cant ping when adding secondary ip to 1 fastethernet interface on 1700 router

I am testing on a local router adding a second ip. when i add a
secondary ip in the same subnet everything works but when i add a
secondary ip in a different subnet i cant ping from or to the router. i
also try adding a second ip route 0.0.0.0 0.0.0.0 mynewgateway but that
did not work. I will change providers soon and i would like to make
sure that when they put the router in the new location everything will
continue working. can this be done?
thanks

 

(config-if)#no ip split-horizon

 

Thanks, I almost thought that was going to work. I was adviced to set
the default route as the interface and worked better but it did not
solve the problem. I will upload the configuration to the router with
the changes using tftp that is probably the best way.