Backuplights come on with brake lights!?

The backup lights on my 98 Blazer come on when the brake lights do. That is, when I apply the brakes, the B/U lights come on w/ the brake lights. Neat huh? I pulled the B/U light fuse and it went away. But when you put it in reverse, the brake lights work normally. Anyone heard of this cool little feature?
Thanks

Check the 409 ground right rear corner of body.
Feed back can be a bite on turn signals or brake lights.
The rear turn signals and backup lights share that ground circuit.
Or try a jumper ground wire into tail lights/signal assembly.
Or unplug one side of lights at a time.
Also check light green backup wire for 12 volts when you step on brakes.
Will they come on when using turn signals?
Do the turn signals work good front and rear?
Bad or wrong type of bulb will feed back to.
Is there a rats nest of trailer hitch wires under the back end?

Great response! I'll check that ground as soon as it stops snowing. I'm assuming its fairly self explanatory, I'll follow the harness back to find it. The trailer plug is ok, I checked that, the connections in it, etc. That's what I thought it was at first.
Another new fun part, the power locks don't work anymore. When I pulled the fuse for the b/u light, then replaced it... sometime in that process, all the doors locked and now the power locks don't work, in the vehicle or with the remote. If you pull the fuse, you can hear a click, like the locks are trying to engage, which is strange, because they can't lock the drivers door with the key in the ignition... Grrrrrr... I have electrical gremlins!
Thanks for the helpful response, hopefully it's the ground!

You are welcome.
Strange thing on the door locks.
The little green gremlin is working overtime on it.
Good Luck and let us know how it goes.
MT

Here's where we are so far - Still snowing so I haven't checked that ground yet, but where exactly is it?
I've checked all the bulbs(first time I've had those open since it was new) and all were fine. I pulled them all out anreplaced while the brakes were on, and that changed nothing.
It seems that the lights come though the body, do they come to the back in that same harness as the trailer wiring and the fuel pump wiring?
Also, the locks. They lock every time I hit the button for the rear lift window. Not when I use the button in front, not when I use the remote button for the window. Only when I use that button. So I disconnected it. Is this prone to failure? (prone he said - only 10 years old) Is it worth the 50.00 for that button or am I missing something else.
This forum continues to be the best website ever! :)

I found the ground for the rear of the body. Whoever put it on top of the frame rail that runs across the truck right behind the rear wheels should be beaten with a rubber hose. It was SO rusty I wan't sure if it would come off in one piece. I got it out, cleaned it, covered it all in dielectric grease and all is working fine. The concerning part is that the fuel full ground is also attached here. Brilliant.

Thanks for the help!

You are welcome.
And thanks for posting back with the fix and how it went.
Bad ground will cause feed back and do some crazy things.
Glad all is well and yes grounds are a bite and some times bad ideas on where the put them.
MT