what is tandem lock and over speed on instrument cluster

[jc]

he all i just got my ebay tack today . when i took it apart to start kleening it up i noticed it had two warning lights buy the fuel gauge and a little light in the middle of the speedo gauge. the 2 by the fuel gauge say over speed and tandem lock. what the heck does tandem lock mean???i heard that speed warning clusters were hard to come buy .could i have stumbled upon a better deal than i thougt or is this thing from a dump truck. help please what is this . by the way i paid 165 shipped the needles have great color it needs a knew circut board and lens and it came with the harness.thanks for all input john