engine dies when fans turned on

As mentioned by 64 cuda and ramcharger. Check the main voltage line going into the MSD unit when the fans kick on. If it drops significantly, the MSD will shut down. Check battery voltage too.

Burnt has the right idea, stagger the start points for the fans if switched by a thermostat or run a dedicated relay to each fan. Sometimes the starting load is much greater than the run load.

Maybe disconnect one fan and see if the car reacts the same way. If the car continues to run when one fan activates, then you've likely narrowed the issue to a system load problem.

Good luck, electrical problems aren't a lot of fun.