95 Ram 3500 4wd not working

Anyone have any ideas where to start 95 Ram 3500 cummins auto trans.The lever moves into 4wheel high & lo but the indicator light doesn't come on & its not in 4wd Worked fine last winter.
Thanks

Vacuum leak?

That's what I'd check for, including the steel lines and plastic and rubber connectors etc. Think they have some steel lines here and there that rust like the brake lines.

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That's what I'd check for, including the steel lines and plastic and rubber connectors etc. Think they have some steel lines here and there that rust like the brake lines.

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Yes 2 steel lines that run along the pass side frame rail from the trans X member tothe font axle.

Take a close look at the rubber connectors that go from the steel lines tothe plastic lines , if they are soaked from a trans or oil leak they can swell and lose their seal .