Just went through the post that was up about a week ago that Mike H. started about his C70 and the dimming lights problem... I too have a similar problem, but i fear it is much worse.

Using any electric device in the car when the headlights are on cause dimming. Both on the outer lights + the interior ones. Yes, i do have 2 10' subs and a large amp... But it will do the sam,e even when the system is off - Is this normal? Probably the most noticable is raising or lowering the windows... I can say easily say 20%-30% of the lights all around are dimmed down. Power Windows, Sun Roof, locking/unlocking doors, adjusting seats, the list goes on...

What can it be? do i need a larger cap? The battery is approaching 2 years old now. Oddly enough, when the bass is set high and bumping hard, not nearly as much power is drained then that from the windows, adjusting seats, etc. VERY ANNOYING. Help - Thanks

---alex

Do the lights get brighter when you rev the engine? I'm pretty sure your sound system isn't causing the problem. How do I know? Because from our description, I'm running a LOT more power through my system, and it isn't causing any problems. If your lights get brighter when you rev the engine, I'm willing to bet it's your battery.

Ok, i just went out and tried Revin' the engine while using some elecrtical components... And same thing. idling around 1000, Revved to 2k and a bit higher, same result - still have dimming. Tried several times. I dont understand.

I think you misunderstood what Sin suggested. Let me try to paraphrase:
(1) Start the car and let it warm up for a few minutes (to recharge the battery).
(2) Idle, in Neutral or Park; lights ON, all other accessories (like radio, A/C, rear defrosters, seat heaters) OFF.
(3) Now, rev the engine to 1500 RPM (approximately).
(4) Do the healights become noticeably brighter (compared to the brightness at idle)?

If yes, I agree with Sin's assessment that either the battery is failing, or, one or both of the battery cables are making poor connection. I would list the likely causes in the following order (of likelihood):
. Poor cable connections; check these first. If you can move the battery post clamp by without any tools, it is clearly not tight enough. They often loosen over time.
. Dry battery (is this the original factory battery? Has anyone ever checked or added water to the cells?) Even the "maintenance free" batteries sometimes need water added.
. High battery internal resistance at one or more cells (the beginning of the end of life; battery shops can measure this).
. Loose alternator belt (slips under eletrical load, resulting in battery undercharge)
. Failed rectifier diodes in the alternator (also causes battery undercharge)

Get the voltage checked on your battery.
Your trunk light might be staying on when it is closed, have it disconnected.
It could slowly be killing you battery.

Have your delaership check and most likely replace your alternator and battery under warranty if it still has it.


In the first 1 1/2 of my car i went through 3 batteries i think and finally they disconnected the trunk light and replaced the alternator and everything worked fine.

Next problem was dimming from the amp.
I also have 2 12"s and a large amp around 800. Got a 1 farad cap and it helped. The caps make sure your amp's power does not drop below 12.6 volts. Get a 1/2 farad for smaller ones.