About Battery Warning Light, Do You Know Something About it?

**Polo Tim** · October 26th, 2017 06:30 PM

Hello there,

I have a 2008 Mustang GT and have the battery warning light coming on and off intermittently for the past 3 months or so.

Alternator was replaced 2 years ago and battery less than 1 year ago.

Car starts up and drives just fine and never had any issues until today.

This morning when I went to put the key into the run position, I noticed that all the analog dials swept to the max position and back to zero. Car starts up just fine. I drove it about 1-2 miles and parked.

Came back to the car, key into run position and the dials swept through again. But when I tried to start, the starter clicked and loss all power to the car. No dome lights, no trunk lights, nothing. Like there wasn't a battery in the car.

Popped the hood, and disconnected the negative cable from the battery. I reconnected the negative cable to the battery and the power came back on in the car. Key back in run position, dials sweep and car starts up just fine.

Drove another 1-2 miles and parked for about an hour. Went back to car, key in run position, dials do not sweep and starts up just fine. Drove 3-4 miles and the battery warning light came on for a bit, then went away and came back on again.

From my Google search, I found a lot of people saying to "check the grounds". I really don't know what that means.

Any ideas? Help! Thanks a bunch.

**oj88** · October 26th, 2017 07:09 PM

This is new. No CEL?

Anyway, I'm not going to pretend that I know everything but I would start with the obvious. Something seems loose. Try to remove both battery contacts, clean them thoroughly, and reconnect them firmly. Though, read the manual if disconnecting the battery is advisable as certain things like the security system of the vehicle and/or radio might kick in or at worse, the procedure might reset certain settings to default.

If the problem persists, I suggest you bring it to Ford. If it's still under warranty, you've nothing to lose.

**yebo** · October 26th, 2017 09:38 PM

parang symptoms ng low charge. do you have a voltmeter, preferably a digital one that can measure to 0.01 volts?

test the voltage across the battery terminals and compare to the voltage measured across the battery connectors. if the voltage across the connectors is lower the battery connections both positive and negative may be loose or needs cleaning. voltage must be around 12.6V.

if battery voltage is ok then test the voltage with the engine running. if it is less than 13.8 volts then the alternator or diode may be faulty, or connection to the alternator loose, causing battery not to charge properly.

**kinyo** · October 26th, 2017 10:34 PM

"check the grounds" means checking connections on ground wires (wires connected to the car's metal body)

first and foremost ground wire is the negative cable on the battery ... this should connect to the car's metal body somewhere and should be really tight

another ground wire connects the engine to the car's metal body ... if loose, strange electrical problems may occur ... this wire also carries alternator charging current

most other ground wires are found inside the car

good luck

**StockEngine** · October 26th, 2017 10:40 PM

retorque those 10mm nuts ...

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**12vdc** · October 27th, 2017 12:14 AM

Originally Posted by Polo Tim

Hello there,

From my Google search, I found a lot of people saying to "check the grounds". I really don't know what that means.

Any ideas? Help! Thanks a bunch.

Check the grounds came from the idea the the earth's soil/ground is an electrical discharge point between the sky that holds the charge and the dialectic air in between.

In car's laymans term, the earth ground is the car's body chassis which is the negative potential in reference to the battery

It means that you should check the negative return path contact points of the chassis/body/electrical accessories for possible loose connection causing the error on the car's computer.

**Walter** · October 27th, 2017 07:16 AM

Possible alternator problem ...

**barako ba ma** · October 28th, 2017 06:20 PM

Check for circuit voltage drops first before contemplating of blaming and replacing parts.

Voltage Drop Test | Delco Remy Tech Tip - YouTube

**SidCoronel** · October 29th, 2017 01:24 PM

Originally Posted by kinyo

"check the grounds" means checking connections on ground wires (wires connected to the car's metal body)

first and foremost ground wire is the negative cable on the battery ... this should connect to the car's metal body somewhere and should be really tight

another ground wire connects the engine to the car's metal body ... if loose, strange electrical problems may occur ... this wire also carries alternator charging current

most other ground wires are found inside the car

good luck

Good start... To check... Look at the battery terminals, these are 2 silver studs (terminals) sticking upwards like horns, 1 has a red plastic base, the other has a black plastic base... The later is the negative pole. It will have a thick black wire attached by a metal clamp, this is smaller compared to the other stud/terminal. Trace the wire of the negative pole and it will lead to where it is attached to the car body by a nut. Check that the wire is firmly connected to the body, by slightly yanking it left to right. If the wire moves, then it's loose. Clean the connection surfaces and tighten. I personally use a di-electric grease applied on connection surfaces for better contact and surface protection against elements.

Power and electrical troubles are a pain, it's not that easy to diagnose and fix.

Bring it to your dealer, let them fix it.

**dr. d** · October 30th, 2017 01:15 AM

Originally Posted by SidCoronel

Good start... To check... Look at the battery terminals, these are 2 silver studs (terminals) sticking upwards like horns, 1 has a red plastic base, the other has a black plastic base... The later is the negative pole. It will have a thick black wire attached by a metal clamp, this is smaller compared to the other stud/terminal. Trace the wire of the negative pole and it will lead to where it is attached to the car body by a nut. Check that the wire is firmly connected to the body, by slightly yanking it left to right. If the wire moves, then it's loose. Clean the connection surfaces and tighten. I personally use a di-electric grease applied on connection surfaces for better contact and surface protection against elements.

Power and electrical troubles are a pain, it's not that easy to diagnose and fix.

Bring it to your dealer, let them fix it.

if you were present during electricity class in school, and you are not afraid of getting dirt and grease on your hands and elbows,
you can try doing what sid says, before you bring it to the fixit shop.
it is always difficult, that first time. but the potential rewards are worth the trouble.