just what the subject says...

If and when I plug my cell phone charger into the dash board cig lighter my coolant light starts flashing...  sometimes irregularly and sometimes regularly.  Freaked me out a few times before I put the combination together, now I just charge my phone from the 12v accessory plug under the passenger seat, but it'd be nice to fix this little wiring glitch next time I spend some time behind the dash.

Any suggestions on how/why/what could be causing this?

TIA,
Jon