subs cut out only

Hi, I recently installed 2X TS-W307D4 pioneer 12'' subs powered by a Clarion DPX1851 mono block. 4 gauge running length of car to a distribution block were it is split into 2X 8 gauge one going to my DPX1851 and the other running to my 4X 50W 4 channel after tuning my amp and getting it all going i have run into a problem i turn the volume up to about 25 out of 33 on the head unit and on the hard hitting bass songs after a little bit of time the subs only cut out and the amp goes into safe mode but my speakers keep on playing. Previous to the distribution block the 4 gauge was running to the amp and it was running fine is this happening because there is a lack of power? My car is a 1986 Holden VL executive (Australian)

sounds like you have some bad voltage drop...You need to upgrade your big three and alternator.

how did you wire the subs?Jon

The subs are wired parallel i think a friend installed it by memory it is (positives linked), (negatives linked), link a positive and negative between the subs and so on, What gauge is recommended to upgrade my big 3 to and roughly price (and is it doable without replacing alternator)