I'm testing my radio plug to find the Battery and accessory (switched) leads, so I have the key out of the car, and I touch my multimeter leads to the ground and then to what I assume is the "battery" (i.e. always hot) connection and it blows my radio fuse every time. I've got the multimeter set to test voltage. I've got the Symphony II+. I've tinkered with electronics for 15 years and this has me stumped. It's an auto ranging multi-meter, so I don't know if its the internal circuit of the the mulitmeter that's setting off the fuse.. Any ideas?

 

try a different DMM? that has me confused as well.. not sure why that would happen really..

 

It sounds like the + wire of your multimeter is set to measure CURRENT (A) vs. VOLTAGE. Look at where the red wire is plugged into - there are normally 2 options. It sounds like you want the other one, and double check your selection matches what you want to measure.

When you measure current, the two leads are essentially ONE continuous piece of wire, so by you touching one to ground, and the other to +12V, you've shorted the circuit, and thus blowing the fuse.