electrical gremlin

[chevyjeff59401]

I bought a 76 dually sometime back. I t has been sitting since 2003. I just put a motor in it and got her all ready to go. My predrive routine is to cjeck all lights. One brake light out after considerable attempts to repair and investigating this is what i come up with. If i just jump in it and press brakes no left light. If I turn key on sometimes light. If I turn key on and right blinker most of time left brake light. If I turn key on and taillights on most always brake light. If I fiddle around with a combo of all the above I can always get it to work til it sits for a while. What gives? Should I change column blinker controls. The truck has considerable amount of dust and grime in cab. Thanks for any and all help. Jeff