lost power, won't run or start, no horn , flashers, no dash gages. on 1990 Dodge Ram 50

What can I check? Lost power, won't run or start, no horn, flashers or dash gages. Truck started and ran fine. 2 weeks ago truck did this and then after sitting for several days it started. I did replace the key reminder switch as someone thought that was it. Wrong. Truck ran this morning, cut out one time just before I got to work. then started after work and ran for a few minutes then died on the road. Had to tow it home.

Asked by for the 1990 Dodge Ram 50
Need to have alternator tested to see if is going out.