scat track boom lockout safety failure

[wally b]

I have this 1980's 1700 Scat track which was bought out by volvo. The boom safety lockout keeps activating intermittantly which is irritating. Basically, when you get in and start up you put the safety arm down and then press the button on the control panel to operate the boom.. The boom then will work (raise/lower) intermittantly and it varies how long it takes for it to lock up. Then, you push the button on the control panel and the boom will immediately work again. This can happen several times in one lift or go for a while (minutes) before it will recur sporadically. There is no seat safety switch. I cleaned the safety bar switch and tested it for continuity and it works good. It is 'on' with eletric current when the safety bar is down. The puush button control switch on the operators control panel works good as well, and only flows current with a single push to activate currennt while depressed but spring loaded to be off after you release the switch. I assume then that there is either a wire short or a problem in a solenoid or controller for the hydralic valve. How do I locate the controller and test? Any source for parts? Thanks Wally