It can be difficult to get the 10 pin accessory plug into the 10 pin accessory port.
If you have a electric multi meter you can test the wiring on the remote. The the sleeve is the ground, the ring is the focus, and the tip is the shutter release. Without depressing the release test all the combinations of the ring tip and sleeve for a short. Half press the shutter release test the sleeve and ring for closed switch and the sleeve tip for an open circuit. Fully depress the remote release and both the tip sleeve and ring sleeve should be closed circuits.
If that fails, then maybe the cord for the 10 pin connection is bade and that is harder to test but you can find the pin outs for the 10 pin accessory and might be able to test the 10 pin cord.