Disco 1 V8 fuel pump relay

Hi all, I've got an issue with the fuel pump not getting power all the time, I've traced the fault to a dodgy connection with the O2 inputs at the relay, one of the two O2 sensors has a wire spliced into it, without this wire it won't start, I've followed the wire to the inertia switch, does anyone know what that's about?

It's on a discovery1 V8 1998 auto

Ok Jack, as the “splice” is a DIY modification then who knows without the information on the colour of the wires involved, why perhaps the previous owner will tell you.

So from the fuel pump relay there’s a pair of white/orange wires in parallel, one to each o2 sensor, from each sensor you will also find a blue wire going to their respective terminal at the efi ecu., you may not see the colour as this wire is screened, there’s a third wire at each sensor with is earth.
So if u have a dodgy connection at the relay just repair it buy remaking the connection + replacing the relay if necessary, simple.
The fuel pumps earth connection is via the inertia switch, so why there’s a spliced connection there who knows, so what colour wires is the splice terminated from and to ?
White/purple is incoming from the pump at the inertia switch, the other wire is black so to earth... if the switch is activated the fuel pump stops.

Sorry I didn't make my post very clear, someone has spliced a wire from the O2 sensor white and orange wire to the wire from the inertia switch, without this wire from the inertia it won't start. I've taken the O2 wires out of the relay plug for now and just fitted the inertia spliced wire into the 87a pin on the relay, it starts fine now but I'm concerned as to why the spliced wire is even there and why doesn't it run without it

Ok, both the white/orange wires should be terminated at the fuel pump relay pin 87a, nothing else, then if the relay is functioning correctly it will supply 12v onwards to the o2 sensors.
It’s possible that there isn’t any voltage at pin 87a , then who ever it was, trapped into the fuel pump supply to pick up 12v which is taken from the fuel pump relay on pin 87.
So you should find 12v on both pins and if not check the relay and replace possibly.

So guessing... is it because there an issue with the pumps original wire and so modified the wire to feed 12v the pump as thats what the splice is doing, providing voltage from pin 87a.

But first terminated the fuel pump relay correctly and its job done there... then find out why there’s a 12v link to the inertia switch as this switch only removes the fuel pump electrical earth in a crash.

So the relay should provide 12v to pin 87a to feed the O2 sensor?

I'll look into it when I can, I've replaced the relay with new Bosch item but that made no difference.
I've remade the connection with the mystery wire to the O2 wire and it runs ok but I'd like to find the original fault and take the odd wire out.

When the fuel pump relay is energised, it will provide 12v to pin 87 and to pin 87a.