Where are the bits that make my Austin FX4 taxi start? What are they doing while I’m sitting patiently turning the key?
These are the questions I found myself thinking after conquering several of the lighting systems of my car in the last few days. It’s a strange order to deal with things – make the lights flash and replace bulbs before making the thing start, but heck, I have to squeeze it in around the day job and family.
I did some basic testing on the ignition key, and lo and behold, it does connect a circuit to the glow plugs if you turn it anticlockwise. From time to time. That’s the fun of owning a 44 year old car. Sometimes things happen in a reliable and predictable fashion – the deterministic universe most of us are used to. And then sometimes, due to the vagaries of Lucas electrical systems, odd lights turn on for new reason and things fail to work.
I’m mentally prepared for this on a good day. My first motorbike – a 250cc Honda Superdream – was like this. I had to push start it every single time for 3 years and 2 engine and countless carb-balancings. The day I came to sell it, it started first time with the ignition in front of the people going to buy it. It’s almost like it wanted to go.
With the ignition out of the dash, things seem to work, so I’m going to reassemble the dash with the plethora of randomly positioned self-tapping screws and see if I get a voltage across the glow plugs again.
It’s delightfully simple – there’s no relay or solenoid. All of the current that needs to go through the glow plugs and the big fat resistor goes from the battery right through the ignition switch. Which is a little harsh in my opinion. Harsh but simple.
The ignition switch is spring loaded when you turn it anticlockwise, and it doesn’t feel like it makes a connection every time – it’s a pretty stiff spring, and a flimsy key – a winning combination if you have a predilection for snapped metal.
[edit] So I think I may have figured two things out. The first is that the key fits in the ignition in two different ways. One is sufficient to allow you to turn the ignition on, but doesn’t let you make a circuit for heating the glow plugs. The lock turns and it seems to be working, but it isn’t. So you have to put the key in the other way around, and then it works. Hurrah. Determinism wins.
The second is that the glow plugs are connected in series… … almost. If the glow plugs are of the correct type, the connectors to the heating element is electrically isolated from the engine (which is now grounded to the negative terminal of the battery). So there needs to be a wire to and from each terminal of each glow plug to complete the circuit. The last glow plug has only one wire going into it, so if it isn’t connected to ground, none of them are going to glow.
So yes! Now with a flick left and then right of the key, then a quick stab of the ignition button, the beast roars into life.