amplifier shuts down after minimal use

I recently purchased a Punch XLC RFP2812 Woofer, a Punch 600 a4 amp, and a Pioneer DEH-P520 head unit and installed it all into a 2002 Ford Focus ZTS. This is the first time I've ever installed any sort of sound system in a car, but I managed it after some tweaking and troubleshooting; however, after trying to use the new system for more than a few minutes the amplifier shuts off. I'm fairly certain the amp is shutting itself off, but not really sure as to why it is. I've read through the manual on the amp and it mentions that due to its heat sync it shouldn't overheat at all as long as it is not installed upside down (which it's not).

I'm thinking it's somehow due to the wiring or a problem with the electrical system somewhere. During the few minutes the amp is in operation before it shuts itself off the lights in and out of the car dim anytime there is a large "thump" coming from the subwoofer.

Currently it's wired with a 12 foot 5 awg power wire (with a 100A fuse) coming from the battery to the distributioin block, then to a single 4 foot 9 awg cable wired to the amp. The amp is grounded inside of the trunk using a 6 foot 9 awg cable with the loop on the end drilled into the roof of the trunk. The amp is wired into 2 channel mode, with both channels wired directly to the subwoofer. Reading through some of the information around here it looks like it may be due to the relatively high gauge for the power cables considering the overall length, and the length and high gauge of the ground cable.

I'm planning on cutting back the lengths on all of the cables, and reducing the settings on the amp and head unit to minimize the bass just to see if I can use the amp without it shutting off at all. Installing a lower gauge cable really isn't possible, as the input on the amp will only accept a 9 gauge; however, if I need to reduce the size of the B+ wire that's entirely doable. I was also wondering if it would be possible and/or beneficial to wire the amp as one channel by bridging it in a way similar to configuring it for two channel operation. Also is grounding it to the interior of the trunk sufficient? It's currently screwed into the ceiling of the trunk, which is some pretty thin metal (probably around 1/16th of an inch) in retrospect to something like the exterior the car.

Any other suggestions for how I could solve this would be greatly appreciated.

Specs:

Amp test impedance: 2 ohms

9 gauge, 5 gauge.... where did you get your cable? You also mentioned a dist. block yet only 1 amp....or am I not reading correctly.

6 foot ground cable.... fix that.  Where is the "roof of the trunk"?  Also, how did you bridge this amp? It's a 4 chan. how did you make it a 2 chan. ?

You're reading it perfectly. I bought a wiring kit that had everything you would need to connect the amp to the head unit, battery, and to ground it to the car. I tried using the straight 5 gauge cable to connect to the amp, but the amp's wiring port wasn't large enough to fit it in; so I had to use the distribution block to connect the power wire to the amp.

The roof of the trunk is a pretty thin shell inside of the trunk, separate from the main body of the trunk.

I bridiged according to the instruction manual as the amp has its own two-channel mode, but I was wondering if I could use a smiliar method to bridge it into a one channel mode and only send one set of speaker wires to the sub.