Tuesday 18 October 2016

Circuit diagrams

I've always loved circuit diagrams. As a teenager I used to draw out circuits for radios, both valve and transistor, and other electronic stuff. It almost mattered more to have a perfectly balanced diagram than to actually make the item thus represented. All part of the fascination with patterns. So I was delighted when Erin Mae came with a set of wiring diagrams, and that the manuals for the Isuzu 42 engine also showed how it was all connected. Not that I was expecting or hoping to do anything with them – but I like to know.

When the tachometer (rev counter) and the warning buzzer failed a few weeks ago I pored over these diagrams to see whether there was any indication that the two could be linked. Events since have only added more layers to the question. Replacing the ignition switch seemed to resolve some of the issues with warning lights, but I can't see why it should have done if the engine itself was starting and functioning normally.

I 've realised that the whole thing is complicated by having had a battery charging control device fitted three years ago. I'm very pleased with how it works, but I know that installation entailed moving some of the alternator wiring around, and I haven't yet looked down the hole and traced exactly where some of the connections run. So I'm currently not quite sure of the relationship between the diagrams and the reality.

I've bitten the bullet and ordered a new tachometer – an updated version for considerably less than I was being quoted for the original. When I come to fit it I may just find that giving the wiring a good old rattle as I do so sorts the buzzer out once and for all!


  1. My tacho works of but after a few years when the engine hours counter died in the winter and returned to life in the spring it has finally gone AWOL for good. I think I will live with it but like you I would replace a failed tacho

    1. My engine hours counter was dodgy almost from when we acquired Erin Mae. I think it may have continued counting – just that no numbers were visible on the screen. Every engineer I spoke with said that was normal!