Some channels in the TAFL labelled as TAC for Orangeville actually cross reference to other fire services, my guess is for monitoring and mutual aid. Once you filter out the duplicates, you get some clarity from the TAFL garbage.
When mutual aid is in use (other services helping), monitor 154.130 (no PL) and 154.070 (OFM M/A)
Output / Input
Orangeville
148.0900 TAC (Simplex) P25 499 NAC (unverified -- will update when confirmed)
151.3850 FM (Paging) FM
151.3850 / 148.4200 Operations P25 499 NAC
158.9950 Mobile Repeater P25 499 NAC
154.0700 Ontario Fire Marshal Ch. 1 Mutual Aid (Simplex)
154.1300 / 157.4550 County Fire (Grand Valley) (91.5 PL)
154.1300 / 157.7250 Shelburne Fire (114.8 PL)
153.7700 Wellington Fire Dispatch
153.8000 New Tecumseth Fire (Probably deprecated, as they are now DMR)
154.3700 Simcoe Fire Mutual Aid
Shelburne
154.0700 Ontario Fire Marshal Ch. 1 Mutual Aid (Simplex)
154.1300 / 157.725 Operations (114.8 PL) FM
155.6550 TAC (Simplex) FM
461.6125 / 466.6125 Unknown: Same license as Operations. Says base access so could be something to do with remote dispatch
Grand Valley
154.0700 Ontario Fire Marshal Ch. 1 Mutual Aid (Simplex)
154.1300 / 157.455 Operations (91.5 PL) FM
154.1300 / 159.1650 Mobile Repeater (91.5 PL) FM
Hope that helps.