This sound familiar to anyone..Electrical Problem.

[MuMan]

Got this electrical problem that someone else might have encountered.
Every so often at idle the volts drop to 12v give or take, and the dash lights dim..well everything inside the car seems to have a voltage drop.

Sounds like a classic case of a bad battery or alternator...but not the case. The alternator pushes out around 13.9v and the battery is a new dry chemical one. You see it when the cooling fans cut in mostly, or the aircon fires up..but everything in the engine bay, including the headlights seems to be not effected... idle remains reasonably normal.
Checked earth points and connectors..
One clue I've noticed...you hear a relay cut in before it happens, and drop out when it comes good, but nothing I've noticed switches on or off when you hear the relay work??

Any ideas appreciated guys..no matter how unlikely they might sound.

[Supplanter]

How many amp hours is the new battery rated at?

[MuMan]

Not sure, around 180A/hrs I think, it's one of the dry Alkaline versions. I actually had it replaced at first because I suspected the problem was the battery.

[mmmyum]

Does your voltage change simultaneously when you signal aswell??

help me 2!!

[MuMan]

Not sure about that, haven't noticed if it does, but I'd have to check and make sure.

[bigpitty1]

What is the RPM at idle, because my stepper motor has died and I have found that when the idle hit 500rpm the voltage gauge just drops back to 12volts, check your idle it maybe too low.

[MuMan]

Think you might be on to something there..
I just replaced the stepper motor, so I'll check it out.

[MuMan]

I think you might be right, seems maybe that relay is opening the charging circuit to un-load the engine at low revs..I'd have to check the circuit diagram..but makes sense. Over 650RPM it doesn't happen..with the stepper motor replaced, it's steady on 750-800