Unique tail light problem :-(

Recent problem with my 2000 cherokee sport I know you see this problem a lot but mine has me stumped read entire thread before telling me to do the usual plug and play repair. With headlights on my brake lights are all on (all 3 in back ) without me applying brakes. With headlights off when I hit brakes marker lights come on with them. So first I check and change bulbs all bulbs even marker light bulbs inspect and clean the sockets etc...it continues to do it.. next I remove headlight switch and apply brakes and markers still come on I replace headlight switch anyway because I was already there..still does it ...next I remove stop light switch turn on headlights all 3 brake lights still come on I replace brake light switch for good measure but it still does it...I read some things online about possibly being the hazard switch so I replace that all fuses and relays etc and it still does it..so then I'm like "challenge accepted" I start getting tricky on this thing I pop hood I pull fuse #19 (parking light fuse) on the fuse panel under the hood hit brakes parking lights still come on without that fuse in there.. so I put it back in I go to fuse panel inside truck #7 fuse (driver side marker fuse) and #23(passenger side) I pull em both I hit brakes and now only passenger markers cone on without the fuse even in there...how is this possible? I definitely have it down to a passenger side problem but can't finger if its a marker light problem or a brake light problem. It even does it without the bulbs even in there or fuses out etc. What I'm assuming is somehow the brake light is over drawing power then overflowing it back to the marker light but I could be way wrong and it could be something crossed with the marker light idk ...but what could cause it if I am correct?

have you checked and cleaned all your grounds?

it could be your relay

I have in fact changed relay...and I have changed 2 grounds that I have been able to locate my next plan of attack is to change passenger side tail light wire harness if that doesn't work then I'm completely lost

There is a common ground behind the spare behind the plastic that causes all kinds of weird things to happen. Check it and clean it.

I'm thinking with all this cross talk between circuits going on that we need to look at what the circuits have in common. Ground? Maybe...

Do you have an aftermarket Trailer harness? I have seen those go bad and cause interesting issues.

Has the vehicle been in an accident? Pinched wires are sometimes the result.

And lastly, the one thing these two circuits definitely have in common are the front and rear dual element lamps. There both the tail light and brake circuits come together. Did some person install a single element bulb for a dual element? Is one shorted internally?

-Ron

Problem solved today!! But I will answer the questions you guys asked me before hand just so if future people view the thread for answers everything is laid out... I don't have a trailer hitch or wiring and grounds were all good.. My problem in fact was a rotted hole behind passenger side wheel well must have let a ton of water and road salt in and destroyed my tail light harness. Wires were melted and destroyed at the plug.. I'm lucky it didn't go up in flames so I bought a complete harness with sockets attaches as well as the other side of the plug about a foot back and hard wired that in. I also cut out the cancer rust got some aluminum and riveted it down and filled the entire inside part of the wheel well with spray foam insulation to avoid future issues then I just put the interior panels back on and its as good as new. Thanks to everyone who commented for your input

Cool!

Most spray foam is open cell, which will trap water, and cause the.cancer to come back.