No need for a loom, simply swap the headlight connectors and a simple link wire on the main beam switch. All covered in a thread on here before. IIRC wires are same colours, just swap the plugs. Saves cash!!
 
I've got a new (well , never fitted anyway) Simtec plug'n'play loom with extra wires for a set of spotlights. Willing to let it go..................sold my last F1 3 years ago and that was a genuine facelift anyway !!
 

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