loss of power after device wired

I took my Zoombak gps tracker to a professional car audio store to have them attach the wiring kit to power the unit to a live wire in the car.

They said they wired it into the stereo wiring.  One strange thing I noticed is that the kit that comes with the Zoombak is a fused RED / black set of wires, yet after t he install, there is now a third black wire coming from the area where the other 2 wires went and that 3rd wire is connected to the chassis.  Why not just use the black wire from the kit to go to the chassis?

Anyway, what they did does seem to be powering the device, however, after leaving the audio store, driving 10 miles, and parking the car, the car would no longer start.  It had minimimal power and not enough to power the starter.  I took a guess and snipped the 3 wires, and tried starting the car again.  This time the car seemed to have more power, but still would not start.  After waiting about 2 minutes, I tried starting it again, and voila.. it started with no problem at all!

What could have  caused this problem? I stlll need to power that gps unit.  It  is labeled to have an input between 9 - 18 VDC and an output of 5.4 VDC / 750mA

I think that is about as much of a draw as a cigarette lighter.  The car is a 2002 Mitsubishi Galant.

We normally wire them through the ignition only, the "dropper" in the cig lighter adaptor actually draws more juice than the tracker itself (about 40 milliamps). Use a tubular lighter/power socket available almost any where, motor factors, Radio Shack, wire THAT to ground and ignition and plug in.

Well, I am puzzled why this problem occured by tapping into the stereo power.  The device doesn't draw that much power.  It can be powered by a USB port on a laptop computer.  The device didn't drain the battery of the car to make it dead.  Not more than a minute after I snipped the wires to the device,  The car had full power again.  Stereo's, A/C, and headlights all draw huge amounts of power, yet the car will still start with all 3 of those power hogs running - not to mention the various lamps in the car. 

The unit must not be detected.  I think running wires directly to the battery or to the ignition would reveal it's existence.  Fooling around with the ignition might also set off the air bags and/or car alarm. 

Also, I'm  sure the place that installed it would like to know why their work resulted in such a disaster.

Coincidental, Mits* electronics wouldn't detect this amount of draw on ANY circuit. I've installed trackers on a wide variety of cars and trucks, NEVER had a problem like this. * I have a Galant, (UK) Cat l alarm + R/S + Inbuilt (Alpine) Sat Nav + back-up camera + Parrot Bluetooth + GPS speedo and camera detector + often carrying 2 or more trackers wired up for testing AND extra built-in under dash power outlets for the trackers or charging up cordless tools. STD battery and alternator. My only problems? The original dash clock keeps failing, $225 to replace so forget it and the trap sensor on the driver's window thinks air coming into the car at 65mph+ is a kiddies finger, it needs resetting. Never had a flat battery or failure to start except when I blew a head gasket. Note all OEM problems.