Thread: Electrical system under powered? Dim's and drops in voltage when stopping?

Ok so here's the scoop.

Occasionally when I'm stopping with my headlights on and heat on, my car drops in voltage/power and the lights dim, blower slows down, for a sec then bounces back. Today it did that like 4 times in a row when I was pulling into a gas station. It only does it when I'm coming to a stop and never while I'm driving down the road. The car doesn't really drop in rpms (maybe slightly) so it's not like car is dying per say.

Also, I have a radar detector that turns off automatically after 6 hours. So after I've been driving (like after i got home from work) and park my car, i leave the radar detector plugged in knowing that it will just shut off in a few hours. When I get up in the morning it is off (which is normal) but when I turn my car on, it turns on (which it never used to do). My car also doesnt seem to be cranking as hard as it should. I'm guessing the radar detector is coming on because once the car is running its now getting the full 12v's which turns it on (like as if i replugged it back in). This never used to happen. I would normally have to unplug it and plug it back in so it would turn back on.

So heres the weird part. I know your probably thinking "oh he has a weak alternator or battery". I've replaced both. I put in a brand new optima red top and a 125a alternator. So ive not only replaced the battery, i replaced the alternator with a higher output one and the problem still occurs.

I have no idea why its doing this.

Additional information:

I have a pioneer head unit. I have a alpine 1000w amp and a JL audio 10" sub w/ 2 farad capacitor. I've had the system in the car for a couple years and it never did any of the goofy things until recently. The capacitor always reads really low voltage when the car is off and has been sitting for awhile. Like low 10's. Sometimes its so low it wont even be on.

So heres the question. Why is this happening? Is there something that controls the voltage output from the alternator? Could I have some unknown draw in the electrical system that is draining constantly?

I could pull the fuse on the stereo system but I don't think its going to change anything.
I have also cleaned up all battery terminals and cleaned up all grounds.

This is really starting to piss me off and would appreciate any information or help that you could provide.

mine does this to, and i got about the same setup, subs, hids, heat all that stuff and i also have a battery with a dead cell, and a weak(factory) alt
when mine does it, the dash lights go real dim and the left headlight flash's(hid) like its bout to go out, but it only does it when the rpm drops under 900, even when the cars warmed up
im checking all the ground first then doing the 3 big upgrade in a couple weeks
so ive sub'd to see what other say

I did notice some corrosion under the boot of the positive terminal. I'm going to take the boots off and clean them up and see if that helps.



Anyone else have some insight?

I had that on my 03. The only thing that fixed it for me was the "The Big 3". :/

EDIT: In fact, what helped the most was running a line directly from the alternator to the positive terminal at the top of the fuse box under the hood.

Just wanted everyone to know that I did the "big 3" and it fixed my electrical issues. I think it was a combination of corrosion and the weak job GM did wiring these cars. Now that I've run a power wire from the alt to fuse box, and fuse box to battery. I'm seeing much higher voltage and no more dimming of lights from my stereo even with everything on.


Hope this helps !