All, just a bit of information to help those who undertake a weak light problem. I worked on a TR4A a while back with yellow head lights. Changed to Halogen with only marginal improvement. Next the alternator conversion, some help there, on to the relay wiring kit from Vicky Brit, not your best option, but effective, (you need to cut wires to get them into the head light bucket. Remember to soldier them back together). A big help, but all may have been for little gain. Next was the strip mounted near all the ground connectors, under the grill, running across the front, using a idea from one of the forum members. One large ground wire to the clean and sanded frame attached to the strip and the bullet connectors cut off and wired to the strip. Now we have bright head lights.
The relay is a good idea to keep the heat away from the switch but I'm not sure if fixing the grounds may have done the trick to start with.
Wayne