Do you guys use shrink butt connectors for waterproof purpose when doing wire modification of headlights in the engine room? Waterproof is required? Thanks
I've used them, before. But I prefer a standard vinyl insulated butt connector. Then, I coat it with 3M "liquid" electrical tape. When it's not available, just plain PVC cement used for PVC plumbing pipe does the same. It "welds" the palatic insulation on the wire together with the PVC insulator on the butt connector. These are great in salt water marine environments.
All the time, for added protection and peace of mind and so my wire job looks clean and OEM. I'd go as far as insulating the wire with wire conduits / looms. I don't think it's 100% required if you do a good job shielding your wires, but an extra layer of protection can't go wrong!