Martin -- as long as you're not going with high wattage bulbs, you should be fine for the time being with standard h4 bulbs. Issue here is that, as built, all of the headlight current runs through the high beam switch on your turnsignal. This has been known to distort the high beam switch and cause you to randomly flash folks while driving. A relay is, in essence, a switch that is triggered by another circuit. You'd use the relay to bypass the high current connection through the turn signal/high beam and instead use the turn signal/high beam to power a low current circuit that "triggers" the relay to turn on/off the high beams (and headlight switch to turn on/off the headlight circuit.
Fortunately, there's an EASY solution -- our host sells a 911-specific relay kit that has exactly what you need to install the relays with (for me) easy-to-follow instructions -- here's a link
Headlight Relay Kit JWST911HLPR - JWest Engineering - JWST-911-HLPR | Pelican Parts)