Voltage Drop At Amp, Alpine PDX5

2001 Ford Econoline with 5ch system (Sony HU -> Alpine PDX5 -> 4 mains & 1 sub), fairly simple setup. For some reason the amp's been cutting out for a few months. Seems random but then will sometimes occur when hitting bumps in road. Tried 2nd amp, same deal. Replaced remote wire, same deal. Re-grounded amp, same deal. When the sound cuts out the amp's actually shutting down, indicator lights turn off.

I've found two wiring gremlins so far - one of the mains is showing 32 ohms (should be 4). Has low output at low volume but kicks into gear at higher volume & matches others. I'm thinking wear & tear on that. It's def not shorting tho.

Second gremlin, amp B+ clocks at 9.3v while it's 14+v at B+ underhood. This leads me to believe amp is shutting down due to low voltage. But why on Earth is the voltage low? 4g cable from battery to fuse, I get 14v at fuse on downstream side. From there it's a solid run thru firewall, then under driver's seat to amp.

Only exception is a remote start is tapped into 4g B+ under dash - the cut away insulation & worm in a couple of 10g wires method. If that were a splice (IE cable cut & reconnected) I'd suspect that spot went bad. But it's not cut, the starter wires just wrap around & thru under tape & zipties.

Any ideas other than simply replacing 4g B+ run? That's likely my next step but I'm truly baffled why I'd see a voltage drop instead of a full cutout. Anyone dealt with that before?

SOLVED!! Probably because I posted it here...

At the battery underhood (7.3 powerstroke diesel with multiple batteries) there's a brass lug pressed into the soft lead of battery terminal. The 4g cable is att'd to that lug. Evidently the lug's fit in the lead terminal has become loose & wasn't producing a good connection. Pressing it in & stabilizing with some zip ties brought the amp back to 14v.

My guess on low voltage, probably very low current amount was able to 'enter' the 4g wire given the poor connection. And the relatively high current draw of amp relative to that connection likely led to a big voltage drop. That's my theory anyway.

Leaving this post here in case someone else has same problem. Cheers guys -