Fuse keeps blowing

Hi,
The far left 16amp fuse in my '79 RS2000 keeps blowing, no idea why. Other day everything was running, car wasn't driven for a day, then went to drive it and found a blown a fuse which I replaced and blew as I was putting it in. I recently did install a new head but it uses the same wiring as previous head unit. Both the rear demist and dash dimmer were flicked for the first time in years.
How ever saying that, electrically speaking the wiring has not changed. I'm currently getting no head unit (if memory serves it is wired to clock wire, got no clock), no 4 ways (normal indicators still work), no horn, no dash light, still getting cigarette lighter and fan, exterior lights still work, not sure about wipers.

Have changed any globes ?
The mk2 were reknown for the probes in the globe socket being pushed over and shorting out, very often rear lamps,