The charging system on MCI coaches has been the same for many years. The only exception is the Renaissance coach. In this
tip, we are going to concentrate on all the models except the Renaissance.
The charging system involves a Delco 50DN alternator and a Delco regulator, with the regulator set to charge at 27.3 volts.
If your coach is not charging, there are a few tests that can be conducted in the Rear Electrical Junction Box to determine
what the failure is.
What tell tales came on when you noticed the coach wasn't charging?
Did just the Not Gen T/T come on or did the Starter Alert T/T come on as well?
If both lights came on, that is a sign that the triple function safety device stopped the charging because of an over-voltage
situation. Double-check the charging rate of the regulator. Reset the triple function device by shutting off the coach, and
turning off the main disconnect switch for a couple of minutes.
If this is a belt driven alternator, is the belt damaged?
With the coach running, check stud 49 in the Rear Jbox. This should read at least 24 volts. This is the power supply to
With the coach running, check stud 48 in the Rear Jbox. This should read between 9-15 volts. This is the power supply coming
from the regulator to energize the Field windings in the alternator. The voltage will depend on the charge state of the batteries.
With the coach running, check stud 33 in the Rear Jbox. This should read 1/2 the charging rate.
If stud 49 reads 24 volts, and stud 48 reads 0 volts, you have a regulator failure.
If stud 49 reads 24 volts, and stud 48 reads 24 volts, you have alternator problems. The regulator is trying to get the
alternator to charge by increasing the Field voltage.
If stud 33 has voltage less than 1/2 the system voltage, then you definitely have alternator trouble.
If stud 49 reads 0 volts, then the alternator and regulator are probably fine, and the Field relay in the upper RH corner
of the Rear Jbox will be the source of the problem.