S W speedo

[Paultrehberg]

How/what controls the magnet on the side of this speedometer.?

[Chris Haynes]

You have a Police speedometer. The magnet is the needle lock. A button on the handlebar engages it. Another button on the side of the dash cover releases it.

[MMasa]

Like Chris said, that is the speedometer hand lock SOLENOID. It's a coil of fine copper wire wrapped around a tubular center/core. When a button is pushed on the handlebars, current flows through the coil, magnetizing it and pulling the spring loaded end plate down (which is attached to the plunger inside the hollow core). The plate gets latched in the energized position by the spring loaded clip on the plate end. Meanwhile, the rubber tip of the plunger is being held firmly against the speedometer needle wheel inside of the speed effectively locking it in its position the moment that the button was pushed. A purely mechanical button protruding from the left side of the dash cover acts on the plate latch and releases it from its locked position and freeing the needle as well.
Mark

[exeric]

Was that S-W solenoid 'tattle tale' available to the public? Seems like it was a popular feature on Corbin speedos.

[Paultrehberg]

Thanks . What kind of button on the handle bars (right/left side?) would have been used to energize the coil?

[MMasa]

Same as the horn button but on the opposite end of the handlebars.

[Rubone]

The coil was energized by a contact terminal on the dash. The button grounded it and completed the circuit. They came in 6V and 12V versions.

The pursuit light switch is also mounted on the right side

[steuerm]

When the speedometer trip wire/sheathing exited the handlebars was it routed on the right side of the neck or was it routed on the left side through the clamp on its way to the Speedo?