Halogen Upgrade
The MG originally came with sealed beam headlights and if I'm honest, the light output wasn't great, especially compared to modern cars with xenon or LED headlights. I therefore fitted some halogen lights instead of the old sealed beam lights. They are pretty much a straight swap with an extra wiring harness to convert the wiring to the H4 bulb connections. The most difficult part was removing the old lamps as I initially couldn't work out how to remove the chrome trim.
I eventually discovered that if you push down on the top of the ring you can pry the bottom of the trim off and then lift it up (thanks MG Experience Forum). Once the trim was off the rest was easy, remove the old sealed beam units, connect the new harness to the original connectors and reassemble. There is now a little extra wire but it's easy enough to hide away as it's out of sight anyway. The new lights were a definite improvement over the old but I'd been warned that the extra light output could tax the old wiring.
Headlight Relays
In order to help out the 1970s wiring I’ve installed relays for the headlights on the MG.
In an MGB the headlight wiring goes through the switch on the dash so the relays take the strain off the old wiring and the headlight switch doesn’t get warm any more…
I used a kit but essentially all you need are two relays, some electrical connectors and some automotive cable.
The wiring is simple,the diagram below shows how it was cabled up.
Originally, the blue/white wire went from the light switch to the low beam and the blue/red wire from the light switch to the high beam meaning that the full current went through the switch to the light. Now it's just a low amperage control for the relay and the main draw is from the 12v supply through the relay to the lights.
I mounted the relays on the radiator surround brace and I'm fairly sure that the lights are even a little brighter compared to just the halogen upgrade, but that just might be wishful thinking on my part after adding the relays into the circuit :-)