Amp Guage

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Nov 18, 2004 | 12:01 PM

Captbo2001

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Amp Guage

I have a 1996 Ford F150 Ex. Cab XLT. When I start my truck and begin to drive down the road, the amp guage on the dash, show it is charging ( the needle is to the right on the + side. By if I have the heater and lights on, and stop the truck for a stop sign, etc. The guage ( the needle goes to the left, as if discharging). You can also notice the headlights go a little dim. But when you begin to excelerate, the needle on the guage goes back to charging. Is this normal ?

Nov 19, 2004 | 07:40 AM

low-side

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Sounds like the batts low or the alt is going out. Needle should move little to none under those conditions.

Nov 19, 2004 | 09:10 AM

jroehl

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Joined: Apr 2004

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From: Lafayette, IN

(psssst...it's a VOLTmeter...ammeters are more expensive than what most car manufacturers would spend on a dash gauge) I agree with the other recommendation, except that I would start with the alternator. An alternator should provide enough power to run your accessories (lights, heater, etc.) at idle, PLUS charge the battery, which was drained slightly when you started your vehicle. Even if you start drawing too much power (like when you jump-start someone else), the idle should adjust to spin up the alternator to produce more power (more rpms = more power, up to the alternator's limits). A fully charged battery should measure about 12-12.5V across the posts when the vehicle is off, and about 13.5-14V when the vehicle is running (that's how you charge a battery--apply more than the voltage of its cells to "backfeed" it).

Jason

Nov 19, 2004 | 11:51 AM

dhag911

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Joined: Jul 2003

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From: Lincoln, Nebraska

mine does the same thing before and after an alternator change i guess i havent changed the batt or even checked then for voltage. i do have higher wattage head lights would that do anything?

Nov 19, 2004 | 11:58 AM

RR4E

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Joined: Oct 2004

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From: Winnipeg, Manitoba

Check for belt slippage/wear, clean your battery posts, check and make sure all your battery cables are in good shape(corrosion on the inside creates resistance) and check the connections on your ignition solenoid as well. One thing people tend to neglect, is giving the battery a nice long(over-night) slow charge with a trickle charger. Before testing your system, try that, and then test it. This will give optimum battery readings, and help narrow down the potential problem. A simple dirty ground connection can cause the alternator to appear weak, most often on trucks this old, there are many rusty ground connections.

Nov 19, 2004 | 02:17 PM

Eric C.

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Joined: Feb 2004

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From: Ocean Park WA

Test it first with a multiemeter and see if what you are seeing is just the **** poor designed stock meter. You may be overloading your alternator at idle if you have headlights, heater/AC, stereo and the plethora of accessories we add now days. It's not unusual for this to happen and unless you spend hours just idling it's not that much of a real problem. All alternators and generators are rated according to rotor speed and if you are below rated speed you will have reduced out put (the problem with under drive pullies). A fully functional charging system will produce approximately 14-14.5 volts dc measured across the battery with the engine running and no accessories. You start adding accessories it will start to drop. Even with just lights you should have at a minimum 13.5 volts. DO NOT REMOVE THE BATTERY WHILE RUNNING. The battery does two jobs in a electrical system, stores and absorbs shocks. An ideally charged battery wil read 13.5 volts with nothing on, 12.25-13.25 volts is a pretty normal charge. If these aren't the readings you're getting test the alternator and I do not remember if your year is the built in regulator or not but if they are the seperate ones and you change one you must change the other.

Nov 19, 2004 | 09:32 PM

pfogle

Lead Driver

Joined: Feb 2003

Posts: 8,140

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From: Oak Harbor, OH

If the blower is on high, it's going to draw close to 40 amps. Most alternators cannot keep up with that at idle, especially if you have the a/c on (or defroster as it cycles the a/c), there are two ways to clear it up. Raise the idle a little bit, or get the alternator rewired to charge full charge at a lower rpm.