11/15/2016 12:09 AM
from MCI website on older MCI Buses with 12 Volt headlights fed by
Click here to go to the Maintenance catalog with wiring schematic.... Look at
section 7, Go to the last page ..
The page before the last one is the schematic to this coach.7
MCI SERVICE INFORMATION
Wiring - 12-Volt Lights on a 24-Volt System
Early MCI coaches used 24 volt bulbs for all the exterior lights,
including the headlamps.
During the mid 1980's the 24 volt headlamps were replaced on the MC-9 coaches
with 12 volt headlamps, beginning at unit 34901.
By wiring the headlights in series, 12-volt lights will operate with a 24-volt
"Not as good "
The problem with wiring lights in series is if one lamp fails, both lamps go
"The Correct Way"
To prevent this from happening, a "balance" wire was added.
This wire is routed from the 12-volt post on the rear battery to the wire
connecting the headlamps
Depending on which headlight fails, the balance wire acts either as a power
supply or ground connection for the remaining lamp.
The balance wire has 12 volts of power on it, which supplies power for the
headlamp connected to battery ground.
For the headlamp with 24 volts attached, the voltage difference between the two
wires will allow 12 volts to flow through the lamp illuminating it (24 volts on
power side - 12 volts on ground side = 12 volts power flowing through light
Service Bulletin #1930 explains
the procedure on converting your older MCI coach over to 12-volt headlamps.
It also lists all the parts required for this rework. Beginning in April of
1992, the exterior lighting on MCI coaches was changed to
operate on a 12-volt system. All coaches from that point on have been using
12-volt exterior lighting, so the above information does
not apply to these later models.
If you need
further assistance, contact the MCI Customer Support Center at (800) 241-2947
From MCI's WEbsite
Factory Electrical Wiring schematic for this Bus
Click here to go to the Maintenance catalog with wiring schematic....
Look at section 7, Go to the last page ..
The page before the last one is the wiring schematic to this coach.7