It appears I can get all I need to set up the new oil pressure gauge from the light switch:
"I just fitted newsouth guages the wiring I found easist I tookit from the headlights. White wire goes to headlight dimmer(blue and White wire)
earths there is a bolt under the streering column your see it when taking
dash off. The red wire I took from ignition live on headlamp switch
on the back. Black and white wire it is."