i have a powermaster 8158 160 amp single wire direct to the battery. had one on there for 6 years and worked great. suddenly started to spike to 18 volts. turned out that the diodes and regulator(which is adjustable) were bad. decided to buy another one and send the old one in for rebuilding and have a spare. new one worked for a month flawlessly and then suddenly started doing the same thing as the old one. battery is fully charged and in good working condition,ground for alt. is good and main wire to battery is good. anyone have any input? thanks for any advice.