Alternator, 2007ford Ranger, 4.0 v-6 engine.

MIKE RUPY

MEMBER
2007 FORD RANGER
6 CYL
4WD
MANUAL
72,500 MILES

Bad alternator. Dealer says they removed and replaced defective alternator. When engine was started, they claim new alternator went bad. After days of trouble shooting their determination is there is a wiring problem. Termination plug at the alternator consists of three wires. The first wire is a purple wire that terminates at another termination plug which is plugged into the alternator. The second wire is a red wire that terminates I am not sure where. The third wire is a grey wire that terminates, or originates, I'm not sure where; starter solenoid perhaps? I do read a ground on the grey wire when checked at the termination plug. My primary question is: if I install the new alternator, will it go bad. Ford does not seem to want to answer any of the questions I pose to them with respect to the circuitry that this system is comprised of. Furthermore, would you venture to guess where the grey wire originates from or terminates at. I'm certain, almost certain, the alternator is grounded to the engine block. Battery light is on.

4 Replies

CARADIODOC

MECHANIC
33,741 POSTS

The only thing on the truck that can destroy a generator is the output wire shorted to ground and the fuse blown.

Your wire colors have changed from what I'm familiar with but we can identify them by their voltages. The fat output wire must have full battery voltage all the time. One small wire must also have full battery voltage all the time. If it's missing, look for a blown fuse, typically a 15 amp. Another small wire should have about 2.0 volts with the ignition switch on. That circuit is working because the battery light is on. The last wire comes out of the generator and is plugged into it again. That one will have around 6.0 volts when the system is working, otherwise it will have 0 volts.

Start with those measurements and holler back with your findings.

Caradiodoc

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Monday, February 7th, 2011 AT 7:56 PM

MIKE RUPY

MEMBER
3 POSTS

Did everything you suggested. Checked voltages. They all read just as you indicated. Found no blown fuses. Installed new alternator. Battery light still on. Voltage at battery is 12.5 volts with engine running. Not quite sure what to do now. Defective alternator?

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Tuesday, February 8th, 2011 AT 3:17 PM

CARADIODOC

MECHANIC
33,741 POSTS

This photo shows the common voltage regulator built onto the back of the generator. See that screw that says "Ground here to test"? Use a jumper wire to ground it while the engine is running. Measure battery voltage at the same time. It should go higher, well over 15 volts if you let it. Remove the jumper as soon as you see what happens. Don't drag the test out any longer than necessary.

If the voltage goes up, the voltage regulator is defective because that's what you just bypassed in that test. If voltage doesn't go up, measure the voltages on those two screws and holler back.

Caradiodoc

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Tuesday, February 8th, 2011 AT 7:34 PM

MIKE RUPY

MEMBER
3 POSTS

Thanks for your help. Actually, I had to fall back to your original trouble shooting procedure. One of the 12 volt wires, the smaller of the two, was broken in half. I spliced the wire back together, that cleared the problem. Charging system working correctly. Thanks again.

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Friday, February 18th, 2011 AT 1:01 PM