4840 alternator question

[wec101]

I removed the alternator and had is checked. Auto parts store said it was fine. I may have reversed the two wires when I connected it back. Now the alternator light glow faintly when running and the battery is not charging as I have to recharge it. Seems like it take an awful long time to charge also. Batter is almost new. Any have any thoughts? Could I cause damage if I reverse the wires? thanks

 

[Tazza]

One way i have tested alternators is to have it running then brush +12v across the exciting terminal. Use a beter on the battery to check the voltage before and after. It should run about 12v then after you have excited the alternator, it should jump to about 14.
If you had reversed the power to that terminal, i don't think there would be an issue as rather than 12v it would have had 0.

 

[wec101]

One way i have tested alternators is to have it running then brush +12v across the exciting terminal. Use a beter on the battery to check the voltage before and after. It should run about 12v then after you have excited the alternator, it should jump to about 14.
If you had reversed the power to that terminal, i don't think there would be an issue as rather than 12v it would have had 0.

Thanks for your response---I am not entirely sure I understand everything you said. Please excuse a stupid question but are there three wires to connect tothe alternator or two? I only found two but the on-line manual I found seems to indicate three. Please explain where the wires go to (whether three or two). Thanks gc

 

[Tazza]

Thanks for your response---I am not entirely sure I understand everything you said. Please excuse a stupid question but are there three wires to connect tothe alternator or two? I only found two but the on-line manual I found seems to indicate three. Please explain where the wires go to (whether three or two). Thanks gc

Generally there are only two wires, one heavy one that goes to the battery, this is the one that produces power to charge the battery.
The other wire gets power to energise the rotor to produce power on the fields that feed the heavy wire to the battery.
I have found that all the alternators that i have messed with you can get them producing power by applying +12v to the small terminal on the back of the alternator. After power has been applied while the alternator is rotating, it keeps producing its own power so you don't need to hold the wire on the terminal.
Hopefully some of that makes sense.