Hi guys, I'm puzzled here, so I could really use some advice. I've installed my car pc a few months ago and it has been running ok. I'm using a M3-ATX power supply with a constant 12+, ground wire and a + wire that switches on and off together with cigarette lighter when i turn on the ignition.

Only recently the pc has started to fail to turn on when I switch on the ignition. Weird thing is that since then the pc has worked only a few times, and even today turned on just 2 minutes before I arrived at work.
So I started to look for the problem.
- First I unplugged the pc from the car and plugged it in at home whith an external poweradapter delivering a constant 12 V. Everything went ok.
- Plugged it back in the car with everything connected - nothing worked
- With an extension wire I led the power adapter from my test bench to the car and everything worked ok. - So there is nothing wrong with the pc it self nor the external harddrive and other accessoires.
- So the problem should be in the power connector in the car. I took my volt meter and when I measure the voltage directly of the connecter I've measured 12V on the constant +, and on the ignition +.
- So everything looks ok. I plug in the powerconnector from the car into my pc and the pc doesn't start. When I measure the voltage again directly on the connector while attached to the pc the voltage drops to 1.5 Volt!
- When I measure the voltage on the connector while plugged in with my external poweradapter the voltage stays 12 Volt.

Can anyone explain what's going on? Where should I look next to solve this?
Thanks in advance.