In my travels I do a fair amount of straight up electrical work. I see my share of shorts, drains, and inoperative components at shops. I have always liked electrical work and it something for the most part shops tend to shy away from. Usually, tracing a short or getting into a battery drain is not as profitable as a brake job and can take up a lot of the techs/shops time. In todays vehicles there are literally hundereds of connections strewn throughout the vehicle. I wanted to share with you a couple I have encountered recently with a common theme-bad connections.
Let's disconnect the connector and check for pin deformation, etc.
Next up is a 2003 Toyota Sequoia that the battery would go dead overnight intermittently. The customer swears the headlamps turn on by themselves causing this. The shop has already installed a brand new battery and has never seen this phantom headlamp issue. I get called in and for the first couple of minutes of me manipulating switches and harnesses nothing happens. I turn my head and then look back and the headlamps are on and the switch is off and I have the keys in my hand. A second look and actually the DRL (Daytime Running Lamps) are on. DRL operation is controlled by the Body ECU. I hook up my Toyota Techstream scantool and I see no reason the Body ECU should be putting on the DRL lamps. I try to toggle the DRL relay on and off through the bi-directional functions of the scanner and they just stay on. Could the Body ECU be bad. Well, it is easy enough to disconnect. I do so and the lamps stay on. Do I have a stuck DRL relay? I don't think so since the vehicle should not have had the DRL lamps on to begin with key off. Hmm. Whenever I see phantom issues like this I think of two things-resistive shorts caused by moisture intrusion or bad grounds backfeeding. A quick voltage drop of ground circuits reveals excellent grounds. I am going for the resistive short. I start wiggling connections at the inerior fusebox which also serves as a junction box for many circuits including the DRL's and the lamps flicker. I trace the circuit to a particular connector at the fusebox. I cannot get this connector out of the fusebox. I have pliers on it and I do not want to break it off. I pull an adjacent connector at the fusebox and there are signs of moisture. There is green corrosion all over. I tell the shop owner he needs a fusebox. We finally get the connections out-here is the fusebox.
This next one is from a body shop I service. It is a 2001 Ford Windstar with no rear lighting. Front lighting is operative. This vehicle uses a REM (Rear Electronics Module) to control the rear lighting. It is nestled over in the right rear of the vehicle behind a trim panel-see below.
Finally, we have another fine GM vehicle. A 2006 Cadillac Escalade with complaints of no rear wiper and no rear defroster operation. I hooked up my Tech2 expecting to see a LGM (Liftgate Module) and start my diagnostics from there. No LGM showed up. A check of the wiring revealed no LGM on this vehicle and basically was old school from switch to wiper motor. With the rear liftgate open and the shop owner manipulating the rear wiper switch the interior lamps would come on or go out. That was my first clue where to go. Remember, phantom issues either resistive power shorts or bad grounds. I checked the ground at the wiper motor and depending on where the rear wiper switch was it was anywhere from 2.0v to 10.0v back to battery negative using voltage drop. Ok, we know we have a bad ground. The ground itself is behind the right rear interior panel. I really hate pulling panels when I do not have to. Lets check it at the liftgate connector that is easier.