? Sorry to off-topic this thread but might pertain to this issue also.

Kinda sounds like you might have a bad ground.  Make sure wherever the amp is grounded to, is a part of bare metal of the vehicle's chassis.  If there's paint there, ALL of it must be scraped off before screwing in the ground cable.

Also another possibility, check the power cable up at the battery, as well as the power cable's fuse.  Make sure everything is good and tight and that you have a good fuse in there.  Sometimes fuses can check out ok with a multimeter but behave sporadically once they're actually installed.

Again both of these are kinda unlikely possibilities, but they're definitely things you should check on before concluding the amp is toast.