vdo gauges/senders/wiring

i know this may be done to death on here so apologies.
firstly i have 3 vdo gauges volts/oiltemp/oil pressure.
volts is working fine.other two look to be linked up to this via various wires/connectors.from this im assuming they have been working at some point.
ive traced two wires from here into engine bay however this is where they have been tied up and aint connected to anything.
a few questions
1.are there only 2 wires reqd?
2.where do these wires go to?
3.which senders reqd.?

having searched tinternet most diagram/pics ive seen seem to have 2 connections above oil filter.mines only has 1(slightly behind filter) with a allen nut blocking off the other(directly above filter)?is this normal?
also read about connecting to the fitting on side of cylinder head.is this alternative or are both needed?

car is 1.8 carb 8v and vdo gauges are audi/vw items( no mfa on car)
any help appreciated guys
thanks bobby

just to follow on from above-
these part nos keep coming up 028 919 081d-low pressure-(head)
                                                   056 919 081e-high pressure-(filter)
                                                   068 919 081-high pressure.
are these part numbers for the standard senders or are these the ones i need to acquire.also where do the existing wires connected to these then go to.di i need t pieces or similar??

again if anyone can help simplify this  then please do
regards bobby