Odometer not working, 1996 Nissan truck

I recently purchased a 1996 Nissan Pickup which doesn’t have a working odometer. I would like to repair it but, I called a Dealer Parts Department and they indicate there isn’t a cable listed for the odometer/speedometer. I also don’t see anything coming through the firewall, except the accelarator cable. The odometer and speedometer appear to be of the standard mechanical (cable driven)type, not digital electronic. How does this thing work, and how can I repair it?

This truck DOES NOT HAVE A SPEEDO CABLE. It is an electronic speedo and odometer. If the speedo works, only replacing the speedo/odometer will fix it. There are no parts available to repair these things.

They havent used cables since the eighties, its most likely the speed sensor.