TRA indicator... What is it?

[CrosbyFamilyFarm]

I've got a red light above my ignition switch that says TRA. The light never comes on but I'm trying to figure out what it means. Does it have something to do with glow plugs? does it have to do with TRAnsmission? I wish the manuals for these older models were a little more thorough (73 Ford 3550). Any help out there?

 

[Bigfoot62]

Sorry, but I don't have a clue.

Since this is a 40 year old commercial/industrial tractor, you might put a duplicate post in these two sub-forums:
Ford Vintage Tractors
Construction Equipment