Battery light on

[kariwyrick5]

I have a 2005 Ford focus ses zx4 2.0 automatic transmission with ac and Calif omissions. I have got a new battery, alternator and serpentine belt. Battery light still on goes on and off???? Help. I am a 54 year old disabled woman on SSI not wanting pitty just sound advice

 

[Handy Andy]

The "Battery Light Still Goes On and Off" is the one that has me confused here.

The little Battery symbol is for the charging system.

It's either on or off, but if it's blinking - then the system is telling you a type of condition - so it will set a code - and you should also see your check engine light on too. Not just the Battery icon, the Engine icon would be on too.

Now if you are having idling problems - then the condition becomes more serious for if the engine is acting up - either because of the electrical fault, caused by a short or loose wiring or the engines unsteady operation is causing this - because the engines own speed drops too low to maintain the alternators' ability to spin and generate power for the ignition system - I can see where that little battery symbol would go on or off.

So, if you can start the car, and have replaced the battery, alternator and the belt - then the problems left are with the wiring.

Requires a tester and several tools - a multimeter with test probes and the tester to check the load - or ability of the charging system to put a charge into the battery and maintain the engines own ignition power to keep the system running.

This is not an easy thing to do for anyone - so it will need a trip to the shop for them to locate the wiring that can cause this fault.

You have a 2005 Focus, so brace yourself, for it may have a considerable cost in diagnosis and repair - for they will have to run diagnostics which is simple enough, but to track down the problem is what can cost the most in labor. As for checking the wiring is labor intensive and to have a mechanic do this is costly in having to pay them for their time to locate the fault.

This type of repair requires verifying the voltages present from the alternator are correct and that the wiring to the battery and the rest of the system is functioning as it should.

The Alternator can be fine, but if the output of the alternator can't make it back into the battery - you'll have a dead car soon enough.

Same can be said for the system itself - it uses the vehicles processor to help monitor the charging system and show that icon on your dashboard - and it (Processor) also sends/stores information - requires an OBDII scanner tool to see it, this information is so the alternator knows how much power in both voltage and current to keep the system running - a process called regulation.

So, the Ford Alternator uses a wiring harness to talk to the car and the car then talks to it to say I need this much power.

Now, this is a simplified diagram, and it's for a typical later year model vehicles' charging system - but what I want you to pay attention to is the wiring and color code - so the wires from your cars alternator can be found and identified - so you can even inspect this yourself.



How this Regulation works is.
The battery puts out power.
The system sees and compares the power level to a known reference.
The system tells the alternator to either boost or reduce the DARK RED wires output by changing the power present on the Red Blue and Grey wires, this changes the power present on the Alternators Output terminal - the Dark Red wire.

The Dashboard (Instrument Cluster) uses a lamp labeled "Charge Indicator" that lights up when things with the charging system are wrong - that lamp shows up as your Battery Icon you see.

The reason this could get expensive?

Several of them are...

• Corroded wiring
• Loose connections
• Poor / rusted terminals
• Poorly done repairs
• Hidden impacts

The last two are the ones I'm concerned with, for if you have had work done to the vehicle and it was not properly dressed in the loom or poorly sealed from the elements - the wires then can break (or short) and quit working. A hidden impact or other work done in the engine compartment not properly replaced can do this.

The Alternator can and will still produce power even if the other wires aren't present but provides no regulation of it - so the main output post is working - else you'd be here complaining of a dead battery and the alternator is bad - a mechanic can fix that problem.

The poorly done repair can be from many things - up to and including when they put the new alternator in. IF they did not check the old one for wiring problems - as in; why did it go bad? Then, Unfortunately, in their haste to replace - the new one just fried itself. Now you have two dead alternators and still have the condition that caused it, undiagnosed and not fixed, it has to be repaired first - then a new alternator can be installed, and you will be on your way.