The plug at the back of the cluster has a removable back so you can see the wires & guts in the connector. You need to figure out a way to secure the wire in there.
I suggest finding a Contique in the local bone yard, any year/configuration will do, and pull out one of the wire/connector 'pins' and just snip off a length of the wire behind the 'pin' (for lack of a better word) and splice into that.
