its in the title

 

In-line module reduces the voltage for running mode, and increases the voltage for turn signal. Hence the dim and brighter appearance of the single filament bulb.

 

One bulb, one taillight, one filament,but it's also a turn signal? I gotta see this!

 

Hi. Welcome to the forum.

 

It can't

 

1990 FLHS here, owned from new. Our bikes have three 'tail lights', a large central one on the fender which is twin filament and functions both as a tail light and brake light, plus two indicator/signal lights, each with a single filament bulb which only flash when turned on. Please clarify what you are asking us about!

 

I have never heard of this. Thankyou very much! Where is this located at.

 

I saw that my brake light wasn't working. I changed the bulb.Checked it and it worked.I then saw that the marker lights were not on. Turn signals either. So i changed the bulbs to LED. I had replaced the brake light with LED. Apparently this really messes with everything. Gives the appearance of a wacked out dead short. So I changed back to incandesent . Thats when i saw single filament doing two jobs , running light and brake light.. one post said of a modulataor or whatever there is in line that I have never heard of.

 

Changing the central tail light to LED shouldn't mess anything up. Changing to LED flasher bulbs does, however, as the stock flasher unit is designed to trigger incandescent bulbs - LEDs take very little power and the flasher unit won't work properly with them. A modulator is an accessory which enables LEDs to work properly with a stock flasher unit.

 

I changed back to all standard bulbs and my rear running lights don't work. Turn signals do.