My car is mechanically sound, but I have persistent electrical malfunctions with the power locks, power windows, and interior dome lights. They work intermittently and seem to fail every few months. I have replaced fuses and parts before, but the problems always come back. Based on these specific symptoms, what is the most likely root cause (like a bad ground, faulty relay, or wiring issue), and what is the correct diagnostic process to find and fix it permanently?
Kasozi
Hello Kasozi, persistent failure of electrical accessories and features such as central locking, electric windows and interior lights on an old car can be irritating. These electrical failures are more common if this old car is driven often in dusty, hot and sometimes humid or rainy conditions typical to our Ugandan setting. There are several reasons why these electrical gremlins come to bite when your car ages. The wiring and insulation can fail due to age. Exposure of the electrical wires in your car to the hot, humid and dusty conditions will make the insulation brittle, which leads to cracking and short circuits when the exposed wires with different polarity make contact.
The moisture from humidity and aggressive car wash jets causes damage of copper wires due to oxidation. The problem will be worsened when splices, poor insulation with ageing tape from previous repairs further exposes the wires in the different harnesses. Attempts to replace window switches or interior lights will only cause temporary relief as they are bound to fail again due to the damaged wiring. This can explain the intermittent electric window, interior lights and central locking failure. When the old car’s earthing or grounding points fail, this can lead to a break of the circuit. This problem is caused by rusting or corrosion damage or painting over of the car body earthing points.
Often, with age, ground straps between the engine, body and battery become loose. The many electrical systems that share the common grounds such as dash board electronics, audio system, interior lights, windows and central locking will begin to flicker or work intermittently. Extreme heat round the year from our summer temperatures will make door, window and wind shield seals become brittle or hardened. This causes leakage points where moisture and dust can penetrate the doors and windows. This moisture and dust will gradually damage the window motor or its circuit points, central locking actuators and door control modules.
The intermittent failure during wet seasons precedes total failure, eventually. Mechanical failure of circuitry switches and their relays can cause intermittent failure of electric windows, central locking and other electrical systems. Internal wear or damage of switches and cracking or loosening of buttons than operate them will cause gradual intermittent failure. Relays can become sticky overtime which leads to failure. As you replace one window switch, button or relay, another one is bound to fail down the road because of exposure to the same ageing conditions. It is like putting out a fire and another one starts elsewhere.
To resolve the intermittent electrical system faults permanently you need to carry out a comprehensive electrical system health check, rather than random repairs. Asses the charging system with an Alternator charging output and load test. Carry out a voltage drop test across the important circuits. Inspect all grounding points and evaluate their resistance. Finally check the battery age as well as carry out a battery load test. Renew or improve grounding connections. This can take away some of the persistent electric gremlins. Clean major earthing points, especially those that have been painted over. Sand them down to bare metal. You can upgrade grounding by adding grounding straps.