Re: Rear monitor
When I used to trouble shoot for a living, there were several things that I always considered first. #1 question is how quickly does it blow? If it is an instant flash when plugged in and gone immediately, then there is a chance of a bare wire or some other direct short. On the other hand, if the system works for a time but blows after a few minutes, that would usually indicate a problem in one of the devices that are fed by the fuse. If the fuse holds for several hours of use but fails only occasionally, then it may be related to just what is happening at the time it fails. That could indicate what is causing it by paying very close attention to any operation that takes place when the fuse fails, to see if it is always at that same operation.
Another tool to diagnose the problem would be to look for some way to seperate the loads to see if removing the back up camera will keep it from blowing, then remove the monitor to see if it will work and not blow the fuse? Does the fuse blow when the back-up monitor system is not in use? If it does it is a good bet that the problem is not in that part of the system. But to make sure, disconnect it. It is possible that some problem in the wire harness of the camera or monitor could cause the fuse to blow, even when not in use so make sure. Do not assume anything unless you test the theory. Most systems supply power from the monitor back to the camera so it too could be the culprit.
Unless you have a very accruate meter, measuring the current probably will not tell you very much. Before you do that, you will need to look in the manuals or on the particular item to see what it should draw as max. current. In a circuit that uses a 5A fuse, those loads are probably going to be in the range of 1A to 1.5A and a low price meter isn't accurate enough to tell most of us very much. If you have a meter like my Fluke 77, it is very accurate so the information may be helpful. You must put the amp-meter in series with the item you are checking to get an accurate reading.
Another thing that could cause this problem, but is not likely is that too high a voltage might. Since a fuse is a current device, high voltage will drive a greater amount of current and if high enough and above the designed operation voltage range the fuse might blow.
Make a few tests and come back with more infromation and we might be able to help more.