Power 'cuts out' intermittently - WTF??

[jrobie79]

1991 318is

Audio Setup:
Class D 1000W Memphis amp - powering Fi Q 12" Sub
Class A/B 250W Orion Amp - powering two PPI-365cs components
2 gauge amp power wire/ground wire
Pioneer DEH-80prs deck, internal amp turned off

When I'm driving I notice (fairly frequently, couple times on my hour commute to work) the head unit will "shut off" and I noticed the Anti-lock light light up on my instrument cluster for a second.

When this happens it cuts out the bluetooth connection from my deck/phone and I have to manually reconnect. I also noticed the headlights, and even the interior lights, hazard button, defrost button, cluster lights, dim with the music, even when there isn't much bass.

I upgraded all the engine grounds, chassis grounds, to 2GA wire and copper lugs with good clean connections.

Is this a battery issue (exide from Advance Auto) or alternator? The alternator belt is sufficiently tight, so I was thinking possibly the alternator itself as it happens when driving. Not sure if I have a 70A, or 80A alternator but I saw a 90A alternator available. I'm going to upgrade the alternator power wire when I have a minute, but if I need to replace I'll definitely add a thicker wire when its all apart.

[Nick_318is]

Sounds like a charging issue, I would guess alternator. You could have the battery tested and rule that out.

[monty23psk]

You can also have the alternator tested, just need to take it to Autozone or something like that. Did this start to happen out of the blue? Was the sound system installed recently? Maybe a bad connection behind the radio area.

[jrobie79]

Did some more digging, it looks like the actual battery terminal is making intermittent contact. I tried starting it and all the lights lit up, however it wouldn't even crank (no clocking sound either). I went to the trunk and jostled the battery cable and went back in and it started right up. I'm gonna clean all the power/ground connections this weekend, starter, alternator, battery, junction block etc, and change the battery (probably optima yellow top) and see what happens. If it still occurs I'll diagnose the alternator and go from there