Grounding starter button issue

[hombres ruin]

I have a 41 coupe 6 V , at times the starter button grounds out and it all goes dead, once I re position the button it starts right up . The hole in the dash maybe a tad to big but the sides of the button fit creating that ground but at times it grounds out. I tried soldering a wire to the tabs on the switch then run it to the dash to ground but the solder will not adhere to that metal at all. I just got a new switch today. Any ideas on how I can keep a good ground. Thanks for your help