Tail light fuse blowing

I have a 1999 VZ800 and the fuse that controls the circuit for the tail light, side / postion light and the speedo illumination keeps blowing. It's a 10A fuse. I know I have a short somewhere but before I get my trusty multimeter out to look for it, is this a common fault and is there a particular part of the circuit I should concentrate on first. The fuse initially blew when I got caught in the rain. I've checked the bulbs / bulb holders, speedo, side and tail. Where should I look next? Thanks.

Most likely place is under the rear mudgaurd, there's not a lot of space and the tyre can rub through the tail light cable.

Thanks for the pointer. Once I’ve fixed this I either need to lose weight or stiffen up my rear shocks.

Have you tried adjusting the preload on the shox. with the back wheel off the ground I stick an allan key in the hole at bottom of the shox and use it as a lever to rotate the bottom mount over the cam. I think anti clockwise increases and clockwise reduces the preload. If you go to far you will hear a boing as the spring drops back to the lower setting or if it can't be rotated it's already on the low setting.

Could also be general corrosion thats eaten through the wiring under the rear guard.
Salt on the roads and lack of wiring protection is not a great combination. (Bikes definitely not designed for uk roads )
I had this before.