yardost

My '99 Mustang GT Convertible has been having some sporadic and odd issues. Symptoms I have noticed so far:
- Whining noise from the speakers when engine is running
- On occasion, opening the passenger door would cause the interior light to stay on even after the door is closed. You can open and close the door again, turn the car on and off or try combination of things but the issue stays. At times, it goes away the next time you start the car, other times, it stays that way until the next symptom below shows up. While the light is staying on, after shutting the car off, when trying to activate the alarm, the car gives a quick double honk which I assume means the alarm is not engaging.
- Turning the key makes all dials go to max and back, after which the engine does not turn. All lights work, battery checks out ok but the starter would not kick in.
- Unhooking the battery cables and reattaching them fixes the issue and also fixes the interior light issue mentioned earlier.

Nothing complicated with the wiring except an aftermarket stereo using a wiring harness. The whining from speakers started after the new stereo. the other symptoms have been there all along.
Please help.

WhiteFoxGT

The whining from the speakers is RF interference. Did you use an aftermarket amp along with the head unit? As far as the gauge sweep, thats a sign of a bad battery. If the voltage to the GEM module drops below a certain point, it will do funky things and act up. I'd say replace the battery and start there.

mustangman281

Yup the whinning in the stereo is RFI. Check the wiring and the capasiters on the front of the engine. If everything checks out then check the COPs and twist the wires up to reduse RFI.

Your battery is dying probably because of the light. FInd out what is causing it then replace the battery.

yuengling910

the sound through the speakers could be a bad ground at either the head unit or the amp as well as interference.

Brute03

the sweeping gauges doesn't necessarily mean a bad battery, it could very well be a bad ground. a while back i was having the same issue because my neg. terminal was loose and corroded. i replaced it and the problem went away

zanypunk

Yep it sounds like a bad ground. Test it with your meter. Your ground should be zero with the load, if you find a number then you have a bad ground. Make sure to use a 4 inch gauge because with a smaller wire the system will only be holding a lot of resistance. I'm also thinking of something else but try this first.