First off what kind of vehicle,second what are you hooking up 4 way flat ,6 pin round,7 pin round.makes a difference on wiring too.sounds like a fuse for the lights that are not working.if a new fuse is installed and it blows when park lights turned on then you may have a wire on wrong or wires touching each other.let me know?
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Britex flat seven pin plug wiring diragram
First off what kind of vehicle,second what are you hooking up 4 way flat ,6 pin round,7 pin round.makes a difference on wiring too.sounds like a fuse for the lights that are not working.if a new fuse is installed and it blows when park lights turned on then you may have a wire on wrong or wires touching each other.let me know?
Depending on what connector you are using, here is a link to the wiring diagrams:
http://www.etrailer.com/faq-wiring.aspx
You may have to use an OHM meter to test the leads at the tow vehicle side to verify correct placement. Good ground is essential too.