When you say "relay" behind the headlight, do you mean the black plastic plug that fits onto the three prongs at the back of the headlamp? If so and the headlamp is a sealed beam unit (just a large globe with three prongs sticking out of it, not a halogen unit that has a seperate globe and lens), you will need to replace the complete sealed beam unit (or upgrade both with halogen replacements for a better headlight all round).