Roman -

Just thinking outloud off my memory on how the + clamp is on our cars

I'm thinking a quickie test. Got a battery charger that puts out 14.4 V ?
Hook it up to the jump posts.

Test the leads in the trunk. However, on the +, pop open the BST and just check to see if you have power off the terminal under the BST.....if you are not able to spot the condition of the BST.

If you have power off the terminal on that, power would be pass through the clamp .