In Australia, Deloitte’s shared this breakdown.

“On average, barely 5 per cent of a dealer’s profit comes from new car sales. The majority (about 50 per cent) comes from parts and service, while the remainder comes from finance and insurance (30 per cent) and the balance is from used cars (15 per cent).”

In the US it appears to be very similar.

“So where does the majority of a dealership’s profit come from? It’s not from car sales, at least not directly. It’s from the service and parts department, which accounts for the other 49.6% of the dealership’s gross profits, according to NADA.”

https://www.edmunds.com/car-buying/where-does-the-car-dealer-make-money.html