/diy/ - Do It Yourself

Hey

anyone here familiar with low amp probe relative compression testing on cars? I bought myself an osciliscope and a low amp probe but when I disconnected the fuel injector fuse and hooked up my probe to the negative battery output I didnt get any readings what so ever except for the initial crank over when I turned the key, I have the probe facing the right way, also If anyone is good at explaining how to use this shit I'd be very grateful