Hi my name is John.
The two thing beside the switch that can cause this that I know are to load test the battery cable for high resistance, you can do a volt drop test either for the battery cables.
the next thing to do is to Separate G105 and G106 grounds.
For thr battery cables the resistance with a ohm meter should be .5 ohm or less.
here how to do a voltage drop test.
Let me know if you need more.
If I have help you,please push the accept button when were done.
Thank you for choosing just answer