Talked to the tech.
He was quite puzzled he was not able to find a short.He showed me a stack of wiring diagrams.
I'll only bore you with 2.
He went thru the diagrams explaining to me every thing he checked and did. While he was talking , my eyes started glazing over and I heard myself saying, uhuh.....okay.......ya.......
I mean he could have been speaking Vulcan for all I knew!
He said he may have fixed the short just by moving all the wires he did while checking everything.
So he wants me to drive it, and see if it happens again.
If it does, he wants to divide the front from the back with 2 fuses, and try to narrow down the problem. See which end goes out.
And then do it again between 2 more sections. And so on till he gets it down to one thing, which could take some time since it only blows when it's raining.
He also suggested adding a new wire from the tail lights to a switch on the dash, creating a new line and fuse, so if it did blow again, I could hit the switch, and they would run on the other line, so I would at least have the tail lights.
Rewiring the entire lighting system would be very expensive, so he's trying to fix the problem, without major costs.
I can see my readers eyes stating to glaze over so I'll end this now.