Master fuse blows

[acres47591]

2013 725D. My 30A master fuse blows when I try to start the engine hot. Usually starts fine when cold. I had the starter checked and replaced the solenoid, but still did same thing. Did some testing and found that the solenoid trigger wire only had 8-9 volts. Changed the ignition switch. Now I have 10.8 volts on trigger wire, but still blows fuse when hot. Not sure where to go next.

 

[Hammermechanicman]

Clean and check both ends of the battery cables.
Connect your voltmeter from "s" start terminal of ignition switch and solenoid trigger wire with wire connected to solenoid. Turn key to start position and crank engine. Anything more than a half volt is a problem.

 

[Kneale Brownson]

Clean and check both ends of the battery cables.
Connect your voltmeter from "s" start terminal of ignition switch and solenoid trigger wire with wire connected to solenoid. Turn key to start position and crank engine. Anything more than a half volt is a problem.

So what is the problem and how is it solved?

 

[Hammermechanicman]

The test is measuring voltage drop across the connection from the "S" start terminal of the ignition switch to the terminal on the start relay. With the wire connected and the key turned to start you should measure very little voltage which means not much voltage drop. The more voltage measured the more resistance in the connection and this must be measured under a load.