Factory voided warranty

We own a whole fleet of Ford Rangers and they just not honouring their warranty. They claim because we have additional lights on our vehicles as they as used for security purposes, that they reduse to fix a broken turbo. Apparently we are using after market equipment which voids the warranty. Its just funny that they Ford Menlyn actually installed the after market products in their own work shop before we even took the vehciles. Never once was it mentioned that our light bars ontop of the roof will void the warranty. This after we have bought nearly 30 vehicles by them. Now my one vehicles turbo blew and they refuse to fix it under warranty. Ford will never see our business again i will rather take my business else where. We have played open cards with them from day one. They were well aware what our vehicles will be used for as the two way radios, the light bars, the signage and the cameras were installed inside their workshop. So for them to now after 3 years claim that we dont have a warranty any longer plus our extended warranty we purchase is now voided. So basically when you by a Ford - JUST DONT !