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Discussion Starter #1
Calling all mustang lovers! I am in desperate need of help. I have had a on going issue with my 2000 GT 4.6L mustang for about 4 years now and I can't figure it out. All the electronics in my car are stock. I have not added a new cd player or subs. The only after market I have added to my car is a cold air intake and short throw shift. I've tried three different mechanics all of them are stumped. Lets start from the beginning. When i first purchased my car a few years ago, I took the guys word when he said everything was good in the car. Yes I know, HUGE mistake. So anyways I later found out after driving my car consecutively for about 30 minutes to 1 hour, my head lights would start to dim and my rpm gauge would start jerking up and down ever so slightly and you could feel it while you drove. Also when I attempted to do a burn out or just do a fast take off in my car it almost kill my head lights completely and almost made my car stall. So soon after, I brought it to a mechanic and he hooked his computer up to it to diagnose the problem. He came to the conclusion that my A/C was broken and was drawing to much power from my car and that my alternator was faulty. SO he unplugged the A/C and to my amazement the rpm gauge stopped jerking up and down. So I took it for another long drive and soon enough my head lights start dimming and flickering, but not as bad as it was before. I could still do a burn out now and not stall my car. On another note I got in a car accident with a deer and had to get some body work done. While at the shop they topped my A/C with free-on (not sure how to spell that) and it fixed the issue with my A/C. I tried talking to other mechanics, people I know, and posting threads on the forums here trying to figure out why my head lights are dimming. Someone told me oh its a bad battery most likely because when it got cold out my battery started dying. So I got a new battery and still the same problem. As winter came along my car stopped doing it as quickly as before and it would take a longer drive to make my head lights dim. I brought it to a mechanic because someone also said something could be drawing power from my care while its off and killing the battery and making my head lights dim. The mechanic concluded that there was no extra power draw. So here I am not a inch closer to solving it still. The problem was that it was hard to show a mechanic what was going on because you could only see it happen when it was night and all mechanic shops were closed. I happened to get my head lights to dim and stopped at a mechanic shop right as they were closing. I said look, do you see my issue here? The mechanic brought out his tester and over loaded my battery and alternator trying to see the issue that was causing it. He said it seemed like my alternator was over heating and not producing the amp output my car needed. I thought oh that makes sense because when it was colder out my head lights would not start dimming as quickly. I went down to my local auto store and bought a rebuilt alternator for my car. I quickly swapped it out with my old one. Tested it and was showing 14.3 volts which was good. I drove it for a while and my battery light came on. The next day I went to drive it and I could see my battery gauge dropping dramatically and went straight to dead. I just barely made it to my drive way and my car completely stalls on me. I jump started my car with my girl friends and unhooked the cables. I took out my multi-meter and tested it. The volts were reading 8 volts then dropped to 6 volts and my car stalled. So I'm thinking okay, must of got a faulty alternator. I found a really well respected guy in town who rebuilds alternators. I brought him my old alternator and got it completely rebuilt. I installed it and I have been driving my car for three days now, my battery is not dying. But guess what? My head lights still dim. So this where I am now and I really don't no what to do. I don't have a few thousand dollars to just throw at my car and tell a mechanic to figure it out. So if anyone, please anyone, has some insight, I beg of you to let me know. Any comments are greatly appreciated. Thank you. cloud.gif

- Also I forgot to mention that at the same time my head lights start dimming, my high beam switch stops working to and the only way to get my high beams on is by holding it on by pulling it towards me and holding it there.

- Wiggling around the wires to my head lights does not cause them to dim or do anything. Someone mentioned it could be a loose wire and I can assure you its not.
 

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I could be totally wrong here (what a start, right?), but your issue reminds me of some problems I had with an old Beretta I owned many moons ago. A new battery and three alternators later, it was a faulty battery cable.

Have you replaced this?
 

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What is the condition of the grounds around the radiator core support?

How about the battery terminals?

It would also help if you posted the normal engine on voltage at the battery when everything was OK and again where there's a problem.

Bottom line. Today's cars simply will NOT run right without a strong battery and charging system.

Check out this thread regarding cluster PC foil trace repair.

http://www.allfordmustangs.com/forums/v6-tech/304608-my-odometer-goes-off.html#2657361

How could this be related to your problem? What if the dash battery charge light should be on and isn't? Well this is one possible cause.
 

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Discussion Starter #5
Battery terminals are good.

I have had this problem with my car since day one.

It's the right battery and alternator for my car.

All my dash lights come on when needed.

I'll check my ground wires.
 

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Maybe your mechanics checked the grounds, maybe they didn't but you should clean them all just in case. There are two that connect from the negative battery terminal unto the frame, there is one under the car below where the crankcase pulley is, and I believe there is one around the power steering pump/reservoir though I don't remember if it is visible from the top or bottom.

Clean them all to ensure that your problem isn't due to inconsistent voltage from a bad ground.

Verify every single fuse on your car is the correct one and is functional. I have personally purchased many cars with odd electrical behaviors and the problem was 20-40% of fuses were wrong. My gt was no different.
 

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Did you check the connection at the Junction Box? (for 12+)

Typically this gets corroded often.

Cheers
-Matt
 
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