If it were me, I wouldn't but a 36v rated controller. That's not to say you shouldn't do it! But I found a problem with this when i did my conversion.
As soon as your lead acid battery sags below 31.5 volts it will cut power to the motor. And on a lead acid battery that is bound to happen very quickly as soon as you try and accelerate hard.
I'd buy a 30 amp 24v
controller instead. They will work fine when "overvolted" at 36 volts and you won't know the difference.
I recommend the LBD 14 and have now used two of these daily for about 6 months at up to 1100 watts. Barely gets warm on the casing.
I think I have a third at home - could have a look inside the case in a few hours to see if it is potted or not...
If you don't want a keyswitch just short those two wires out. Or put a small switch across the two wires somewhere out of sight to deter theft.
Then fit a voltmeter in a spot that's easy to see to watch how much your voltage sags - use it to understand range vs speed. When you convert to LiPo you will see a much lower sag, but it will help you avoid going below 3.7v per cell and killing your batts. A much better fuel gauge than those throttles with an LED. And as dogman says it is important to understand the tradeoff between speed and range for your bike.http://www.ebay.com.au/itm/5PCS-Digital-Voltmeter-DC-4-5V-30V-Voltage-Red-LED-Mini-Digital-Panel-Meter-/270836381709?pt=LH_DefaultDomain_0&hash=item3f0f1b380d
i recommend this sort. Don't worry about the stated voltage range of that meter being 30v max, mine is accurate to about 0.25volts at 33.6 volts. Happily works up to 40v and there is only two wires on this one - just pop it across two the power input wires on your controller. You cna put a small switch in series to turn it off, or just leave it on, they use very little power.
And the warm red glow shows your e-grin as you quietly whirr past people at night...
Which country are you in Monkeychops?