Electrical interference can come from high voltage / low current wires like spark plug wires. Low voltage, high current wires like starter, snow-plow, lift-gate and others. Any wire that has current flowing thru it creates a magnetic field around the insulation, when shut off, the field collapses. This magnetic field movement can and does cause problems. Low signal wires like ABS or VSS are small A/C voltages. A small amount escapes from the alternator rectifier and is present on the DC circuit. But, precautions are taken to re-route the wires away from others, twisted 9 time per foot, or shielded with metal tape and a dedicated ground wire. Grounds from the engine to the distributor are usually coming from the pinch bolt and clamp, but are found in the harness to the distributor as well. Certain engines had plastic distributor housings. Grounds from the battery to engine, battery to chassis / frame, battery to fender, frame to cab (Underneath vehicle) and ground from frame to bed are also important. Plug wires can fail as I have seen vacuum tubing rub through them into the core. Careful removal and visual inspection is best, plus one at a time or cable them. If you remove the spark plugs for infection, look for a thin black line running down the white ceramic insulator. If so, this is carbon tracking. Both wire and plug will have to be replaced. This occurs is engine runs lean for a period of time, like low fuel pressure. The coil builds as much high voltage as it needs to jump a gap. Dielectric grease works well here also. New GM's came with a dry version on each plug from the factory. To check if plug wires are arcing, get a spray bottle, put 3 table spoons of salt, 1 table spoon vinegar, two good squirts of dish soap, the remaining half of the balance with household ammonia and tap water. With engine running, in a low light area, spray each wire and the one next to it at idle. You will see the spark jump and hear the engine speed drop. Ask for a $100 digital multi meter for your birthday, then practice after watching some boobtube videos on voltage drop, resistance, DC voltage measurement. It will help as most all circuit in a vehicle a series circuits. Ohms law will help with "E" is electromotive force, measured in voltage, "I" is the intensity of electrons in movement, measured in amps, "R" which is resistance to the movement of electrical potential. It easy to learn after 20 or 30 years of daily practice. LOL.