So long as you have a real lightbulb in the circuit somewhere, there won't be an issue with the blinkers. I have real light bulbs in the front end, and I'm thinking about replacing my tail lights with LEDs. So long as I leave the front lights alone, the existing flasher will work as advertised.
On those aftermarket deals, the flasher is a seperate unit. They're too big to put inside the housing.
If you make the swap on the front end, too, then yes, you will need to use the "electronic"
flasher unit.
How slow is slow? 2 fpm? 1? That's a normal rate. In my experience, fast flashers generally mean that they're getting ready to die. A slow flasher is usually a good thing. If it's TOO slow, there may be a ground problem somewhere. Is it the same speed on each blinker, or does it differ?
The ground wire from the housing to the frame won't hurt anything, and may prevent future problems. Go for it.
