mine has a 9v battery in it, but i dont press any buttons when i plug it in, it just automatically comes on as soon as its plugged in. thats not just with my truck, its with all vehicles ive ever had it plugged into.

 

It is pin 16 but lower right on mine not like i said lower left and to confirm its powered key on or off i got 11.5volts. Now lets hope its a fuse.......

 

ok let me go check the pin again for voltage, i do see some corrosion on there, not alot though im guessing i shoudl probably give it a cleaning

 

Great idear sir....

 

im getting right around 3 volts out of it not 11.5 the pin on that side is full of crap though im going to try cleaning it off and see if i get proper voltage afterwards

 

The port on my 98 was screwed up like that. I had to jiggle the plug around to a certain position for it to work.

 

the good people of illinois air consider that "tampering" if you suggest they do anything like jiggle or even let you mess with it on their premises they are some dumb people

 

You should be probing the backside of the data link not going through the front as it can spread the connections apart but a good cleaning is a great idea hopefully its the issue. If not then pin 16 as we know should have voltage? pin 7 should have voltage it is the pci transmit or k-line. How many volts did you get? Now disconnect battery were going to check the grounds. Meter set to ohms pin 4,5,7 what you get?