Cabstar tipper stopped tipping?

[pdc95]

53 Reg Cabstar tipper, the tipper just stopped responding to the up/down control switch unit.
The switch unit has 3 wires the green wire has +12V and I assume that it is switched to 1 of the other 2 wires depending on which button is pressed.
When you press either button the +12V drops to 0v
When the main battery was flat the tipper still worked so does it have its own battery, if so where is it located?
Any ideas?

[Trevor]

SOunds like poor connections due to corrosion.

Chances are the battery terminals or starter terminals are corroded ....check these and go from there.
Don't forget to check all the earth leads and connections as well