davesexplorer said:
how does the battery make a difference since batt = 12v and alt = 13.5-14v
you are not getting any power from the battery unless you are overdrawing the alternator... a new battery will not solve your alternator problem...
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He is overdrawing the alt at idle, that is why his old battery is probably dying since I assume it has been deep cycled too many times and is not charging to it's fullest capacity. Obviously it is hard to diagnose without actually checking out the vehicle, but I would definitely suspect that the battery is on it's last legs because of weak output of the alt at idle.
yes all correct but why buy a new battery, which wont help the dimming much at all, and have it fail because of constant discharging...
The problem therefore lies in the alternator or its wiring, the dimming you see comes from all your accessories running at ~14v from the alternator, when you overdraw the alternator your accessories must then run off the battery, 12v that 2 volt difference is what makes your lights dim, your accessories are taking power away from your lights, and taking power from the batt.
So everything you said is right, but you didn't address where the problem lies, the alternator system...