The left lead needs to be connected to the two red wires.

The right lead needs to be connected to the two white wires.

One or both of the leads can have damaged solder, resulting in poor connections between the lead and the wire ends.

De-solder the existing solder joints on the lead(s).

Solder the wire ends back to their corresponding leads.

Refer to this page if you need to brush up on your soldering skills.