AFTER I had checked the bulb I was looking at various things and turned the key all the way to the Park position only to find that the light came on

After a fair bit of squinting at the wiring diagram it appears there's a 3A diode in the circuit for normal supply and switching of the tail light but the circuit for the Park light bypasses this.
Hence, "Sparkie Holmes" has deduced that this 3A diode would be a good culprit to replace.
But, I'm too pig ignorant to know where to go looking, complicated by not having a clue how big the diode might be physically.
Can some kind soul at least point me roughly in the right direction?
BTW I dunno why he's done it but the original owner had disconnected the "low beam" tiny little bulb and neatly coiled its cable - I assume the bullet connectors that used to connect to it are just directly clicked together somewhere with a yard of electrical tape on them. Amazing the things you find when you start poking around

thanks
Andy