Sounds like a ground issue. Instruments are simple. 3 basic connections (forget the lights for now)
Sender (S or G)
Many of the perkins panels
had VDO instruments so the Sender connection on the gauge may be marked "G" which is "Geber" or giver in German. This often confuses folks.
Check to see if the gauges are getting power. Make sure there is a ground to the engine or to a ground buss bar. The engine may not be part of trhe ground system if it is a euro boat.
The oil pressure sender will be about 1.5 inches in diameter and somewhere in the oil system near the oil filter
. The temp sender is in the head
(top) near the Thermoastat and will be a small brass unit Hex (Where you put the wrench)with one or two connectors. If it is a VDO temp sender it will have part numbers and max temp (Deg "C") stamped on trhe hex flats (Where you put the wernch).
If the senders have two connectors you likely have an ungrounded system where the ground does not go through the engine. Or you may have sender /warning light combo senders.
Look at the top of the oil sender. It may have a "G" (Sender) and a "WK" (Warning contact) that turns on a light at low pressure.
Do you know what gauges you have in the panel? If VDO they will have the Perkins
logo and a small "VDO" under it.