Aircraft style ignition switch problem (switch OK but can't turn engine off)

[Drumster]

Normal starting procedure for me is:

1. Battery master switch key on

2. Flip up ignition switch

3. Wave immobiliser fob over immobiliser aerial

4. Press red starter button

This all works fine.  I then flip the ignition switch down and it should turn off the engine but it isn't so I have to resort to turning off the battery master switch.

Any ideas where to start? I was thinking that the switch had gone U/S....

[sjl1]

This happened to me recently after switching lights, fan, wipers, screen all in at same time, welded ignition relay contacts closed so ignition wouldn't deactivate. Try replacing ignition relay with one if the others to test. Relays are only a few pounds so worth carrying a spare

[Nigel Fox]

Hi Chris,

I've had a number of failures of toggle switches used for the ignition. I've just fitted a new 40 amp one from demon tweeks.

i once fitted a fan override switch which I later discovered back fed the ignition switch, couldn't stop the engine when fan override was activated. Needed a minor circuit redesign. Have you fitted any accessories?

Mine car is of an age that doesn't have a relay in the ignition circuits, I'm not sure about yours but it must be a similar age.

[Nigel Fox]

I should add that faulty toggle switches usually have a change in feel when operated. A meter across the switch terminals will soon tell you.

[Drumster]

Sjl1 - Thanks, but my 7 is similar vintage to Nigel's and hence no relay for the ignition. I do though carry spare relays.

Hi Nigel, interesting to note you have had various failures. Mine is/was the Longacre 40 amp one from DT fitted way back in 2008. I'll dig the multi-meter out tomorrow and check, hopefully it's as simple as that (but switch doesn't feel any different to me)

[anthonym]

i'm having an occasional same issue with my ignition key (turn key push button), when key off doesn't work.

[Wrightpayne]

I had a standard ign switch fail (British Leyland type). They have a series of small springs inside which exert pressure on a copper plate that makes the circuits. In mine one of springs broke so wasnt bridging the contacts correctly. I managed to source a land rover switch from Rimmer Bros, which, with a bit of fettling, fitted in my original ign barrel. I posted about the fix on blatchat.

Ian

[Drumster]

Hmmm, switch is OK but I've tested again with another similar switch and still the same result. Thinking it might be the immobiliser I bypassed that and still the same result, engine won't turn off. With immobiliser out of the equation the engine now wouldn't turn off  via the BMS either so I had to stall the car at which point wisps of smoke were coming from the resistor on the BMS!

Just back from 1,100 mile trip to France where everything worked ok. Only change since coming home is to take the scuttle off to remove the mechanical type VDO speedo for repair. Could I have dislodged a wire and if so what would cause this problem?

[Paul Deslandes]

Don't know the vintage/build spec of your car but it sounds as though the alternator is continuing to power the electrics after switching off the ignition.  From your last post I'd start with looking at the cut out switch connections.  As you referred to the resistor you must have the FIA type switch which should both disconnect the battery and ignition, and dump the resistor across the alternator.  Sounds like a short around there somewhere.

Good luck

Paul
 

[Drumster]

Hi Paul, I have a spare FIA BMS and have tried that and still getting the same problems.

The car is 93 vintage that itself has no bearing on this problem as it has been running a 2.0 Zetec with a K6 Emarald since 2012. I'm still only able to  the engine off via BMS.

Another point to note, is that with BMS switched on ignition can be turned on and off via the ignition switch as long as I don't actually start the engine, it just won't turn the engine off once it is running.

Trouble is I've reached my level of electrickery in cars... (probably obvious already)

[Paul Deslandes]

Certainly sounds as though the alternator is powering the electrics, even with the ignition off.

Very difficult to diagnose a fault like this remotely but when you refitted the scuttle could you have trapped a wire, although I would have expected smoke rather than your problem!

If you're anywhere near Guildford I'd be happy to help.

Paul
 

[Drumster]

Paul, I'm not a million miles away but not exactly local I'm over in Heathfield, East Sussex. Happy to travel. Perhaps we can speak? 0779three 56135eight

[Nigel Fox]

Chris,

With the engine not running, take the wires off the switch and check the voltage to earth. Obviously one side comes from the battery, is there something live on the other terminal. There could be a back feed from an unswitched live supply.

[Drumster]

Nigel,

Just tried that and one wire is live the other isn't...

[Nigel Fox]

Well that might support theory of an alternator fault. How about connecting the meter to the non live side of the switch, start it up and see if you have volts there when you switch off.

[Paul Deslandes]

If you don't get to the bottom of it then you'd be very welcome to come over to Gomshall (A25 between Dorking and Guildford).  I'm retired so around most days during the week if that's any help to you.

Paul

[Drumster]

Hi Nigel,

That all worked as it should.

However, earlier in the evening someone got me to check the resistance on the alternator leads and the little spring clip that holds the alternator plug in place wasn't secured and the plug was loose, possibly creating a poor connection? Anyway plug and spring were firmly secured and when carrying out your last test (first time car has been started since before the alternator plug issue) everything worked well.

Could it really have been as simple as a loose alternator plug?

(feeling rather stupid now   )

If the issue has been resolved then thanks to all who have tried to resolve my little problem 

[Nigel Fox]

That's great if alls well, I expect somebody can explain it but I'm not sure I can!

[Paul Deslandes]

I can't quite see the mechanism but on older cars the alternator connector links the battery to the fuse box and also has a separate connection to the battery as the voltage sense for the regulator. I can only think that one of these not being made correctly caused the problem. Anyway, really glad to hear that it's fixed.

Paul

[Jonathan Kay]

Could it really have been as simple as a loose alternator plug?

Looking forward to hearing if that's solved it.

Same thought as Paul's: What sort of alternator, and how many terminals and thin wire connections does it have?

Jonathan

[Drumster]

As the car is a '93 x/flow that has had a Zetec transplanted into it, the wiring remains the same as does the type of alternator which is a Valeo. The main plud has 3 spade connectors and the 3 wires according to the wiring diagram go to battery -ve, ignition warning light and fuse box.

Everything is still working tonight, but have to say I'm not entirely convinced by my explanation above as I'm using original ignition switch and BMS and tonight I unplugged to alternator plug and yes the engine still stopped as it should, so unsure how a poor connection might affect this.....

Maybe something shorting in the loom or near the switch? When I put it all back together I'll carefully look for anything unusual. Maybe the switch is temperamental, so I've ordered a new switch to fit anyway.

 

 

[Jonathan Kay]

The main plud has 3 spade connectors and the 3 wires according to the wiring diagram go to battery -ve, ignition warning light and fuse box.

Is that a thin wire to battery -ve from a small terminal as well as the fat charging wire?

Jonathan