Possible ground issue?

[Foxmoto28]

1994 GT 5.0 t5
Optima Red top battery, PA Performance 200 Amp alternator

So Ive been dealing with this odd voltage drop/surge for the past few weeks.
Starting and idling is normal, can turn on running lights on normally. Once I turn my headlights on or activate flash-to-pass, there's a voltage drop around 4-5 volts and RPMs surge around 200-300. Hasn't caused the car to shut off yet though.

Once this problem occurs, I cannot replicate it for a few hours.
[turn on headlights, volt drop. Turn lights off and then back on, no problem. 2-3hrs later, volt drop.]
Doesn't occur when using turn signals, hazards, or any wiper/washer mode. And doesn't matter whether accessories are on or off.

Replaced:
Main headlight switch and harness
Multifunction switch and harness
Replaced fuses and relays (to be on safe side)

Cleaned all the connections and upgraded all grounds and added some with 4AWG fine strand speaker wire.
Brand new battery with new terminals and cables. PA recommends using a #4 gauge power wire, but I used #2 gauge for insurance.

Was going to replace the ground strap that's located on drivers side, connects to frame and bolt above oil filter (2 nuts on a bolt). Not sure what this bolt goes to. Can anyone tell me if it's safe to remove.

[Image from AmericanMuscle.com]

 

[ttocs]

curious, why a 200A alt but not important.

Pretty sure the bolt your talking about is just a ground lug and no problems taking the nut off but its hard to tell from the pic. Increase the size/gauge of the wire as well to a minimum 4 awg. Welding wire is cheaper then most car specific power wires and works just as well.

 

[Foxmoto28]

Got a 200A alt because I am running electronics: HID system (theretrofitsource.com) and subwoofer (not crazy system but not stock either) and did it for insurance purposes along with doing a Big 3 upgrade (cables).

So I replaced that ground with #2 welding wire, crimped and soldered terminals. (battery was fully disconnected).
Went to drive it home and had to immediately turn back. Got maybe 3 houses away.
Received codes:
KOEO:
111-System checks OK (cooling fans)
10/-Signals to full throttle
542-FP open, bad ground or always on
543-FPM circuit shows no power
&
KOER:
177- O2 sensor not switching-Left rich
542-FP open, bad ground or always on
543-FPM circuit shows no power

Cleaned and checked connections, no change. Replaced both O2 sensors, CCRM no change.
No apparent damage to wiring or pins to O2, CCRM, or PCM.
Starts and idles fine, when I drive it I can get maybe 4 houses away before it starts to sputter and jerk. Flooring it will get me there but has horrible return idle/speed.
Battery, cables and terminals are all new and clean. All ground locations are clean and tight.
Now I cannot pull codes after the car is at normal operating temperature. Scanner will connect to system but will not self test/do anything to engine.

Removed PCM and did a visual check inside. No apparent breaks in board.
Did I fry my PCM somehow?

 

[Foxmoto28]

Also, my Ford shop manual (the one that's literally a foot thick) states that 542 and 543 codes are the Fuel Pump Secondary Circuit.
I'm guessing that the primary is the fuel pump itself. So where/what's the secondary?

 

[ttocs]

FYI - HIDs actually use almost half the current the old stock style did.

By chance is the alt powder coated or fancy looking with some kind of coating?

 

[Foxmoto28]

I figured they weren't the issue as I've had them for 7 years+ with no issues.

the alternator is standard material, no powder coating, chroming or polish.