The Sarbat Khalsa was the general assembly of the Panth, held at Amritsar at Vaisakhi and Diwali, in front of the Guru Granth Sahib Ji at the Akal Takht. Any initiated Sikh could attend. A resolution passed there was a gurmata and was binding.
Decisions taken this way in the eighteenth century included the organisation of the Dal Khalsa in 1748, the striking of coin, the terms offered to Afghan and Mughal governors, and the campaigns.
The sardars who obeyed a gurmata commanded thousands of horse each and held territory in their own right. The mechanism worked because none of them could ignore it and stay in the Panth.
Ranjit Singh Ji held the last gurmata of the old kind in 1805 and did not call another. A general assembly is incompatible with a monarchy.
Sarbat Khalsa gatherings have been called several times since, in 1986 and 2015 among others, and their standing has been contested each time. The question of who may call one and whose word is binding has not been settled since 1805.
A gurmata is passed in the presence of the volume and that is where its standing comes from. It is not a vote in the ordinary sense and no source describes a count being taken. What is described is discussion until a resolution is agreed and then read out, which is a different mechanism from a majority and produces a different kind of obligation.
It could only work while nobody was strong enough to ignore it. Twelve roughly comparable powers facing an Afghan army every second winter is exactly the condition in which a common assembly is useful to everybody sitting in it, and that condition lasted about fifty years and then stopped.
It lapsed under Ranjit Singh Ji, who had no use for an assembly that could overrule him. Attempts to revive it since have been contested every time, including in 1986 and 2015.