"I'm wondering if theres something stuck in the proportioning valve....."
I doubt this...., more likely a sensor or brake-light switch, (dirty connection) maybe a bulb out.
However.., you could back flush the porp. valve.., just in case a wasp built a nest in the exposed lines while sitting. (I've seen this B/4)
If necessary, freshening up the brakes on ea. wheel is cheap & easy...& they will work like new..!!

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BTW.., your main EB suppliers are; the sponsor of this board JBG, Toms Br. Parts, Wild Horses, James Duff, BC Broncos, LMC, & a few more that don't come to mind...

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