Ignition Wiring

[Joel]

I've somehow managed to wire my loom so everything is powered up at the first ignition point (first turn of the key after releasing the barrel lock), rather than the second point (just before cranking). So you turn the key one click and the fuel pump primes, power to ECU, etc.

 

It's not a problem in itself as everything works, the engine runs, and I don't have any accessories that require the igniton to be on, so I'm happy to leave as-is, but I just wanted to check I wasn't likely to be doing any damage frying circuits or that Mr.MOT inspector will have any issues with it?

 

It's wired (or at least should be) as per the attached image.

 

Cheers.

 

[knights_templar]

if everything works, can understand your reticence at changing things, however it is not "standard" or what driver other than yourself would expect getting into your car.

 

don't know if this is a fail for IVA

 

suspect mod is very simple, have you taken your ignition feed from the yellow wire on the ignition switch? that is auxiliary, radio, cigar lighter etc, move it to the Black/yellow wire and it should work as standard.

[Longboarder]

I don't know ofhand but I wonder if the ignition switch auxillary terminal is rated at a high enough capacity to do the ignition job. Auxillary pin also cuts out on cranking I believe. Best to move it as above.

 

Nigel

[Joel]

Thanks for the replies chaps.

 

I suspected a simple case of 'wrong wire' from the igniton switch, though interestingly that hasn't actually changed since I was running a bog standard carb setup, at which point it all worked as you would expect. This issue has only come about since I spliced in all the wiring for the injection setup, which makes me wonder if something strange is happening at the main igniton relay, or possibly even a knackered ignition switch?

 

In any case, you've convinced me enough to investigate further.

Thanks again.

[Joel]

Interesting development on this one - after a bit of investigation, sure enough I'd wired the supply to the main igniton and fuel pump relays from the accessories point. So I changed it to a switched-live supply, and now the engine won't stop! You can take the key out and walk away the engine just keeps running. This didn't happen when it wired through the accessories point. Can anyone suggest a reason why this might be happening or where to start looking for the problem?

 

Thanks again.

[Longboarder]

That's going to be difficult. To run on there have to be enough amps with the ignition off to run megasquirt, coils, and principally the fuel pump. It didn't do it with these on connection 1 of the ignition switch. All you've done is moved ign live and the fuel pump to position 2.

Was there anything already on position 2 which ign and pumps have now joined? Thinking anything they joined may feed current back to position 2 and out to the pump and megajolt.

What's the ignition light doing at switch on, running and when running on? Don't really know why I'm asking.

Have you got a spare ignition switch you can try to rule out a fault in the switch?

Bit baffling

 

Nigel

[Joel]

Hi Nigel,

 

It's a Premier Wiring Systems loom, and the ign position 2 (black/yellow) also feeds a fuse box with a common supply to the wipers; reverse light; heater fan.

 

The ingnition light behaves as you would expect after startup and running, but illuminates when you try to turn the engine off.

 

I don't have a spare switch - I did wonder if wiring up through a fancy starter button kit might bypass the problem?

 

This might be a red herring, but my loom fitting instructions says to take an output from the alternator to the battery VIA the starter solenoid. I'm fairly certain I've taken it straight back to the battery. Could that be a problem? From memory, the only wires going to the starter are the main big chunky battery cable and a blue/black from the ignition switch.

 

Cheers

Joel.

[Longboarder]

Blue/black is solenoid for cranking fed from position 3 on the ign switch.

Taking the main charge wire from alternator direct to battery pos or solenoid and then battery pos makes no difference.

Can you temporarily remove the wire from position 2 on the ign switch to the fuse box for heater, wipers and reverse light? It may be a back feed from one of them or an unsuspected wire in with them. Don't just pull the fuses. You must isolate that whole fuse box from the ignition switch. See what happens.

 

Nigel

[fry61]

Once the engine is running,is the alternator supplying the power ;back-fed via the connections on the starter solenoid? Maybe disconnect the alternator for a test run,it's the only other source of power.

[Joel]

Right, we're getting somewhere.

 

I wired it up so black/yellow ign position 2 was only powering the ignition circuit, and sure enough it starts and stops on the key as you would expect.

 

So, how do I isolate individual supplies to various places without getting any back feed?

 

It's probably not that significant, but in addition to the things I mentioned above (heater, wipers, etc), I noticed with this setup I also loose all power to my dash gauges.

 

Just thinking out loud, but could I use the accessories supply (fused) to power the heater, wipers, etc. Or is that really bad practise?

 

Cheers

Joel.

[Longboarder]

I would resist running the alternator unconnected. If you want to do that take the belt off so it doesn't turn, then pull the wires.

You have part tracked down the reverse feed. Reconnect the ign switch position 2 to the fuse box but pull all the accessory wires off. Run the engine. If not OK theres an unsuspected wire in there somewhere, either on the wire you have just reconnected or sneaking into the fuse box where you havent spotted it. The fuse box positive busbar doesn't have a constant live to it does it? That would explain the problem. Just disconnect it if it has and isolate/insulate it. That busbar should get an ignition live only from th ign switch position 2.

If however it's OK then reconnect heater, wipers, reverse light one at a time and see which one causes the running on to recur. Then you are going to be tracing just one circuit to see where it gets its constant live from.

Long shot guesses to check last if desperate!

Reverse switch isn't stuck on is it? Blown bulb so you haven't noticed.

Wipers have a constant live for parking sometimes. That might be the source.

 

Nigel

[Joel]

Think I'm making progress...

 

Didn't have time to be very scientific tonight, but I reconnected ign 2 to the fusebox, pulled out all the fuses, then put them back in one by until the engine wouldn't stop, and it seems to be that pesky wiper/reverse lt/heater fan connection. I then pulled the plugs from the wiper and heater fan respectively, and it still wouldn't stop. I don't know if that narrows it down to the reverse light (which is working fine), or not, but I feel at least like I'm looking in the right area now. Hopefully have a more thorough look at the weekend.

[Guest scrabster]

hi joel, this has got me thinking a bit, on my setup i have the rad fan on a manual dash switch with a led to remind me its on, when i turn fan off the led light goes out slowly until it dims then its out, i also had a bit of over run if i switch engine off with the fan still on.speaking to our auto electrician at work he says to fit a relay and it shouldnt do it. could your problem be the same as mine,seems the fan acts a bit like a generator until it stops.i have yet to fit relay to mine.hth.

regards,jess.

[Joel]

Hi Jess,

 

The fan in this case is the heater fan and not the rad fan. I have a similar setup to you with regard to that rad fan, with a tell-tale light on the dash that slowly dims as the fan cuts out, and it's controlled through an adjustable thermostat with relay. In any case, I'm not running the engine anywhere near long enough for the rad fan to cut in, so I don't think that's the problem in this case.

 

Cheers

Joel.

[Longboarder]

Sure sounds like you have narrowed it down to the reverse light circuit. Have you got a premier looms wiring diagram? Might be worth a look. The reverse light is very simple. Ign live to gearbox switch, gearbox switch to light, light to earth. How could that be wrong but it sounds as if there is a constant live mixed in with the wire between the fusebox and the gearbox switch.

Does your fuse box have a section of fuses supplied by ign switched live and a section supplied by constant live. Does your reverse light come on if you select reverse gear wether the ignition is on or off. That would confirm it. Then you just have to find it!!!! If it does then leave it in reverse with ign off and go through the constant lives wires out of the fuse box, disconnecting one by one to see if one of them puts the light out when removed. Then you have to see what else is supplied by that wire.

 

Nigel Sherlock