Tuesday, September 13, 2011

Inside an ignition switch–(anoraks only)

Well that title ought to put off most readers, but if you are still with me and have an interest in such things, then read on.

I pulled apart Herbie’s faulty ignition switch to see what was wrong with it.  Don’t do this yourself unless you are replacing the switch because the first thing that happens when you prise off the back is that a few little springs and ball bearings shoot out, and you’ll never get them back in the right place!

If you have a boat with a BMC or Beta etc engine then you may well have a similar switch.  Its a Lucas one but our replacement although identical was made by Durite.


Here’s the back plate

P1050716 (1024x768)

Flip it over and you see this

P1050718 (1024x768)

Note the cam like notches in the centre of the plastic which looks like they might hold the fixed switch positions against the little springs and bearings.  Practically no wear on the contact discs though.


Looking inside the body of the switch we see this


You can just make out the wear on the 3rd and 4th stud contacts.  Not much, but apparently enough to stop the glow plugs from working.  It gives the impression that in some positions, the switch hasn’t been turned far enough.  Do you see what I mean?  It looks like it has only been contacting the edge of the stud.


Anyway, the new switch was easy to get and at £16, not too dear, and fitting it took a couple of minutes.  Herbie’s starting is transformed.


Rick said...

Maybe it's to do with the way the switch operates. All the other switch positions are positive, but in the glow plug position you are just holding the key against spring force from within the switch. This could explain why the edge of the contact is eroded and also why the switch was intermittent - it would depend on the precise angle that the key is turned to operate the glow plugs

Rainman said...

So it's your fault.

Neil Corbett said...

Rick, you echo my own thoughts on this. Does that mean that I now have to attach a protractor to the key ring?

Rick said...

Or fit a relay and give the switch an easy life.

Neil Corbett said...

Then the relay burns out instead of the switch :) One thing about the switch is that it's cheap and easy to get at and replace, as we discovered on Sunday.