3 light fittings at my sisters house have no Live feed. An attempt to renew a bulb has resulted in breakage of a baked batten bayonet bulb holder and I have gone there to renew it but find that there is no Live on the loop which has 3 red wires. Assuming a blown fuse, I have checked all visible fuses and terminal screws visibly and with continuity test. All are ok, so where can the break in the live be - any suggestions ?