Does your ignition light fail to work when switching on? Then check the obvious causes, i.e. burnt out bulb, bad contact between bulb and lamp holder or a bad connection in the wiring circuit. One side of the light is wired to the ignition switch, the other to the dynamo positive wire.

The next most common cause is an open circuit in the wire-wound resistance which is mounted around the outside of the ignition light.

Next question is why have a resistance in the first place? The answer is that the use of it enables a smaller voltage bulb to be used. Usually 3.5 to 4 volts. Using a smaller bulb has two effects. (1) It reduces the voltage in the backflow to the dynamo when switching the light on and (2) the glare from the red light is greatly reduced.

If the resistance is the fault, it can be rewound as original, but it is both troublesome and expensive. The alternatives are: -
    (1)   to completely renew the whole unit or,
    (2)   to consult an electrician who can calculate the resistance value to reduce 6v to 3.5v, then solder this resistance between B and C in place of the original wiring.
    (3) to by-pass the original resistance wiring and use a full voltage lamp consistent with the working system of the vehicle. This solution has been applied successfully with no ill effects except for a very bright warning light - which is impossible to ignore if the dynamo fails. To effect this, first make sure the insulating washer G is in good condition and always replace if in doubt. Then make a connection between B and C, either by joining a short length of insulated wire or by turning the connection washer B around and soldering it directly to C. Fit a 6v, 0.3 amp bicycle lamp bulb. This is about the smallest wattage and does not adversely affect the charging system.

One other problem that may occur is when the engine revs. are just sufficient to put out the ignition light and begin to show charge on the ammeter but with increased engine speed a small sullen glow on the ignition light may still be visible. This is due to either the regulator contact points needing a careful clean, or the spring holding these points losing its strength or finally, it could be caused by brush bounce or a worn or scored commutator in the dynamo. In any case it's nothing to worry about.

Try this simple remedy - so many Sevens have problems in this area and if when judging, an engine running test is required, check to see that all functions correctly.

From an article first published by A70C 1977 with many thanks.