Ok I know it's a direct short but I am hoping to avoid the Smart A$$ replies so here goes...

Car has been in storage for the winter battery disconnected and periodically I will start her up and just do a couple mile run and put her away again. This time however I started her up on the first hit and after warming up I went to back out and hit the brake pedal everything went dim and the car stopped running like I turned it off with the key.

She restarted no problem touched the brake and down. So I know it's a direct short but has anyone experienced this before and thoughts on what to look at first?

 

Good luck with that one!
Has anyone watched the lights to see if there is any flicker from them? If they come on really dim briefly then it isn't a short or ground in the wire going there, I would tend to look more at an issue on a poor connection to the fuse panel, ie not getting enough feed to handle the bulbs and drops voltage too low for computers.

If they are doing nothing at all it could be a short/ground but it should blow a fuse and not drop power so low everything quits.

What happens with headlights, do they also kill the whole bus or do they come on normal and bright? You need to isolate if this is an issue just in the brake wiring circuit or an issue where not enough amperage is available to the main bus to handle additional load.

 

It will help immensely if you have or get the GM electrical diagnosis manual. You have a resistance connection whose brake light current causes the voltage to drop shutting off the ign, injectors, and ECM voltage. If you had a short, the stop/haz fuse would blow and the engine would restart and stay running and you'd have no brake lights. There are 9 red wires on the jump start bolt behind the battery, one comes from the battery positive cable and the other 8 go to a fusible link each and to many circuits in the car. One fusible link goes to terminal B2 of the firewall connector and then on the cabin side goes to a large splice in the wiring harness with 10 wires connected, one goes to the stop/haz fuse in the fuse block and powers the brake lights and two others go to the ignition switch. First measure the voltage on the jump start bolt while someone hits the brakes and see if the voltage stays at battery voltage. If it doesn't, then the resistance connection is the wire from the battery positive lug or a poor connection at the jump start bolt. Try cleaning all of the 9 wires on the jump start bolt and measure again. If 12v doesn't drop with brakes, then measure the voltage on B2 on the engine side and passenger compartment side and again at the 10 wire splice and again at the stop/haz fuse (brake applied). If you can't figure out which wire has the resistance, post your measuring results and I will try to help you further.

 

Ok then. I think you may be on the right track. Looking at some of the repair records for the car there was a similar issue before in the area of the jump start bolt. I started having a battery drain issue last season I had her out for show so to mitigate that issue I put on a quick battery disconnect and never really starting digging into the problem. Now it's a big deal so I have figure it out.

I appreciate the suggestions and I will definitely keep you informed on what I find. Not happening this weekend but it's coming up on car show season in the Pacific Northwest and I want her back on the road.

Thank You!