All early Motoplat ignition systems share the same basic features and
operational characteristics. The most critical electronics are contained
in the external ignition secondary coil, the lighting/ignition primary coils
are contained in the stator assembly. There are 2 basic Motoplat units
found on vintage motorcycles, external rotor (flywheel) and internal
rotor. The flywheel type, with lighting coils is the most common.
It is found on many MX and Enduro bikes. The internal rotor type has no
lighting coils and is found mostly on competition MX bikes. There are
several variations of the flywheel type. The information below will deal with them. I will list and
describe the most common ones:
#1. I believe this is the earliest type commonly found. It has a
replaceable diode in the stator. It is identified by a diode symbol (an
arrow head pointing to the top of a T) on the front face and a large notch on
the outer circumference (containing the diode) near the position where the
wires come out. The wires going to the ignition coil have clear
insulating covers.
6 volt lighting coils
Yellow wire, 35 watts {head light}
Green wire, 18 watts {stop light}
Red wire, 5 watts {tail light}
Black wire, trigger circuit to ignition coil small terminal
Blue wire, capacitor charge wire to ignition coil large terminal and kill
switch
#2. Similar in appearance to #1 but no notch, although it still has a
diode in the stator. The wires going to the ignition coil have clear
insulating covers. The wire colors and wattage values are slightly
different.
Yellow, 35 w {head light}
Green, 21 w {stop light}
White 5 w {tail light}
Black, trigger {small terminal}
Blue, capacitor charge {large terminal} and kill switch
#3. Similar to #1, however there are some important differences. It has no diode in the stator (it is has
been relocated to the ignition coil), there is no notch, and no diode symbol on
the face of the stator. The easiest way to identify it is by the red
insulators on the wires that go to the coil.
Yellow, 35 w {head light}
Green, 21 w {stop light}
White, 5 w {tail light}
Black, trigger {small terminal}
Blue, capacitor charge {large terminal} and kill switch
There are 2 types of ignition coils for Motoplat, as
follows:
Black spark plug lead. This type has no diode in the coil.
Red spark plug lead. This type has a diode in the coil.
The black
wire coil can only be used with the early (#1 & #2) stators with the diode. The red wire coil can be used with all three types of
stators.
#3. Testing the
stator WITH diode (#1 & #2, clear insulators and diode symbol)
Disconnect the black wire from the ignition coil. Disconnect the blue
wire from the ignition coil and the kill switch. Connect one lead of the
ohmmeter to ground. Connect the other lead to the blue wire. Note the reading. Interchange the test
leads and note the second reading. In one connection the reading should
be infinity, in the other, 3,000 to 9,000 ohms should be indicated. If a
reading of very low resistance (0 to 50 ohms) is obtained in both cases, then
the diode is defective. If a reading of very high (over 15,000 ohms to
infinity) resistance is measured, there is an interruption in the stator plate.
#4. Testing the stator WITHOUT diode (#3, no diode symbol, red insulators in
coil leads)
Disconnect the black wire from the ignition coil. Disconnect the blue
wire from the ignition coil and kill switch. Ground one test lead from
the ohmmeter. Connect the other lead to the blue wire. A resistance reading between 140 and
180 ohms indicates the charging coil is in order. Next connect one test
lead to the black wire and the other lead to the blue wire. A resistance
between 16 and 24 ohms indicates the trigger coil is good. A low reading
(less than 15 ohms) indicates there is a short in the trigger coil.
Whenever an electrical problem is encountered, always check all terminals and connections to ensure they are clean and tight. If the
problem persists or reoccurs, you should THOROUGHLY inspect all wires, terminals, and connections. You should disconnect, inspect and
clean every junction. Check each wire for kinks, nicks, and abrasions. It is also a good idea to check each wire with an ohmmeter to be
sure it is not acting as a resistor. Its also very important to ensure all components are properly and thoroughly grounded. Again remove
each component, inspect and clean, before reinstalling it. Most problems can be traced to a poor connection or faulty wire.
