Many different possibilities. Start with Steering Stabalizer and steering components. A bad coil can also cause the wobble. sometimes if the casters are at the wrong angles on the arms it can cause a wobble.
Death Wobble Solution! by Kel
Sure replacing the bushings, steering stabilizer and improving the suspension will help. . .but that is not where the problem lies. Take a look at the power steering motor itself, you'll notice that the BEARING in the steering shaft that connects to the pitman arm wobbles due to the constant force from turning left and right left and right all the time...this is due to the wear and tear of the steering motor. Jack up the cart get underneath and as someone turns the wheels left and right watch the shaft wobble. THIS IS YOUR PROBLEM! You must replace the steering motor!