I think your horn button scared it . . .
That flimsy relay only closes when the alternator is putting out.
a) analyze and label as necessary the terminals on the bottom of the relay. You need:
#30 goes to starting battery (+) . . . the only terminal on the relay that is not parallel with its edge
#87 goes to leisure battery (+) . . . directly across from 30 terminal
#86 goes to blue wire terminal that feeds your idiot light
#85 MUST be well-grounded
a) have kid start engine in neutral after you have attached the alligator clip of your simple test light to a good ground, and touched probe end to #86
b) kid easily revs engine just a bit (no more than 3,000 rpm). Test light should go on.