What is the English past tense for 'on' ?

There isn't a word. For example, in the present tense you could say 'The light is on.' Past tense would be: 'The light was on.'

I think in most cases, for the word 'on' you'd put the word 'was' in front of it, to make it become past tense.

English permits creativity. Standard English does not use "on" as a verb, although it's opposite, "off" is sometimes used meaning "to kill." "Al Capone "offed" many competitors on Valentine's day."

By analogy, although it is definitely nonstandard, it is possible to be understood if using "on" as a verb, with the equally nonstandard, "oned," (pronounced as "owned") as the past tense. Other verb forms are also "produced" by analogy.

http://www.ling.upenn.edu/courses/Fall_2001/ling00...

Imagine two nonnative speakers speaking English while sitting on the couch.

She: "Get up and "on" the TV."

He: "How about you "oning" it this time,I "oned" it last time."

This is, of course, very unlikely, but I've heard much stranger things in international English. .

"On" is not a verb, therefore it has no tense. "On" does indeed form part of some verb forms in English, but it is the verb part which changes according to tense.

'on' is not a verb so it does not have a past tense.

He is on

He was on

it is a preposition