1977 Bay Camper, 2 liter, FI

I installed LEDs for parking, brake and backup lights-they work great.

For the turn signal-they are blinking fast ( from what I read, this was
pretty much expected to be the case)

"the turn signals don't have enough resistance to blink. you have to add a
470 ohm resistor, or use a standard bulb at one end and an LED at the
other."

My question is:    Where does the resistor go?      Electronics is not my
strength, but if it is a simple answer I have the tools and basic skills to
do it.   Is there a way to do it without getting to the wiring under the
dash?    Can I put a resistor in line to one of the turn signals at the
spade on the actual signal housing?   Do I have to do all 4?

Thanks

stan