Where did you buy the new ignition switch, regulator and starter switch from? Was it Brian Hildreth or some other authorized Ingersoll dealer?
If you have the CORRECT voltage regulator, it will have three terminals on one side and one terminal underneath it.
In order for a regulator to function, it MUST be grounded to the tractor frame.
If your tractor is wired correctly, then you will have the heavy lead from the battery Positive terminal going directly to the UPPER terminal on the START pushbutton switch. A 12 gauge wire will be on that same upper START terminal and it will go the middle terminal on the regulator. Another 12 gauge wire will join the middle terminal of the regulator to one of the terminals on the key switch.
Therefore, if you have a TEST LIGHT that has a probe attached to a handle that will light up when power is applied and has a two foot long lead with an alligator clip on the end, then it would be perfectly normal to find power on the terminal marked BAT and the terminal marked L on the regulator. The 3rd terminal in that line up is marked F for FIELD and it goes directly to the FIELD terminal on the Start/Gen.
It would not be normal to find power on BOTH terminals of the key-switch UNLESS....the key is turned to ON. If the key is on the OFF position, then you should see power only on the terminal that comes from the regulator because the OTHER terminal on the key-switch is supposed to be connected to the + terminal on the ignition coil.
Now... let's go back to the START switch. The BOTTOM terminal on that switch should have a heavy gauge wire attached to it and going to the A or ARMATURE terminal on the Start/Gen. You should also have a 12 gauge wire attached to that same BOTTOM terminal on the START switch that connects to terminal on the UNDERSIDE of the regulator and another wire then goes from that same regulator terminal to the red GEN light. The other wire belonging to the red GEN light goes to the terminal on the KEY-SWITCH that also feeds the coil.
If you bought the correct regulator, key-switch and start switch and they are all functioning correctly, then all you need to do is follow the above wiring instructions to get everything connected properly. The only thing I did not mention is the LIGHTING circuit because it has nothing to do with starting the engine or recharging the battery. However, the lighting circuit is simple. Hook one wire between the L terminal on the regulator and one terminal on the light switch. The other terminal on the light switch goes directly to the two headlamps and as long as those lamps are grounded properly with good seal beams installed, the headlamps should light up when you pull the headlamp switch.
Your battery must be grounded to a clean spot on the engine. You can use one of the bolts that holds the hydraulic pump mount to the engine block.
In our TECH Library we have the Parts Manual section and there is a separate listing for the 100 Series tractors. Page 50 of the last PDF on that list of manuals, displays the wiring pictorial for your 195. If you want to find the problem, then you MUST trace all of your wiring so that it matches that diagram completely. You must also have a fully charged and TESTED battery under the hood. Don't assume anything. Even brand new batteries can fail in one way or the other and cause you all kinds of grief because you thought all along that it was good.
Do not get frustrated. You have to attack this in a methodical manner to narrow down what the real problem is.