| Diagram | Fig. 25 — Basic Electrical Components — GROUP 25 · ref 21 |
| Listed in parts books | 1971–1973 |
Switch, Master
Lucas master (ignition/lighting) switch, PN 39784, appearing in catalog entries from 1971 to 1973.
This is a Lucas master switch, listed in the shop's electrical group as the basic ignition/lighting switch for the bike. It's the multi-position switch that controls power to the ignition and lighting circuits from the key or lever position, and it's the kind of part that tends to get gummy or corroded with age since it lives out in the weather on the headlamp shell or nacelle.
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Our catalog record shows it appearing across entries from 1971 to 1973, and it turns up under a few different part numbers in other references, which is common with Lucas switches that got carried across model years with minor number changes.
If you're chasing electrical gremlins - a bike that won't fire, or lights that cut out - this switch is a common suspect. Confirm the exact switch body and connector arrangement against what's on your bike before ordering, since Lucas used a few different switch types through this era.
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