Ignition/Headlight Fault Query

[soboleaj]

I have a 2014 (Duratch) Supersport R and a fault has arisen whereby the engine won’t turn off when the headlight switch is in position 2 (dipped and/or main beam position). 

This is because the ignition is now being switched on by the headlight circuit as well as the ignition keys......... Has anyone had the same problem?

 

[ChrisC]

Has it just started doing that, or have you just noticed it’s doing it?   A guess would be a wire going to the wrong connection (fuse or relay box maybe) more than a broken wire or worn insulation etc.  

[Jonathan Kay]

Haven't heard of that. Any recent work?

Do you have a wiring diagram and a multimeter?

What sort of light and ignition switches do you have? And do you have a battery master switch?

Jonathan

[ChrisC]

Good point the push button switches have a controller / relay board

https://caterhamparts.co.uk/other/3751-instrumentation-circuit-board-r500-seven-485-duratec.html

I always wondered if that's a RS232 connector, so is it programmable.  

[soboleaj]

Just started doing it, so was obviously wired up correctly in the first instance

[soboleaj]

Hi Johnathan, the wiring diagram is just about illegible, but I do have a multimeter. They are rocker switches and I don’t have a battery master switch. 

[Jonathan Kay]

If you'd like a better diagram please send me a Private Message with your email address and details of the Seven.

...

I definitely don't have a pat explanation.

* Experts, please: could this be a version of a poorly earthed lamp driving another circuit, in this case the ignition?

...

Here's what I'd do first:

1. Check that all lamps are coming on fully bright, easiest in the dark.
2. Get the light switch out and check that the connections are appropriate to the diagram and well-made. Disconnect the feed to the switch and confirm that the problem then disappears regardless of switch position.
3. With the light switch connected pull each of the lighting fuses one by one and see if the problem disappears.

Jonathan

[revilla]

OK I can only really help if the wiring is similar to a K Series, but ...

Certainly on my car, looking at the wiring diagram, the lighting circuit is pretty much completely independent of the ignition switch and there is no ignition-switched positive feed anywhere in the lighting circuit. So I don't think a poor earth in the lighting circuit could then result in a feed back out onto the ignition switched circuits.

So you're looking for somewhere where the two do come into contact, something which has wires from both the lighting circuit and and ignition switched positive wiring. The only obvious place is the dash instrumentation, particularly the tachometer. A short inside there could cause this as it has a feed from the side light circuit for illumination and ignition switched positive.

On yours there may be other instruments with similar feeds. The good thing is that all of the instrumentation feeds are fused, so you can quickly eliminate this path by pulling fuses. If you can find the fuse which feeds the dash instrumentation illumination (on the K Series its Fuse 6, described as RHS TAIL LIGHT), pull that out (confirm that the instruments no longer illuminate) then see if the problem goes away, this will narrow it down to this area or not.

If this does fix it, you're left with tracking down where the problem lies within the instrumentation. If it was my car I'd go straight for the tachometer and try unplugging that, but on later cars the instrumentation circuitry is a lot more complicated. I think the tacho acts as a central control for other instruments so as a first point of call I'd still go for that next.

[Nigel Riches]

Had a similar problem occasionally on my 1987 XR2, so years ago, turned out to be a hanging headlight relay not disconnecting when switching the lighting circuit off, didn't investigate very closely, but a whack with a mallet whilst it ran on stopped the motor, new relay, no more problem, so if Henry's car company can do this I'm sure Caterham could do it, good luck with this type of fault, usually tricky to track down.

Nigel