Troubleshoot Charge Circuit

[Didge]

~~I sold my F100 to my friend this week. I had wired everything myself several years ago. Then the truck sat for a few years and I decided he needed it more than I did.

~~Anyway, my friend gets the truck and starts doing some necessary work to get it road worthy. There was nothing wrong with the electrical system. His step dad sees some wire hanging and decides he knows where it goes. After hooking it up 'wherever it goes' he decides to start the truck and see how its performance has improved since his necessary modificatrion.

~~You all know what happens next. Yes thats right the neighbors all thought they were putting on a barbecue for all the smoke.

~~Now today I went down there and rewired the truck removing the charred remains of all the wiring and hooking everything back up the way it goes. Its all good except the dam thing will not charge. It will be the fault of the regulator, the alternator or both. Eh.. really its the fault of the step dad... But I would like to know if anyone knows how to determine which is at fault, the regulator or the alternetor.

~~BTW, a good explanation of the way the circuit functions might also help.

[Mohillbilly]

If you have a volt meter, check for an output from the alternator of about 14.5 volts. If it is 13 volts or less, the alternator is the culprit. If it is up to par, and you don't get the 14 volts at the battery, then the regulator or the fused link wire is bad.

Good luck,
Steve

[willowbilly3]

Uhm.. the alternator can't charge if the regulator is bad. My first guess would be the reg. but if they let the smoke out of a highly modified system, then who knows. Anyway unplug the connector from the regulaor and put a jumper from across the first and third positions on the wires. (B and A terminals I think) This will full field the alternator to it's maximum output. If the alt. charges with the jumper in place you know the regulator is bad. You will need a voltmeter to make sure but you should be able to hear the alternator charging from it's whine and the pull on the engine. DO NOT rev the engine with the alternator full fielded or you may create even more problems since a healthy alternator is capable of making 18 volts or more.
Also I would suggest you put some circuit protection (fuses or circuit breakers) in the wires that got smoked to prevent the same thing from happening again.

[agricola.versailles]

Just a little trick. Start the car motor and disconnect the positive pole of the battery. If the car motor stop, the alternator is out of service. If the car motor remains running then the regulator could be malfunctioning. Put a Volt teste between both poles of the battery and you should have between 13 and 14 Volts dc in the tester. If all is correct then the battery is dead.

[willowbilly3]

Uhm.. we used to do that all the time but it is a good way to destroy lots of electrical components. With the battery cable disconected there is no battery to buffer any voltage spikes and if you rev the engine with it disconnected it will very likely blow out any light bulbs and cause other damage.

[agricola.versailles]

Yes willoby you are right. I forget to explain that this trick could be done just with the engine running. No radio, lights, ... The regulator has some diodes that protect him to shorts...of course the best way is to call a technician to check it.

[willowbilly3]

Many of us have done that with no problems, I just do not like to recommend to others since it is easy to damage the system.
My old Fluke 77 goes everywhere with me. Quite often it is the only tool I have. A quick look at the volts in a system tells a lot.