I've got a 2005 F-150 5.4 and wondering is anyone knows what gauge wire runs to the license plate lights.

 

Because the feed might be required to power addl lights for a trailer , 14 gauge should be adequate.

The wiring for one or two bulbs over a plate ,16 gauge should handle that requirement with no problem.

 

I'm splicing the license plate light wire with new sockets and not sure which gauge heat-shrink butt connectors to use.

 

Locate License Lamp Right (E35) above, the power feed you see "20 BN" that means 20 gauge brown wire. Below E35 you see the ground which is "18 BK" that's 18 gauge black wire.

Factory wires refer to diagram above.
If you have aftermarket wiring and you don't have alldata software, you can still retrieve the gauge size by yourself.
1) Go to rockauto and enter your car's info and select license lamp connector as shown below:


You don't have to buy at rockauto, you go there just to retrieve the OEM part number or Motorcraft part number, unfortunately Motorcraft one didn't show up.
2) Randomly click on United Motor Products CON187 as shown below:


3) Now you see 1U2Z14S411BEA, you can search this within RockAuto again or Google.

Look above, now you see Motorcraft WPT1460 as well as the United Motor Products CON187 previously, perhaps rockauto search engine is broken, who cares.
4) Let's look at WPT1460 below:


As you can see above, Motorcraft WPT1460 (a repair harness) tells you to use 14AWG on both wires vs factory 20AWG for brown and 18AWG for black.

 

Thank you very much!

 

I entered 2002 above so the diagram is wrong. Here's the 2005:


Locate C462 above.
14 BR, 14 is the circuit, not the gauge size.
Below you can see the correct gauge size for 2005.


If you need to buy the repair harness at rockauto use 300461263265671655 coupon code (expires 6/6/25)
Please locate S403 and S401 above, S refers to SPLICE. So it's cleaner and better way to create the splice there than at the license lamp connector.