Yellow Diamond Electrical Control System
Starter Switches
Description
From the BUT A Series Maintenance Manual:
The starter circuit contains three switches, mounted in the control box.
When the starter button is operated, a solenoid coil is energised in the starter relay, which closes the solenoid circuit of the starter switch. This solenoid draws in a plunger until a bridge piece, mounted on the end of the plunger, engages two fixed contacts, thus completing the circuit between the starter motor and the battery negative terminal.
The starter isolating relay protects the starter motor against inadvertent re-engagement while the engine is running.
It is operated by the output of the engine driven dynamo, which, when reaching a predetermined speed, energises a solenoid coil, this in turn operates contacts to interrupt the starter motor solenoid circuits.
Maintenance
From the BUT A Series Maintenance Manual:
Clean the contacts by wiping them with a rag moistened with petrol. Apart from this the starter relay, starter isolating switch and starter relay switch requires no maintenance.
If any of these switches should prove faulty the matter must be reported immediately.
Schematics
The first schematic is the wiring for the Derby Lighweights with engine mounted dynamos.
For the Derby Lightweights with the underframe mounted dynamos the schematic noted "engine starter relays are modified as shown on Plate 074 and also engine starter switches are deleted." Plate 074 is extracted below.
The second schematic is for the Met-Camm Lightweights.
