The flasher problem in the +8 is at last solved,  and it only took another leisurely 5 hours.  In the process I learned that the flasher unit in R7429 is mounted under the dash (on the firewall) just to the left of the glove box. But that wasn't the problem.

I also learned that what is indicated on the factory instruction book as a hardwired ground connection from the flasher socket to ground is not; it's just the usual rely-on-luck connection to the body through the mounting screws.  But my newly manufactured test device (a bulb with leads soldered onto the hot and ground contacts) showed that the ground wasn't the problem. Due to the need to have a low-resistance contact, not just any old contact, it was necessary to do the trouble-shooting with an actual bulb, not a voltmeter.

I also learned that the proper replacement bulb for the flasher is a Lucas 382, for which Wagner makes what they say is a direct replacement, and that an 1156 will also work.  But the bulb wasn't the problem.

There is in fact a plug/socket connection in the hot lead just behind the front brake rotor.  You might think it would be, but that wasn't the problem.

The wiring diagram indicates a crimped connection involving the hot wire to the flasher, the blinker light on the dash, and the wire coming off the flasher switch.  Crimped connection?  Oxidation?  But where was it; it could have been anywhere in the harness between the flasher switch and the light.

British engineering to the rescue!  Knowing this crimped connection was sure to fail within the century lifetime of the average British car, Morgan engineers actually brought the three wires concerned out of the harness under the dash and crimped them right then and there, without tucking them back in. So when the connection fails, it can be replaced easily enough, if you know where it is.  Now you know where it is.  The analogous connection for the other side's flashers is just down the harness a piece.

Clipping the crimp and soldering the wires solved the problem.  For good measure, I clipped out the plug/socket and soldered that one too.

Jeffrey