Gordon:
If you are losing "all power" , you must have a direct short . ie the hot side is touching a ground somewhere. AND since the guy probably did non run the signal light hot side through a fuse , you are burning no fuses(did you check the fuses?) If it keeps on happening and then starting again , there is a loose wire on the hot side of the power to something . Since it never happened before the new signal lights , suspect them first.
The only thing a bad ground to the signals will do is cause them to fail.(not work) It might be the ground strap for the engine failing, but since it was ok until recently, suspect the new wiring...
I have some experience in old English car problems like this.
David Potter
