I'm sure it was just a ploy to make more money, but the service rep at a local dealer said that cutting and splicing wires on new bikes would have the bike throwing codes.

Looking at the Kuryakyn Bullet Light Rear Turn Signal Bar 5405, and it requires splicing wires. I would think everything would be plug and play these days but that's just me. Anyway, is there danger in doing this for rear turn signals only? Not sure I'd want to try it with anything more complicated than signals, though.

 

Anything involving the can bus wires can have issues if the wire pair is not twisted and matched to about 100 ohms impedance. Can is essentially a multi-drop computer network.

https://en.wikipedia.org/wiki/CAN_bus

Add:

Look at the Architecture section..

 

I've cut & spliced the front & rear turn signals & the LED headlight on my RK without any issues at all, harley supply crimp connectors for the wiring loom for the LED headlight & instructions tell you to cut into the existing loom, i prefer soldering over crimp connections.

 

I've spliced in (soldered) 2 LED turn signals plus an add on passing lamp without issue.

 

make sure you disconnect main fuse and battery. also as mentioned earlier you do need to have wires that match the ratings. I spliced and crimped (no solder) and it did throw a check engine light. I should have just reset the codes but instead I rode over the HD just in case it was something else..(after hearing about all of the exaggerated issues of the m8 engine) HD reset and cleaned up the wiring for me.. for a small fee. Lessons learned.

 

With the Can-Bus systems adding or reducing resistance could cause an issue because these systems are a a little too sensitive. That being said my Jeep has a Can-Bus system, and I have cut and spliced, and changed many things without issue.

Stick to the same wire gauge and do it right, and it should be fine.