Do a visual inspection of all solder joints/ connection points. Look for cloudy grey solder and frayed wires. The solder joints can just be re-flowed with an iron and some 60/40 solder. If there are spade tip connectors take them off and clean the spade with contact cleaner or 90 percent alcohol and an old tooth brush, make sure the female side of the spade connection has proper tension, if not use some needle nose pliers and give them a crimp. edit: also use magnification when inspecting, at least 5x. Use a JEWlers head mount magnification rig and if you don't have one get one. they are key. Mine does 2x, 5x, and 20x and has three LEDs on the front that are angle-able. Paid 15 bucks for mine 10 years ago and cannot live without it.