Do you know what size battery cables it has?
A common problem is substituting automotive cables. They are too small gauge. It needs size 0 or 00 to work with 6 volt. Those typically can only be bought from a truck/industrial supply, not Auto Zone or Oreileys.
Try taking the switch out, get it where you can see it clearly. Look at the threads where the cable attaches. Sometimes if the cable has been arcing, it will melt the threads, char the surface where the cable tightens. When tightening the nut, be sure the cable end is compressed tightly against the back of the switch, and will not move once tightened.
Also look at the contacts. They will have some arcing, that is normal. But there should not be excess material burned or melted away. When reinstalled, be sure the contacts close tightly when the start lever is pushed fully.
If you want to check the resistance, best done with a volt meter "UNDER LOAD". Put each lead on opposite posts of the switch, it should show battery voltage. Engage the starter as if normally cranking, and read the volt meter. If making a good connection, the meter will be near zero. Anything more than about 1 volt indicates a poor connection. You may have to reposition the leads to pinpoint the area of high resistance, but that is the only true way to find the resistance. Using an ohm meter does not apply a load, and will give a false good reading.
Moving the amp meter lead to the battery will not accomplish anything, as long as it is the right size terminal to fit the stud and does not interfere with getting a tight connection. I like to keep the battery free of small connections, as they are more prone to fail from corrosion, getting gnawed on by jumper cables, or misplaced in the dark.