Hi new to old fords just savaging parts from a XG to put into XH. the ECU in the XH is playing up could I use the XG. The XG is a b mode and the XH is a D mode. thanks

Short answer NO.

Long answer yes,

The XG ecu runs a Log manifold (same as the low end XH) so that is fine, however the XG runs a viscous fan for the radiator.
The XH has thermo fans controlled via the ECU,
The XG ECU does not have outputs to run thermo's

You could manually wire up the thermo's and use the XG ecu, but thats a little bit of work.

If your on a budget, just get an EL ecu and this will work, however, the EL has been tuned for a broadband manifold, but will still work fine.

Thanks heaps Krytox.