Anybody want to tell me what the heck I did ?

[mclaydigital]

Removed

[twiggles]

Your camera and flash will not operate in ETTL with a PC connection. For that, you have to have the canon (or knock-off) ETTL cord that attached to your hotshoe.

[twiggles]

see link:

http://www.bhphotovideo.com/c/product/498744-REG/Canon_1950B001_OC_E3_Off_Camera_Shoe.html

[msowsun]

With a PC cord there is NO communication with the camera. All that happens is the flash is told to fire when camera shutter is tripped. It is just like pressing the test button on the flash.

In ETTL mode the flash will fire a full power burst because it doesn't know how much light is needed. This is because there is no feedback from the camera telling the flash when to shut off the flash.

If you still want to use the PC cord, you must use the flash in manual mode only. There is no FEC (Flash Exposure Compensation) in manual mode. There is only power levels like 1/32, 1/16, 1/8, 1/4 etc. The -0.7 you saw was just a 1/3 stop minor adjustment to what ever power level you selected.

[Dermit]

All of what has been said is right on. With PC cord connection it's manual flash and you must dial it in. But also when shooting indoor and using flash regardless of manual or ETTL if you use Av mode there is a good chance your shutter is going to be way too slow... like what you experienced here. This is because the camera will still try to make the proper exposure and ignore what the flash is going to do. Most people switch camera to manual mode when using indoor flash and set the shutter to something like 1/125 and aperture to where they need it.

[Titus213]

I also read this problem all the time. Get the camera out of Av and into manual. Then manually adjust your flash too.

[danir.photography]

Time to get a meter that will trigger your flash.

[mclaydigital]

Removed

[PhotosGuy]

I'll keep experimenting with Manual mode Post #3 might help with that:
Tips for Xmas Ball Please (http://photography-on-the.net/forum/showthread.php?t=419399)