Hold light blinks?
 

I have an Automatic transmission in my 1991 FC3C. There is a Hold light that keeps flashing, right above the Shift select on the Gages panel. What is that hold for? Next to the Shift selecter it has the normal P R N D S L. Next to the P D N it says Hold with and arrow going down and stoping at N. On the shifter nob it has to bottons One is big and thats for shifting. The other is small and I have an idea that it might be something like over drive but I don't remember over drive back then. Can anyone please inlighten me!!!!