Hi Michael The issue you have sounds more like a power/earth supply issue. I'm assuming the light lense and reflectors are in good order. The battery is good and no issues with the charging system. Start with the easy side earth or ground side. Connect a seperate earth from light to battery earth terminal just for test purpose. If light is improved then do the same the otherside. if good then you have an earthing problem.(use a slightly heavier gauge wire than your nomal lighting wire so there is no voltage drop). If no different move to power side disconnect connector to globe check and be sure which is the live terminal on the globe and connect a wire as before from + terminal on battery to positive on globe, light must be bright now. Ist check for loose or burnt terminals ie at connection to globe, battery power/ earth terminals.Check Battery to chassis connections for tightness. If easy to do so remove and and clean an re secure. Check engine to battery/chassis connections if all good you have to move onto the supply from fuse box and any connetions in between this is where it becomes more involved and would advise a qualified person to investigate. good luck