General

Assuming you mean your main headlights AND running lights on the same switch, be careful that the total current load doesn't exceed around 70-80% of the fuse/breaker rating for the circuit. As a general rule, a circuit protected by a 20A fuse or breaker should actually carry a maximum current load of around 14-16A (equivalent to 168-192W). The pre-headlight recall Slingshots used 2 Halogen H9 65W bulbs for the main headlight circuit and 2 H3 Halogen 55W bulbs on the same circuit for a total of 240W. This placed the circuit very close to the capability of the 20A breaker to protect the circuit and some Slingshot owners experienced loss of headlights during a ride or even experienced fuse block damage. The recall fix split the main headlight circuit into 2 headlight circuits, each protected by a 20A breaker.

LED bulbs will use significantly less power than Halogen bulbs, freeing more capacity for each circuit. Using 2 H9 LED bulbs at 36W/bulb means the center headlight circuit should only be seeing around 6A (72W/12V=6A), leaving room to safely add additional load to the main circuit and using 2 H3 LED bulbs at 26W/bulb for the outer auxiliary headlights should place around 4.3A on that circuit (52W/12V=4.3A), leaving even more room to add additional lighting. Just remember to keep the total current load on each 20A circuit below 14-16A.

After losing my headlights during a night ride, I rewired the outer auxiliary headlights to run off the Fog light circuit and reduce the load on the main headlight circuit. I also switched to LED headlight bulbs to further reduce the loads on the circuits. This has also allowed to run both the outer auxiliary headlights and the Canadian Headlights on the new split circuit for the outer auxiliary headlights and to run the LED lights in my MadStad Ultimate Bumper on the Fog Light circuit.

Bottom line - Always make sure the total load on a circuit doesn't approach more than around 70-75% of the total rating for the fuse/breaker that protects that circuit. This should leave enough extra capacity in the circuit to avoid overloading the circuit wiring/components as well as allow for variations in the performance of older components, etc.

NOTE - As part of trying to use circuit load numbers that leave a proper safety cushion, I chose to use 12V since that produces a higher current load number for a given watt requirement compared to using the typical 12.6V output of lead-acid batteries or the 13.6V produced by the Slingshot's alternator. If anyone notices any mistakes, please let me know so we can maintain the appropriate safety cushions.

I forgot to mention that while switches can be used to control the headlight circuits, State/Federal Laws require motorcycles to always have their main headlights on as a safety measure. Compliance with these laws is important when modding your headlight circuits.

SlingMods offers this kit for 2015-19 Slingshot to control all 4 Slingshot headlights which should also support adding running lights with a few mods - https://www.slingmods.com/slin…ight-bypass-kit?vehicle=3. I don't know if the kit will work with 2020+ Slingshots or if it can be adapted for them.

SlingMods also offers this kit if you want to add a switch to your Fog Light circuit on 2015-17 Slingshots - https://www.slingmods.com/pola…t-fog-relay-kit?vehicle=3. If you have a 2018-19 Slingshot, this kit should also serve as a base kit to add the Fog Light circuit and wiring to your Slingshot with some extra effort.