I have the Tecma toilet. The lights do not dim when flushing though the macerator is a powerful grinder/pump. You may try turning other appliances on/off as a test of the electrical system. Some fluctuation is normal; however, there should be only a slight observable variation, if any.
Check electrical connectors. You may want to see iff the voltage level in the RV is correct. There is an inexpensive plug into a wall socket meter.
There are power monitoring devices and meters that can help in determining if there is a power loading problem.
Fleetwood Providence 2008 40e
Ford F-350 4x4 Diesel 6.0L 2006
Honda CR-V 2006