There are say four pins on the relay
For the sake of discussion;
One is earth or ground
Two is +ve feed (from battery or something live with ignition) this will require thicker wire.
Three is feed from source, in this case the main beam circuit.
Four is +ve feed from relay to spotlights which again requires thicker wire due to the current flow.
You can get a five pin relay which gives you a twin fed output, meaning you can run the seperatly to each spotlight, and would be my preference. Also you can get relays with inbuilt fusing, fail safe is always way to design.
Hope this is of help, it also makes life easier for fault finding, and future owner's to use existing colour coding to any circuit extension.
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