Just blew brake light bulb, old bulb was 1157klf and new one is 1157LL. Looks like same bulb. Cleaned all connections put light tester on tail light assembly, light comes on when I press rear brake, weak and not as bright as tail light. Light comes on when I test hydro brake light switch. Put bulb in tail light assembly,comes on but no brake light. Replaced with new bulb to make sure, does the same thing. Its not blowing the bulbs its that the brake light wont work. Do I have to have, for some reason, that same bulb 1157klf bulb,which is hard to find at a auto parts store. Or do I have to go to a bike parts store for that bulb? 1157LL is a car bulb. Its a 1975 flh with a tombstone tail light, if it matters.

 

1157KLF never heard of it. This was on a 1975 FLH? Anyway, system is still a 12v concept and wattage might be the issue. Generally an 1157 bulb with offset pins should work. If indeed the bike is 1975 vintage AMF/Harley Davidson then it might be difficult to discern what volt/watt output was meant to be at the tail light. Suggest you check the ground points of tail light and ensure wires and connector are seated properly. An 1157LL should be fine with proper connection and output.