I have seen special signal flashers with an extra wire coming out (earth) from memory or you can get load resistors that you wire in between the signal wire and the globe they need to be placed some where they can get air and away from things that can burn/melt because they get hot and you will need 2 one for each side.
I changed to LED bulbs and only had to change the indicator and hazard flasher units, no other wiring mods.
I had to try a few flasher units before I could get it all working though.
I did a complete change over to LEDs and found my stock hazard flasher worked, but at a slower rate. I left it alone. Used a neutral polarity flasher for the turn signals and grounded it to the ash tray frame. That’s the only changes I made.