Reddog;
Check capacitor's charge up rate and it's charge voltage when the battery is just connected up to the truck. Meter pos on capacitor's positive terminal and the meter negative on the truck's negative terminal in the power distribution panel. You should see no more then 2/3 battery voltage and the charge up rate (RC time constant) will occure. An example would be if the source voltage were 10 volts, the resistance is 10 k ohms and the capcitance is 50 micro F, the RC time constant is 0-5 seconds. After 1/2 second, the capacitor will be charged up to 63% of 10 volts, or 6-3 volts. After another 1/2 second the capcitor will charge up to another 63% of the remaining voltage of 3.7 volts, leaving the capacitor about 86% charged and so on. Not having the truck's battery voltage prevents me from more detailed information.