You have 3 relays. Disconnecting #3 would basically disconnect the charging circuit from the battery and could point to the cause. Does it blow the fuse when simply turning the key ON or when the key is turned to START?

OK, let's concentrate on the ammeter. Does this ammeter mount in a metal panel? or is the dash plastic? If the dash is metal, it is possible that the ammeter is shorting to ground internally, but don't rush out and buy another ammeter yet, there are some tests to do first. Do you own a multimeter (that will test volts, ohms, and continuity)? If not, you need to buy one before doing any testing. This may take several posts to get to the root of the problem. If the ammeter mounts in a metal panel, set the multimeter to Ohms or to "continutity" if you have that feature on your meter. This test applies ONLY if the ammeter mounts in metal. If dash is plastic, skip this test. Unplug the wires from the ammeter. Place one of the test meter leads on one wire post of the ammeter and the other test meter lead on a clean, bare metal part of the tractor. You should read "infinity" if using an Ohmeter, or "no continuity" if using continuity setting. Test both of the posts on the ammeter and they should both show infinity or no continuity. If either post of the ammeter shows continuity to ground, the ammeter is shorted internally and needs replacing. Get back with some test results. Alternatively, you can test for a shorted ammeter by connecting together the 2 wires that attach to the ammeter. If you connect the 2 ammeter wires together and the fuse does not blow, you have proved the ammeter to be shorted.

Batteries have a + mark and a -mark which should always be noted as to where the posts are oriented in respect to where they NEED to be when the battery is in place in the machine (and when buying the battery). Many batteries are offered in 2 versions (or part numbers). Batteries having an R suffix letter in the part number are the SAME as a battery without the R in all respects EXCEPT that the cable post positions (orientation) are Reversed. I hope this helps someone sometime when buying a battery and they encounter an R in the part number. I should mention that exposing these types of electrical systems to a reversed battery polarity event often destroys the voltage regulator (or a rectifier diode as the case may be). That may be checked using various tests, volt meter being a good one. Check battery voltage (using volt meter) with engine off, record the reading. Start engine and open the throttle until the engine is running at governed RPM. Check battery voltage again while engine is running. The voltage reading should have risen to a value of somewhere near 14 volts or a bit higher, or it should at least be INCREASING to a higher voltage that what you read with engine off. Symptoms of not charging will range from a battery too weak to crank engine.............to having the PTO clutch not engage or even "drop out" of operation when you mowing. This post was edited by mownie on Sat, Jun 22, 13 at 11:58

I have a 2006 Troy Bilt 42'' Super Bronco. Cranks right up but the engine revs really high and then dies. Every start blows the ignition fuse. I replaced the regulator and this seemed to fix the fuse problem, but the engine would only run for about 5 seconds, then die. Now, the fuse problem has returned, blowing with every start. Either way, fuse or not, the engine dies in seconds. It's got a new air filter, fuel filter, and spark plug. There don't appear to be any exposed or loose wires (which might cause fuse to blow). Again, it starts right up and dies immediately. What's especially odd is how high the engine revs up right before a fuse blows. I've never seen a mower engine do that and have no idea what's caused it.