Headlights dimming/power loss?, Headlights dimming after brakes applied or blinker... Options

[Betta-J]

Honestly, I am stuck on this issue for quite a while.
I initially thought it was the batter or the alternator.
I got the battery tested at Walmart as that is where I bought the battery.
They told me the battery was low but the cells were ok.
I figured it was the alternator. I changed that out.

The other things I changed out were the sparkplugs, although I could not get one of them out and I think it's misfiring.
I'll have to take the head cover out and unscrew the pipes, as the sparkplug that I couldn't get out, will have to be taken out this way due to the nut part being gone(?). I can't really see.
I've changed the water pump and the timing belt at this time too.

The symptoms:
1. I apply the brakes and the lights go dim.
2. I don't have a hard time starting the car, but sometimes I feel that during idle it may go off...it feels weak.
3. The alternator I bought was tested and was ok.
4. I hear my misfiring slightly--but I know which one it is; I just don't see this as the problem, but who knows.
5. I have my hazards on or my blinkers, and it dims as well.
6. When I lock or unlock my car (security keyless), sometimes the horn sounds weak like there's no battery. Sometimes it's strong.

I would appreciate any insight or help on this.
If you need more information to diagnose, just ask and I will try to observe more symptoms.


Thanks in advance.

Betta-J

[VavAlephVav]

The other things I changed out were the sparkplugs, although I could not get one of them out and I think it's misfiring.
I'll have to take the head cover out and unscrew the pipes, as the sparkplug that I couldn't get out, will have to be taken out this way due to the nut part being gone(?). I can't really see.

a lot of times what happens with cheap spark-plug wires is the connector boot comes off the wire and stays on the plug, which blocks the nut so you can't unbolt the spark plug from the motor.
Last time I finally broke down and bought some nice Denso plug wires. (from Rockauto of course) but you'll need to look down there with a flashlight and see the black rubber piece still on the plug, most likely that's the deal.
What you need to do is get a small hook/pick set, you can get a cheap one from harbor freight or wherever you can in your area.
http://www.harborfreight.com/4-piece-pick-...-set-66836.html

something like this one you can use to reach down in there and grab ahold of the rubber boot and pull it off the spark plug so you can get the plug out.
The deal with plugs is Copper is the best conductor of electricity. Other materials like the Platinum or Iridium just last longer so you don't need to change but once every 100k miles or so.
But the plugs on this thing are so easy to change there's no excuse to not get Copper and change them once a year or so. And Coppers are <$2.00 each. Again I buy Denso Copper Plugs and Denso wires on Rockauto for super cheap.
And yes you should always use a Denso or NGK those are like what the car was designed for. Autolites have a completely different seat and seal they just don't fit right.