New here to Carloop, looking for some help

Looking to download Can bus from vehicles and run instrument panels on test bench. I work at a Speedometer shop, and currently a lot of vehicles will only do partial power up without seeing any can or non at all. I realize this might take some doing, we work on every make and model. And years up to 2019. We are in now means software engineers, just a mom and pop shop but have been here for 40 years. Any suggestions or help would be great. Thanks