Join Date: Oct 2013
Location: Chilliwack, BC, Canada
Remove the dash indicator bulb. The problem is the way the indicator is connected to allow the single bulb to serve to indicate flashing in either direction.
The signals obtain power from the ignition switch to the flasher unit which is common to both sides. from the flasher unit, the circuit goes to the center of the right/left turn signal switch. When the signal switch selects one side to flash, it simply connects the circuit from the signal flasher to the selected side lights.
Each side has two signal bulbs, front & rear, which are powered from the circuit leading from that side's signal switch contact. The bulbs are in parallel which means that one can remove or burn out one bulb but the other will still operate because it has it's own path to ground. Depending on the flasher unit installed, the one bulb may not flash or flash at the correct rate because the stock flasher requires a certain current flow, equal to two bulbs.
When one side is flashing, the other side is disconnected so the signal indicator bulb is simply connected between the two sides. The indicator bulb is a tiny bulb while the turn signal bulbs are quite large. When the signal is operating to one side, the indicator is powered from that side and current flow passes through the tiny indicator bulb, then splits and grounds through the two big turn signal bulbs.
One can measure a small voltage drop from the indicator bulb current passing through the signal bulbs but the size of the bulbs is so different that the brightness of the indicator is hardly affected by having to pass through the resistance of the two big signal bulbs. One can prove this to oneself by simply removing the signal bulbs from one side. The other side will still flash normally but the dash indicator will not flash because it has no ground.
Installing LED into both front & rear signals creates almost exactly the same problem as removing the bulbs from the not flashing side. The resistance of the LED on the not flashing side is so great that there isn't enough current flow to light the dash indicator bulb. In fact, the dash bulb has such low resistance/is so big compared with the LED current flow that it allows the not flashing side to be powered through the dash bulb.
That's why I began by advising removal of the dash indicator bulb.
If you can live without the dash indicator, you're done.