Fault alarm on my power inverter

I have a 400 watt Cobra inverter that is hooked to the rear cigarette lighter wires directly (half assed connection I know!)

For 2 months, it would power my tv and dvd player just fine. But lately the alarm intermittanty(sp?) goes off while Im running my devices. If I turn the bunk light on, the alarm stays on. It's not the inverter because I tried a back up one I have.

I know its alot of power, but why would it act up now and not two months ago.

Could the truck batteries be getting old??

Thanks

 

Yep, thats what it was. I thought they were tight, but one of the wires slipped part way out of the connector.

I-70 in Indiana is a rough highway, that probably did it!

Thanks!