Wire nuts and common insulated crimp connectors are not good ways to patch wiring harnesses. A good solidly twisted inline connection (kinda like the old "western union" splice, soldered and sealed with a 2 inch sleave of heat shrink (possibly also sealed with dialectric grease) makes a connection that won't corrode and will withstand the moisture that is always a problem under the floormats of ald vehicles.
You want a good "gas-tite" connection.