I am currently installing a dash cam (Thinkware F770) on my car (2017 Ford Mustang EcoBoost). The camera comes with an optional hardwiring kit so it will stay on even if the car has been parked and the ignition is off.
The kit has three cables I need to connect. B+ (gets power no matter if ignition is on or off), ACC (gets power only if ignition is on) and ground. Those cables have to be connected to suitable fuses. I chose the B+ cable to the "Demand Light" (dome light) circuit fuse and the ACC cable to the "power window" circuit fuse.
In order to check which fuse has power wether ignition is on and off I used my multi meter. Ignition was off. I connected the black multi meter cable to a metal part on the car and touched the "Demand Lights" circuit fuse (10A). My multi meter was set to 12V DC. When I touched the fuse with the red cable, it threw lots of sparks that I feel was unusual for 12 volts. But the multi meter showed 11.x volts. After a while and with lots of sparks when touching the fuse with the red cable, it did not show anything at all anymore.
I checked the fuse and it was now blown. The dome light ("demand light") was not working anymore and worked again after I replaced the fuse. Is there anything in the process I did wrong? Why would a fuse blow by using a multi meter?