Engine keeps running with ignition off!

Andries

Andries

Member
Hi Guys,

Major electrical foibles have landed! Car in question is a '69 3500S.

When I have power on the car (battery earth cable connected) the ignition- and oil warning lights come on, fuel level indicator rises like it would when you switch the ignition on. Electric fuel pump has a seperate switch but the switch is powered so in theory in would be powered as well. When I start the engine the warning lights go out and everything is normal. Alternator charges (says the ammeter). When I want to turn the car off with the ignition key the engine keeps running....

Which implies that I have 12 volts at the coil all the time! Either through the starter solenoid bypassing the ballast resistor wire or through the tacho and through the ballast resisted wire! Tachometer doesn't work as well (but this could have another reason due to electronic igntion being fitted to the car).

Equipment -

- ACR altenator with a bypass of the Lucas 4TR and 3AW ignition relay. 3AW bypassed brown/yellow to brown/black. 4TR bypass in strange, how should it be done? Altenator has 3 wires going in (or out).
- Electronic ignition (Lumenition) with the tacho on the negative side and the non-ballasted wire from the solenoid on the positive side (?)).
- Measuring 12V at coil between negative side of the coil and an earh.
- Recently changed the fusebox with another original fusebox (wires checked, checked and checked, its ok).
- Recently changed ignitionswitch/barrel/steering column lock for a NOS NADA one, old owners laziness to hand over extra keys and general flopiness of the keybarrel after 43 years.

Really puzzled :roll: ! Any help would be appreciated.
Kind regards,
Andries
 
Andries said:
- Recently changed ignitionswitch/barrel/steering
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Sounds like that might have something to do with it Andries. Was everything ok before you changed the ignition switch? Could you inadvertently cross-connected some wires onto the switch?

Dave
 
Dave3066 said:
Sounds like that might have something to do with it Andries. Was everything ok before you changed the ignition switch? Could you inadvertently cross-connected some wires onto the switch?

Dave
Click to expand...

It was the same before I changed it but I didn't really bother because there was rust-protection marathon going on! The wires are connected in the same way as before and cross checked with the workshop manual..
 
In that case have you physically measured to see if this is in fact the case?

Andries said:
Which implies that I have 12 volts at the coil all the time!
Click to expand...

If you do find a permanent 12V at the coil trace that wire back to source, physically, not by using the wiring diagram, and see where that 12V is coming from. If the wire disappears into a loom it may be easier to disconnect the wires at the ignition switch one by one while you look to see what happens to the coil supply.

Dave
 
Dave3066 said:
If you do find a permanent 12V at the coil trace that wire back to source, physically, not by using the wiring diagram, and see where that 12V is coming from. If the wire disappears into a loom it may be easier to disconnect the wires at the ignition switch one by one while you look to see what happens to the coil supply.

Dave
Click to expand...

Hi Dave,

Permanently 12V on the negative side of the coil. On the negative side of the coil are two wires on the same (double Lucar) connector. Brown (non orginal) should go to the starter solenoid and purple which goes to a control box of the electronic ignition (very silent humming sound when both are connected). The brown wire should go to starter solenoid because on the positive side there's a wire which runs to the tacho (traced) and another one to again, the electronic ignition control box. I do wonder why the ballast-bypass wire from the solenoid and the wire from the tacho are on the negative and positive side? One should rule the other out (ie. the ballast bypass wire should give 12V when starting the car and the ballasted wire should work under operation at a lower voltage).

Thank you for your reply,
Andries
 
The negative side of the coil should be going to the distributor on a negative earth car. All of the supplies (the ignition supply and the direct supply from the starter motor) should be on the positive side.
 
harveyp6 said:
The negative side of the coil should be going to the distributor on a negative earth car. All of the supplies (the ignition supply and the direct supply from the starter motor) should be on the positive side.
Click to expand...

Thanks for extra reference Harvey, you are truly a P6 encyclopedia!

7,3 volt on the negative and 16,2 on the postive side. I'm getting rather sick of this foible.. The fusebox and ignition switch are ruled out of the problem, next suspects are starter-relay and wiring, lpg relay, electronic ignition and really anything non-Rover installed crap!
 
Andries, you need a diode in the secondary wire from the alternator to the little red light. What's possibly happening is that the alternator is charging as it should be, keeping itself energised by effectively bypassing the ignition lamp and switch, by allowing 12V back up the control wire onto the 'off' side of the switch.

It's exactly the problem I had with the midget after the engine swap, and is quite disconcerting! I added an N001 (maybe!?) diode in the smaller of the two alternator wires to stop the alternator feeding the switch from the wrong side, since that there is no more problem.

The alt can manage with 2 wires, 2 of the connectors on the 3 block thing on the body of the alt are joined together anyway. Sounds like the diode has been missed out when the conversion has been done; some alts have this particular diode in the rectifier pack, though the K-series one didn't!
 
