How do you make the dash charge guage actually read something? Mine only moves the needle so slightly that you are not sure if it works.

 

The guage on my truck does not move that much either. Normally when you put a heavy load on the system, you can see it move at a larger rate. IE: Driving at night in the rain. Lights, Defroster, wipers, etc, all running at once. My trucks guage will bounce around when operating a snow plow. I will also notice it drop considerably when at idle with many accessaries on. It all depends on the current load and how much the alt is putting out. You may want to put a volt meter on the charging system and check how much the alt is putting out. It should show around 14.5 volts when the engine is running. Good luck.

Jakegypsum // Ford fleet, soup to nuts.

 

Yes I have 14.5 volts when running. Seems GM had something about a bad resistor on the back of the guage. Any one hear of this?

 

I run an automotive electrical shop, an have experienced this problem a lot on Ford F-150's. I know this sound's a little too simple, but you probably just have a defective gauge. Verify the charging rate with a test gauge (should be around 13.8 volts)and if OK, you probably need to replace the gauge. Note the gauge reading with the key on and engine not running. It will probably be abnormally low as well.

 

I just noticed that you didn't mention the model of your truck....If it is an 80-86, you probably have an ammeter instead of a voltmeter. This is a completely different problem. Ford's ammeter circuit uses a specially calibrated voltmeter which measures the difference in voltage across a specific length of wire. If your alternator power feed wire has been changed, it will not work correctly. Let me know if this is what you have, and I will send you a diagram of how it should be wired.

 

Yes I have a 1984 F150. Please send the diagram. Thanks.

 

Sorry...Got busy and forgot to get back to you...This may be helpful. Check the main power feed to the alternator to see if it is the original wire. It will have constant 12 volts (key on or off). While it will charge fine if connected directly to the battery, it must be hooked up to the original power circuit for the ammeter to work. A common problem is that a fusible link will blow,(usually at or near the starter solonoid, sometimes taped up in the harness) and the person doing the repair simply runs a new power wire directly from the solonoid. This bypasses the ammeter circuit.

If this is OK, then you need to check the ammeter wiring. The ammeter on these trucks is not like the aftermarket meters which use heavy gauge wiring to route current through the meter. These use two small gauge wires which measure the small difference in voltage at each end of a heavy wire (the factory power feed wire). DO NOT PUT 12 VOLTS ON ONE TERMINAL AND GROUND THE OTHER - YOU WILL DESTROY THE GAUGE. Trace these two wires - they will each connect to a different point on the same wire.

 

You all should search the FTE archives.... I swear I remember seeing a post that told of a procedure that added or deleted a reistor or something and the gauge became a real functioning unit. I really dont know how long ago the post was but I know I read one! Good luck...

Mike
95 F350 Dually

 

Hey guys,

I agree with all the good advice I see in this thread, but, before you start tearing into things too deep, let me tell you of the problem I had and how I almost bought a new gauge.

Last summer I noticed that my volt meter was not showing much charge. As I was about to leave on vacation with the fifth wheel I stopped and had the charging system checked. It was putting out 14.5 volts. So I went on vacation with out getting it repaired. A few days into the trip is was showing even less of a charge... so I stopped and had the charging system checked again... it was okay. Diagnosis: the gauge is shot. Well I planned on replacing it on my return. Since these gauges come in pairs, volts & fuel, and you cannot return electrical components, I thought I'd play it safe, pull the gauges, mark down the part number and go buy the new one.

When I reinstalled the gauges to drive in and buy the part... presto... in was working.

What the problem had been was that the face plate had slipped and was exerting just enough pressure on the center of the needle to restrict movement. This happened again a couple weeks later... so I took things apart again to find a way to stop the plate from slipping. There are some alignment holes in the face plates and in the body of the gauge assembly about 1/8 or 3/16 inch in diameter, top and bottle, they are not visible once all trim panels are installed. I took a McDonald's straw and cut some short pieces about a half inch or so in length. Then I slit each one up the side. I rolled each like a roll pin and inserted one into each alignment hole. I did the whole dash with less than half a straw.

Problem solved... no new gauges.

I can't promise this is your problem, but it's worth checking out... could save a lot of frustration.

Perry