Exterior LED lights upgrade

[Jaytibee]

Hello all.
I am running a 2005 Jayco Class C Granite Ridge with the Ford E 450 chassis.
I actually just installed 1157 led's for the park, brake and turn signals and 1156 for the reverse lights. 1156 work fine with no problems. 1157s another story. I cannot get the park lights to come on. Brake and turn signals work and I will install an updated flasher to solve the normal hyperflashing problem. Has anyone upgraded to these leds and been able to do it succesfully ? Is there a special flasher with circuitry that solves this problem ? or are there other types of Leds that work ? Any help on this subject would be appreciated. John