Volvo: Charging System Problem - 1991 240DL, volts and amps, charging system

Question
I am having a problem with the charging system on my ’91 240.  To aid diagnosis of the problem, I put a charger on the battery to make sure it was at full charge.  When the car is started it runs nicely when the battery is a full charge, but after about 10 minutes the alternator light starts to glow and generally continues to glow (sometime brighter, sometime dimmer).  I have to recharge the battery often.

I have tested the current at the battery and the car seems to make 14 volts after I accelerate the engine momentarily.  I do not know if I have a bad alternator or a problem with wiring harness leads to the alternator (a past Volvo that I owned had this problem and exhibited similar symptoms – after replacing the alternator three time I learned the problem was in the harness).

How do I better diagnose the source of my problem, and if I have a problem with the harness leads to the alternator, how do I reroute the wiring to correct the problem?

Thanks in advance for the advice.


Answer
Andy,
First make sure the battery is good have it tested. A bad battery can not accept a charge in some cases. With a good battery test the charging system both volts and amps. Make sure the alt has a ground wire on it. You can inspect the red wires to the alt making sure that they are also in good shape. The small red wire goes to the dash board, you can test that wire for shorting and breakage/fraying. If still in doubt take the alt off and  have it tested. When the alt is out pull out the regulator/brush pack making sure that the brushes are good,(longer then 3/8 of an inch). When the get short they make poor contact, causing low charging. The small red wire to the alt will apply 12 volts to the exciter diode (key on or running) making the system charge. If you are not getting that voltage you may have a bad circuit board in the dash cluster.