Entirely electrical-related. And there is NO speedo or tach cables on any XB models. Both gauges driven electronically via the onboard ECM. The ECM receives coil pulse signals which trigger the tach....the ECM receives rotational signals via speedo sensor which triggers the speedo.
It's not coincidental that your 2 issues occurred at approx. the same time. And neither issue will dump an active fault code into the ECM historicals. Electrical gremlins almost never generate FC's. Your XB is now 16 years old and needs the following to try and resolve this:
1-Check condition of your new battery terminals and all 4 battery cable ends. Clean and tighten if necessary
2-Remove right side switchgear cover and clean and lubricate kill switch and connectors
3-Clean and lubricate ignition switch and its harness plug
4-Remove front belt black plastic pulley cover...separate every single plug...clean and lubricate...reinstall
5-Remove front plastic fairing/windshield assembly from its mount. Check every single plug and connector and ground wire for cleanliness and tightness.
6-Check every single ground wire. They are front cluster grounds....frame tie-bar...ECM...sub-frame harness to sub-frame attachment point...negative battery cable end to sub-frame attachment point
7-Check for the dreaded "main power feed red positive wire" failure. Wrapped in OEM harness at the steering neck area. There is a specific way to test it for continuity
8-Replace the KEY SWITCH relay. Click my name...click active posts...scroll down to RELAYS comment...click same. I list the part number and cross-references for all relays.
9-Lastly, the Ulysses debuted in 2005. The 2005-2006 models had a propensity for the seat pan to rub against the ECM and its wiring harness plugs causing cracks and damage to both the plugs and the ECM. With seat removed check your ECM for signs of tell-tale seat interference. A cracked/compromised ECM will cause precisely your identical problems.
Good luck and report back with findings.