Live alternator wire for delivery pump

[Deevo]

Hi everyone.
I've fitted a diesel delivery pump down beside the rear fuel tank of my Y61 TD42ti and wired it up using a relay. It's all finished bar locating a live feed wire from the alternator. For safety reasons, I want the relay to lose its feed when the alternator stops spinning and hence kill power to the pump. Can anyone clearly tell me where I could find the required wire to tap into? The relay is attached to one of the wiper motor bolts so ideally I would like a wire that is in the fuse box area but if it has to come all the way from the the alternator then so be it. I've also been told that I will need to fit an in-line diode regardless of where I get the feed from. Is this true? I hope I've explained what I'm trying to do well enough. Any help would be greatly appreciated. Thanks, Deevo.

[PeeBee]

I think you simply need to find a wire that is live when the ignition is on and dead when its off. Pull out a multimeter and start prodding around in the fuse box, or to home in on it look for the accessories circuit or the cigarette lighter circuit perhaps?

[the evil twin]

Best way to my knowledge is a relay off the Alt warning light.
Use the NO contacts of that relay to power the coil of the pump power relay.

Logic will look like this;
IGN OFF - Pump relay open, no power to pump
IGN ON, - Alt Relay energised no power to coil of the Pump relay, pump relay open
IGN ON & ALT running - Alt relay de-energised, power to Pump relay coil, pump relay energised, pump runs.

How you handle the initial delivery lift for a cold start will stay the same as now

[jff45]

I’ve done mine using the oil pressure switch to earth when engine is not runnng. Pump is fed through 30->87a when relay loses the earth. Pump cuts out if engine stalls.
I also run mine for 5 seconds while glow plugs are heating. The TB45 ECU handles that as it did for the old EFI pump but it can be done with a cheap eBay digital timer.

[mudski]

I’ve done mine using the oil pressure switch to earth when engine is not runnng. Pump is fed through 30->87a when relay loses the earth. Pump cuts out if engine stalls.
I also run mine for 5 seconds while glow plugs are heating. The TB45 ECU handles that as it did for the old EFI pump but it can be done with a cheap eBay digital timer.

Exactly what I did. Works a treat.