Looking for engine running signal

[alinton]

My thoughts exactly. With pressure the switch is open, so o e side will be at 12v, which is what the alarm wants.

Now, to find the wiring!

What about 4WS? Surely that will only get power when the engine is on?

That gets power from ignition I think. That's going on;
Ignition on, goes through self test (you can hear the relays clicking)
Without looking at the wiring diagrams... I think it then just sits there until it's initially activated by the ABS (speed signal, but possibly something else as well?). I think the ABS only gives those outputs when it realises the engine is running, which I think it determines (indirectly) by oil pressure?


Looking at that oil pressure switch diagram you posted up (good stuff!)...
It's a normally open switch, but I think 'normal' is with engine running?
If so, that means with engine running, the switch will be open, which means there will be floating 12v on that line (it's not earthed, so the light doesn't illuminate)
When the engine stops (or oil pressure drops) the switch closes and earths that part of the circuit meaning you'll have 12v on the input side of the bulb and 0v (or near as) on the output side of the bulb.
That also makes sense as being the 'fail safe' way of designing the circuit (you would want oil pressure to 'break' the feed).

If that's right, take a feed from the output side of the bulb (or at the oil pressure switch itself) and you have the feed you need.
Make sure the input side to whatever you're connecting it to has a high resistance though, otherwise you'll have your oil pressure light fully or dimly illuminated all the time...

[alinton]

That's all brilliant guys. So I could either use what is effectively the cold side of oil warning light or the cold side of the alt warning light.

And yea, I'm pretty sure the inputs to the alarm are high impedance.

Just as well those lights are not LEDs!

Now, where do those lines appear at the ecu, or do they?

If they don't it's not too much prob, I can tap into them in the engine bay and route through the bulkhead via the same grommet that carries my amp high current 12v and the alarm's horn wire.

Thanks again!

[wurlycorner]

Alternator charging will appear at the PGM-FI ECU.

The oil pressure switch might not. That will feed across the dash to the passenger side, out through the A pillar, up inside the wing and to the plugs that sit on top of the chassis rail between the scuttle panel and strut top on the passenger side (I expect - haven't looked, but that's where the engine loom connects).

[alinton]

The PGM-FI ECU is the main ecu in the pass footwell?

[wurlycorner]

Yep