1396midget said:
Andries, you need a diode in the secondary wire from the alternator to the little red light. What's possibly happening is that the alternator is charging as it should be, keeping itself energised by effectively bypassing the ignition lamp and switch, by allowing 12V back up the control wire onto the 'off' side of the switch.

That would explain the excess voltage !
Click to expand...
 
1396midget said:
Andries, you need a diode in the secondary wire from the alternator to the little red light. What's possibly happening is that the alternator is charging as it should be, keeping itself energised by effectively bypassing the ignition lamp and switch, by allowing 12V back up the control wire onto the 'off' side of the switch.

It's exactly the problem I had with the midget after the engine swap, and is quite disconcerting! I added an N001 (maybe!?) diode in the smaller of the two alternator wires to stop the alternator feeding the switch from the wrong side, since that there is no more problem.

The alt can manage with 2 wires, 2 of the connectors on the 3 block thing on the body of the alt are joined together anyway. Sounds like the diode has been missed out when the conversion has been done; some alts have this particular diode in the rectifier pack, though the K-series one didn't!
Click to expand...

Thank you for your awnser. So, if I wire a diode into the position formerly occupied by the 3AW relay is should be ok? What I now (wikipedia) understand is that a Diode let's current trough say + to - but not - to +. If so, should the diode be rated the same as the fuse of this group (35A)? And what should and shouldn't it allow? 12V one-way and nothing the other? I'm starting to get horribly confused, not only by being new to car electronics, but also by the chaos of wires. I will take it to the parts shop and ask them!

This website is a great help for me as well, gives simple explanations about the functioning of basic electrical components in cars.
; http://www.bcae1.com/

Best regards,
Andries
 
Hi

The diode on the midget is wired in the small wire that comes out of the alternator. It has the '-ve' end towards the alternator, with nothing between the diode and the alternator, allowing the ignition circuit to control the ignition lamp but not allowing the live from the alternator to get back to the switch. Thus when the alternator is broken, there is nothing (0V) on one side of the lamp circuit and the lamp comes on.

I used an IN5401 (at least I think that's what it says on it), it just happened to be hanging about. As it only has to control the current for the charge lamp I guess the rating doesn't have to be that high.

However, to check it's not something else, start the engine with the alternator connector block disconnected and see if it still runs after you switch it off. Another option is that it's wired so that the alternator can power the coil independent of the switch. This can be tested with a resistance check between the alternator connections and the coil when the ignition is off.
 
1396midget said:
Hi

The diode on the midget is wired in the small wire that comes out of the alternator. It has the '-ve' end towards the alternator, with nothing between the diode and the alternator, allowing the ignition circuit to control the ignition lamp but not allowing the live from the alternator to get back to the switch. Thus when the alternator is broken, there is nothing (0V) on one side of the lamp circuit and the lamp comes on.

I used an IN5401 (at least I think that's what it says on it), it just happened to be hanging about. As it only has to control the current for the charge lamp I guess the rating doesn't have to be that high.

However, to check it's not something else, start the engine with the alternator connector block disconnected and see if it still runs after you switch it off. Another option is that it's wired so that the alternator can power the coil independent of the switch. This can be tested with a resistance check between the alternator connections and the coil when the ignition is off.
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Hi Rob,

Thank you for your reply, I will test it tommorow to verify the story but.. I can't get any diodes here anyway so I have to order them or replace the complete altenator with a new Lucas unit which is available at a workshop about 5 mins away. I'm aiming for peace of mind with this car and it has to, eventually, replace my Alfa so I guess I will change the complete unit and solder the wire mess near the old postion of the 4TR and 3AW units.

Andries
 
That would explain the excess voltage !
Click to expand...

The voltage should NEVER be that high.
Sounds like the voltage regulator in the alternator is gone.
Thats why the engine wont switch off.
the ignition is switching off the battery, but the altenator is still powering everything up.
 
If Midget is rememebering (or partialy remembering) n001 then it will be a 1N4001 diode but really any low current diode of a 1 amp rating will do, cheap as chips only a few P or cents, and readily available world wide from any electronic hobbyist shop.

Graeme
 
Thanks for all the replies guys!

I have Lucas ACR on order from a local workshop so I'll install it as soon as it arrives. Hope that clears the problem. Car is running fine with the alternator disconnected though, but still not able to turn the engine off without unplugging the lead from coil to the dizzy. Weber 500 floatchamber is waaaay to big to let her run out of fuel, would take ages. :D
 
Shame on me :oops: , I've replaced the fusebox with one from a '72 2000TC and that one had a bridge between fuse 1-2 and 3-4. To be more specfic, between a live connector of 1-2 and the fuel pump wire of 3-4. Off course, if energized everything from the 1-2 fuse charges the whole 3-4 fuse. 1-2 being the interior lights, strikers, map light etc. and 3-4 being ignition control! To basically, when I removed the key altogether the always live 1-2 circuit kept the engine running! Anyway, it's sorted now. Fuel pump was entirely disconnected before and was bridged over the ignition switch through the switch controlling the LPG system and fuel pump.

Stupid!
 
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