[turbobrnr]

All the safety switches have been bypassed and I need the wiring diagram to locate the main safety block.

[turbobrnr]

All the safety switches have been bypassed and I need the wiring diagram to locate the main safety block.

Murray 18 hp tractor model 3-39004 not getting any spark, but ran fine before I changed the battery and belts.

[crigby]

Hi,
You appear to have a very old machine; 1980's? It will have an oppsed twin engine and you can easily check the ignition for viability by isolating it from the frame of the machine. What that does is tell you if your problems lie in the engine or the tractor itself.
There should be a wire that is on the left of the machine and goes to a spade connector on a threaded post in a white plastic block beneath and almost behind the air filter box. Unplugging this wire (usually yellow but could be white) will provide isolation and you can now turn the engine over and check for spark. NOTE: the switch cannot turn the engine off if it cranks as that wire is the ignition ground!
If you have fire with the wire unplugged, then you will have to check the rest of the machine. If you do not have fire, then at some point in your changing the battery or something else electrical, you have applied battery voltage to that ignition ground wire which has blown the secondary windings of the coil. There is only one and it fires both plugs with every turn of the engine. Eight bolts hold the blower housing on, but you will have to remove the air filter, cover and base to get to two of them, if you should need to get there.
Peace,
Clarke