Solder seal wire connectors for automotive use - worth a try?

...

Just a tip when doing multiple wires like say a 3 wire tach, stagger your cuts. Cut one wire at 3", the next at 5" and the 3rd at 7". This way your wire wont end up looking like a python that ate an alligator...

This could also reduce the risk of a short in the case of a less than perfect joint.