When installing a battery cutoff switch there is an auxiliary contact to cut the ignition to stop the engine - any good ideas as to which bit of wiring to break into to achieve this? Any advice gratefully received
It already has one but I’m not sure they have wired the cutout - can’t quite see until I start pulling things apart. I was thinking about cutting the ecu supply - that’s what cartek suggest in there instructions for the electronic cutout The car will be used for trackdays and Timeattack Club 2WD
first thought would be see whats already been fitted before adding yet another cut out, most cut-out's simply rupture the positive supply immediately from battery
The main battery supply is definitely isolated by the switch, I just can’t see any ignition cut wiring. There are two 30A fuses on the battery post connection point, one of these will probably feed the engine bay fuse box. The problem is the aux contact on a cutoff switch is rated at 5A !!
Looking like a diy from previous owner I’d need see detailed drawing to get handle on what trying to achieve
The main battery cabling and the 3 ohm resistor is fine, it's the ignition cut I need assistance with - where to wire to / what circuit to interupt
Ah ok that’s good, all makes sense assume breaker 1 is to dissipate any residual current after switch off So what it your wanting to change ?
That's right for aux contact 1, any suggestions where to break into the wiring for aux contact 2, this will cut the ignition when the switch is operated.
You’re going need vehicle wiring schimatic to do that, is all this for an anti-theft device you’re wanting to install so if master cut out is activated the battery still won’t supply current to start vehicle? Also might need more than 3ohm resistor if going send 12v from battery to earth and around 100w
The 3 ohm resistor is standard supply by the switch manufacturers. It's already installed, I need to pull the dash apart to get it out but I've had a look with an inspection camera and one contact hasn't been connected and I think it's the ignition cut ! Just want it it to work as it should. There must be something easy access that can be cut and used. Don't have a wiring schematic, was thinking if getting the full manual of ebay
If you want the ignition to cut, break the main power from the battery, job done. If you run the engine and pull off one of the battery terminals the engine will stop
If you break the battery cable only won’t the engine continue to run on alternator / residual fuel for a few secs ? I.e. not an instant off.
I don't think so, as if you think the alternator would keep the engine running, it would also give enough power for the fuel pump so would keep running, the ignition system takes about 5 amps the fuel pump 3 amp Max the alternator output is 65 amps
Ignore my previous post I do think if the battery only is disconnected the alternator would actually keep the car running, that's why the FIA battery cut off switches include an ignition / ecu cut auxiliary contact to ensure the engine stops immediately - otherwise why would they bother with it ? Not sure how the cars electronics would cope with raw alternator output, it would probably cause some damage as the battery would normally serve a smoothing function.
you could just cut into the earths for the injectors, the ignition coils are linked 1-4 and 2-3 so that would be an issue in itself, injectors are individually powered but common earth, i could tell you what it is for a mk3 but for a mk2 i'm not sure
I'll have to do a bit of digging in the engine loom / under bonnet fuse box, there must be a fuse that will kill the ECU if removed. Not sure how much room there is in the fuse box to play with the wiring.
There's not much room in the fuse box area, cut the injectors, cut the earth and the engine will stop, if you start playing with the ecu you could end up spiking it and you could change/damage the program
Interesting that the injectors have a common earth - other cars I've tinkered with this deeply had a common positive supply and injector activation was achieved by the ECU switching to ground. Does the mk2 have an inertial fuel cut off switch? I'd personally be worried about things getting firey, so would look to cut fuel pressure - easily achieved by patching the auxiliary cut off into the inertial switch.
Not sure about the inertia fuel cutoff Still think ignition is the best to cut as with the battery disconnected and the engine not running all is dead, just need to find any easy cut in wiring to cut the ignition
What about cutting the +be supply to the ECU - pin M2 of the Sagem 3000 How does this sound ? Or The fuel system on the car uses the pump in the tank (not standard) as a lift pump to an OBP combined scavenge pump / pot. I could kill the OBP pump, that along with the battery being disconnected and the alternator being connected to ground by a 3 ohm resistor may do it
I used a battery cutoff switch, by interrupting the negative cable, moved Battery to boot, and have no problems, rather than interrupting Ign/fuel cables, but either way works.
The only schematic diagrams I can find are for phase 1 cars, it looks like the under bonnet fuse box changed on the phase 2 I've found the common feed to the injectors so that's one option, the supply to the ECU is another. We had a play the other night and found that disconnecting the wire from F3 at the battery post also stopped the engine (I believe this supply goes into the fuse box as well as one of the larger cables) Only issue appeared to be that the hazards flashed when reconnecting. They turned off with the hazard flash button ! I could do with a wiring diagram for a 2007 phase 2 car just to see how it all hangs together
