Leading astray

I was doing the final testing following the configuring of Erin Mae's new tachometer, when I ran into another problem – the engine wouldn't stop! You normally stop it with the Stop button, before turning the ignition key back to position zero. Turning the key without stopping the engine first not only doesn't stop it, it also discharges the battery. Fortunately there's a lever on the side of the engine you can use to stop it in an emergency.

I took out the control panel yet again and found that, with all the fiddling around, a wire with a female spade connector was waving at me, having obviously come loose from its connection. But which one! The wire in question was the red half of a chunky 2-core cable which disappeared down towards the engine compartment. The blue half of the cable was attached to two thinner white wires, one of which could be traced to the stop switch, so this was obviously the culprit. But what was the wiring arrangement and where, among the various apparent options, should I re-attach the red core?

The white outer cover of the cable was a bit grubby, but I thought I could make out something written on it. Once it was cleaned I could read, in hand-written orange marker pen, "SUPPLY TO Q2". I knew that to be a breaker switch in the wiring cupboard and, fortunately, I have a PDF of Erin Mae's wiring diagram. That showed Q2 as controlling the horn and the headlight and I'd already noted that a similar chunky cable came up the control panel plinth and was attached in some way to the horn button and headlamp switch. The diagram also showed a straight connection from the ignition switch to Q2 – horn and headlamp are only supposed to operate when the engine is running. A continuity test with my multimeter revealed that the red and blue cores of the cable are joined at the bottom terminal of Q2, which explained things, though it didn't strike me as best wiring practice. The chunky cable is not only taking a 12 volt supply down to Q2 via its red core, but also, via its blue core, taking 12 volts back up again to be used by the Stop switch. Very odd!

The Isuzu marine engine manual shows the back of the ignition switch, and I was able to identify an available terminal which is live when the engine is running, but not needed for engine function. It was obviously a match for the loose wire's connector, so on it went. Nothing exploded or buzzed, the horn now operated again and, crucially, the engine stopped when I pressed the Stop button. Result!

Everything would now have been nearly perfect, but for one thing. The Stop switch has a little red acrylic cover printed with the word "Stop". With all the kerfuffle, it knocked on something, and broke. It's an ex-cover. You can't buy them for 50p, of course. You have to buy a whole new switch for 20 quid.