I'm guessing my alternator is bad. - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

SixFo Galaxie · 02-26-2005, 10:37

Do any of you have step by step instruction's how to check it out with a multi meter? The batterys voltage is at around 12.30 with the car off and at idle. Shouldn't the voltage go up with then car is running? The little Gen light is also on while the car is driven and at idle. Thanks

Jason

Glen · 02-27-2005, 05:07

Quote:

Originally Posted by SixFo Galaxie

Do any of you have step by step instruction's how to check it out with a multi meter? The batterys voltage is at around 12.30 with the car off and at idle. Shouldn't the voltage go up with then car is running? The little Gen light is also on while the car is driven and at idle. Thanks

Jason

Get a multimeter and set it to DC Voltage, if it has a range set it to 20 volts. start the car and while it is idling you should get at the minimum 13 volts but an alternator in good condition should charge at between 13.8 and 14.2.

One more thing you might want to check is for current draw when the car is off. There are diodes in the alternator which stop the alternator draining the battery when the car is switched off. These sometimes stuff up and create a current draw when the engine is stopped draining your battery. A quick way to check this is get a flat screwdriver while the car is running and just put the blade in front of the pulley (Watch the belts and radiator fan). If the screwdriver magnetises to the pulley get an auto leccy to check it out.

Another way to check if anything is drawing current.

Turn the car off, close doors lights off, key off etc. Get your multimeter set it to amps and switch the positive lead over to amps (It will have 10A above it.) which means it is fused. Take a battery terminal off (preferably postive) and put the meter between the postive terminal and the lead you just removed. If you get anything above .4 you its a worry. Take your car to an auto leccy if the current draw is too high.

Hope this helps.

Glen

ford4v429 · 02-27-2005, 14:39

question- just to clarify, does this car have a generator or alternator? I think 65 was first yr for alternator...

If its a generator, ive read they can need 'polarized' to leave a little residual magnetism in the fields to generate enough current for it to self magnetize when started up. I think they also have brushes/commutator just like a starter motor that can go bad.

If it was an alternator conversion, did it work in the past, or is it a new conversion? if its a conversion, check to see if you are getting voltage on the 'f' (field) terminal relative to ground. 12v here will give max output- if you are not getting field power its more than likely the regulator- the little wirewound resistors underneath often lose connection at the ends from corrosion/heat/etc...I think if diodes are bad, you can remove the belt and try spinning it by hand- ignition on/engine off, if its shorted it will be hard to turn- if it spins freely, you probably dont have any field gurrent or a bad brush/slipring (pull coil wire if still running points so your ignition coil wont pop- ex wife did that to my mustang one day when washing it- had key 'on' instead of 'acc'). good luck

Glen · 03-02-2005, 15:03

Quote:

Originally Posted by ford4v429

question- just to clarify, does this car have a generator or alternator? I think 65 was first yr for alternator...

If its a generator, ive read they can need 'polarized' to leave a little residual magnetism in the fields to generate enough current for it to self magnetize when started up. I think they also have brushes/commutator just like a starter motor that can go bad.

If it was an alternator conversion, did it work in the past, or is it a new conversion? if its a conversion, check to see if you are getting voltage on the 'f' (field) terminal relative to ground. 12v here will give max output- if you are not getting field power its more than likely the regulator- the little wirewound resistors underneath often lose connection at the ends from corrosion/heat/etc...I think if diodes are bad, you can remove the belt and try spinning it by hand- ignition on/engine off, if its shorted it will be hard to turn- if it spins freely, you probably dont have any field gurrent or a bad brush/slipring (pull coil wire if still running points so your ignition coil wont pop- ex wife did that to my mustang one day when washing it- had key 'on' instead of 'acc'). good luck

Oh yeah you might be right about that....I didn't even look at the vehicle he was talkin about..

ford4v429 · 03-02-2005, 17:17

just noticed I mentioned pulling 'coil wire'- should have said 'coil power wire'...pulling the high tension lead off wouldnt prevent toasting it if the points are closed...