Where to tap into for lights?

You must have a spare switch or two on your dash.. I did on my 2014 T-680.

 

You Can Always Add A Relay And Wire Them To Come On With The Rest Of Your Lights If You Want. The Switch You Use To Turn Your Marker/Running Lights Will Have A Switched +12v Out, Add A Relay To Prevent Overloading The Circuit. You Can Always Add A Switch To Run Them Independent Instead Of OR With The Factory Switch Depending On Your Understanding Of Electrical Systems.

 

Well It's Peace of Mind. You Might Get By Without One (Very Likely) But If One Of Those Little Lights Shorts Out It Shorts Your Whole Factory Circuit. The Relay Provides A Form Of Isolation From The Factory Circuit Per Say. Another Thing To Think Of Is A Year Or Two Down The Road If You Decide To Add More Lights (Or If You Sell The Truck And New Owner) Decides To Add Lights Unaware Of How They Are Wired, It Could Overload That Circuit. It's A Cheap Form Of Insurance To Separate The Aftermarket Lights With A Relay And Fuse, And Makes Future Installs Easier.

Advantages Of Adding A Relay AND Fuse:
(1) - Overload Protection.
(2) - Isolation From The Factory Harness And Electronics Which Are VERY Sensitive/Fragile.
(3) - Less Risk Of Blowing The Trucks Fuse And Killing Factory (DOT REQUIRED) Lights At The Same Time.
(4) - Future Peace Of Mind Installing Additional Lights Knowing The Circuit Is Meant To Handle
Additional Lights If You Choose And Not Having To Figure Out What Wire To Tap Into.

Potential DISADVANTAGES Of NOT Adding A Relay AND Fuse.
(1) - Short Circuit Of Added Wiring Or Light(s) Blowing The Factory Fuse, Killing Factory Lights.
(2) - Possibly Overloading Wires And Melting Insulation On Factory Harness.
(3) - Overloaded Circuit Causing Damage To Electronics In The Truck Like The BCU (Body Control Unit), ECM, ETC. Short Circuits And Overloads Are Extremely Unpredictable And While Not Likely Could Cause EXPENSIVE And EXTENSIVE Damage.

Again, You Might (Likely) Would Be Fine Without, But For Under $20 For The Relay, A Fuse Holder, Fuse, And Some Female Spade Terminals Its CHEAP Insurance And Peace Of Mind.