You're in Ireland and you believe you need an oil cooler on a KZ650; why? Considering that the temperature in Dublin rarely goes above 70 degrees F I suspect an oil cooler would be a mistake. (See image below.)
Considering that the high temperatures during the summer in Maryland are always above 90 degrees F and that I have put 60,000 miles on my KZ650 without an oil cooler and have experienced no problems, I believe putting an oil cooler on a KZ650 in Dublin, Ireland is a mistake unless the bike is being prepared for racing.
If you do get one be SURE to get one that is thermostat controlled or you will be running oil that is too cold to burn off condensation, and that's harmful to the engine.
The oil pressure switch should not be affected by having an oil cooler since the switch is located in the right engine case near the timing advancer.
If you are bound and determined to put an oil cooler on it you may be able to use the pieces from a GPZ 750, but check first to ensure everything will fit properly. Ed
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