Brake light switch

[Rascall]

Had an intermittent fault on the front brake light, disconnected the loom feed to the switch and measured voltage at the loom connectors - 12.6V, Tested the resistance of the switch and it appeared to be switching on and off - ok, reconnect everything and no brake light. Turn of Ignition push probes into switch/loom connectors and tested the switch again all was fine. turn on Ignition and measure 12 .6V again on loom connectors. Starting to think I was going mad. Disconnected switch again and short connectors on loom and the brake light comes on and off no problem. The switch was working if tested on the AVO but obviously not under load.

Fitted a new switch (thanks Moto Rapido) and all is ok but i'm still mystified how it tested ok on a meter but not in circuit.

Russell

[Dukedesmo]

Is the switch actually switching?

I ask because there is a small cylindrical shaped spacer that actuates the switch from the lever (on some models) and these can get lost. Although if the new one is OK then it must be right but it could be an actuation problem rather than electrical...

[AndyC_772]

What resistance did you measure when the switch was closed?

[Rascall]

The switch was switching, swinging between 1.5MOhm and 0.8 ohms depending on position (both on the lever and hanging loose). I thought I was going mad. I can only assume that the wire must be close to broken and the small current passed by the tester was ok, but as soon as the bulb was in circuit the current passable was inadequate to light the bulb. Im no dummy with electrickery, I design and build valve amplifiers and power supplies as a hobby. I was questioning my sanity


All sorted now

Russell