2003 Mustang V6 intermittent battery light issue
Ok guys I've got a strange thing I need a little help figuring out. I usually hang out over on the classic side with my '65 build, but it's time to put an end to this problem on my 2003 mustang. Here's the facts:
- I have an intermittent battery light
- I have a stereo system
- I have upgraded to both an optima yellow top and a pa performance 130 amp alternator to compensate for the stereo system.
- I have changed the terminals on the wiring for the battery because when I swapped batteries the terminals were too corroded to use again. I have all clean terminals now.
Here's where it gets strange. For a year or so, this setup worked perfectly, no problems, no battery light. Then one night driving home, the battery light kinda flickered on, stayed for a bit, and flickered back off. Very inconsistent, this happened again about a week later. No effect on performance at all, just temporary dim lights, then back to normal.
Then the problem disappeared entirely for a couple months. I decided if it came back, I'd look into diagnosing it.
Well, it came back a couple months ago. My car started having real problems staying on when it was running, and would practically almost die if I put it into drive and tried to accelerate. If I stopped with it in drive, the engine hesitation would stop with the lower rpms back. Then before I had a chance to start getting stuff tested, one day while it was doing this behavior, the car just completely died at a stoplight. Completely dead, no lights, dash needles stuck pegged over, nothing. Jumped it, car went back to acting normal again. It also died on me going 70 on the highway one night (that was fun).
After this, I had the battery tested, it was fine (a little low on charge, but passed the load test). Tested the alternator on the car, measured correct voltages. Found that one of the terminal wires was a little loose. Tightened everything up, seemed like I solved the problem to a bad ground. Problems, battery light, everything went back to normal.
Couple weeks later, battery light came back. This time I ordered and upgraded the power lead wire from the alternator. This made a huge difference on overall power output, headlights were brighter than they'd ever been (a nice change).
Here's where I'm stumped (sorry for the long explanation but now you have the story of what I've done and how I got here). After I upgraded that alternator wiring, the battery light went away again. I don't have any more of the issues of the car wanting to die anymore, but this battery light just keeps coming and going on a whim now. When it's not on, the car runs and acts perfectly. When it comes on, I can affect the light by running on the highway at 70, clicking off the overdrive, and shooting up cruising speed to 3200 rpms or higher. Click it back on, drop the rpms, light goes away. Sometimes it stays off, sometimes it comes back on. Sometimes this rpm thing doesn't do anything to it at all. Again, very inconsistent.
Last odd thing - when the light is on cruising the highway daytime, the car acts perfectly normal. Slow down for a light and drop the rpms to idle, and sometimes the light stays on. Other times, the car seems to get a really rough idle for a couple seconds (like the drivetrain is shuddering), then when that quits, it returns to a normal idle and the light disappears. At night with the added headlight load, it does the same thing, only my lights are really dim until I slow at a light and it does this shudder thing, then all of a sudden the lights are bright again and everythings normal. This shuddering thing is an every once in a while thing.
So, any suggestions on things I should look at? I just want this battery light to go off for good.
2003 V-6 - the usual bolt-ons. Traded for 2012 V-6
2012 V-6 - premium "Pony Package" edition. Leased, so no mods. Traded up for 2013 5.0
2013 5.0 - premium package, visual mods for now.
1965 coupe - Born - straight six standard issue
Now - 5.0 motor, T5 tranny, R&P, full length subframe connectors, Caltracs draglink bars, hedman headers, disc brakes, MSD 6, paxton supercharger, and probably a bunch of other stuff I forgot to mention. It's loud as hell, and my new toy