Fuses blowing instantly...PLEASE help...

[bb]

I have a 2000 Ford Ranger that I am attempting to repair for a friends teenage son. The main symptom is that Fuse #2 and #26 blow as soon as or shortly after the vehicle is started and the airbag light on the dash lights up and remains steady. Also, both headlights blew within 10 seconds of turning them on. I checked the voltage in the headlight socket and it reads 15.4v. This is the same reading I get at the battery with the truck running. Is this too high? I know my way around a vehicle fairly well mechanically, but unfortunatley, my electrical knowledge in minimal. I have a meter and can check the voltage on a connection, but that is about where my electriacl skills end. The battery is going bad and the truck has had to be jumped several times while troubleshooting. Could a bad battery cause these problems? Any help would be greatly appreciated. He doesnt have alot of extra cash for costly repairs, and I'm trying to help out however I can. I've spent countless hours reading Ranger message forums, but cant seem to locate a solution. I'm very thankful that forums such as this one exist, and hopefully someone can lead me in the right direction.

Thank You,
Brian

 

[wanebell]

Brian,

First off, welcome to TRS!

Now then, a fuse is used to limit the amount of electrical CURRENT that flows through a circuit. It does this by using a small diameter conductor that will melt if the current flow through the conductor is higher than the fuse rating. Voltage on the circuit really doesn't have much effect.

When a fuse blows out as soon as the circuit is energized, this is almost always an indication that the circuit is shorted to ground. The most common cause is a wire that has had the insulation rubbed off, allowing the conductor inside to make contact with the frame or other grounded metal. These problems can be difficult to find and correct. The best way to go about this is to disconnect everything from the load side of the fuse and then reconnect everything one item at a time until the fuse blows. The last item that was connected is the source of the problem. This method will require you to have a good circuit diagram so that you can locate the connectors and wires for each circuit. The electrical schematics located here on TRS in the technical library may be of some limited help. You may also be able to get some help from a Chilton's manual that can be checked out from your local library.

Another way to go about it is to check your owner's manual to see what components are powered by those fuses and check the wires going to those components for bad spots in the wiring.

Either method will be a very painful and tedious proceedure.


As for the battery, no, a dying battery will not cause these problems. However, these problems may well be why the battery is dying. If the shorts are causing a current drain while the motor is off, they will most certainly cause your battery to die.


Oh, one last thing: 15.4 volts with the motor running is not too high a voltage. 16.5 or higher would be a cause for concern.

 

[MAKG]

15.4V would have me a bit concerned. I'd be much more concerned if it varied with RPM (above about 2000). That indicates a failed voltage regulator (integral with the alternator on most RBVs). I strongly suggest this has happened, due to the blown headlights (unless they are halogen bulbs and you touched them...oops).

The charging system should be putting out around 14V at 2000 RPM.

 

[RangerFella]

I'm with MAKG, bad voltage regulator. Try turning on the wipers and then revving the engine up. If they start moving faster with higher RPM then you've definitely got a bad regulator.