This will help differentiate the different points that need to go into the wiring process. If the multimeter's reading is infinite ohms or OL (out of limits), this indicates the circuit is electrically open and this section of wire is most likely bad. If that's the case, proceed carefully as interior trim tends to be delicate and becomes brittle with age. The publication is available here for free. You're now going to test this length of the wiring harness for continuity, which shows whether electricity is able to flow through the wiring. Follow the ground wire and locate the point where it attaches to the trailer frame, which is … Having the kit in hand made it easy to understand the install procedure and wiring as opposed to just looking at a bad quality PDF file. If all the wires in the wiring harness are good, then the problem could lie in a section of the wiring harness between the accessory and power source that hasn't yet been tested. I have a couple of questions before I do the actual install. The pinnacle of wiring harness development was in the late 60s to late 70s, since then the wire size has gotten smaller, insulation has become biodegradable and the metal quality […] If your vehicle is not equipped with a working trailer wiring harness, there are a number of different solutions to provide the perfect fit for your specific vehicle. They also provide the vehicle side connector too which I don’t need as the tow vehicle already has that installed. After this process is accomplished for each wire in a wiring harness the next step is to layout the wires. Once the wire problem is located, typically the damaged wire or two can be repaired, or a new piece of wire can be spliced in. In short, a wiring system should be able to transfer a full-load of power without overheating. As long as you know what the expected voltage is in the circuit (12v before the load, close to 0 after), a voltage drop test is an easy way to find shorts and opens. Use the multimeter’s probe tips to touch the surface or area which you wish to find a damaged wire in. This is just a standard 4 way connector with a ground, parking, and signal or brake lights. To test the wiring harness, first remove the wires connected to the accessory. Repeat this procedure for the other wires in the wiring harness until the bad section is identified. Pull firmly on each end as if trying to stretch the wire. With a little practice the average weekend mechanic can learn to locate trouble in a wire with minimal testing. Consider the wire bad if it is any number of ohms or infinite ohms when the test lead is connected to another wire. How to Find a Bad Wire in a Car Wiring Harness Put on the safety glasses. Once assembled, wiring harnesses … Check for wires that have been pulled out and spliced with non weatherproof connectors. A low reading means that the circuit is closed and has no bad wiring, but if it reads as “Infinite” it means that the circuit is open, indicating that a wire is damaged. Check both sides of the fuse to confirm it is receiving power, if it's not hot at all times. Smell the rough spot or spots for a burned smell. The wire harness simplifies the building of these larger components by integrating the wiring into a single unit, or several units, for “drop-in” installation. Look for damage to the wire. Check the wiring at the base of the connector this is a popular place for the wiring to break. Instead, all this wiring is bundled together inside flexible plastic conduit to create wiring harnesses that traverse the vehicle through channels along a vehicle's sides, ceiling, and floor, hidden behind trim panels, carpeting and upholstery. Wiring systems need to be built to last. Smell the rough spot or spots for a burned smell. Next, check the fuse to ensure it isn't burned out and causing the problem, and consider these tips for checking fuses using a test light. (See blog “What is a HAD?”.) You'll find that electrical diagnoses require keeping a clear, calm head, and always start with the quick and simple tests first. Because these wiring harnesses run through tight spots, and are subject to tens of thousands of side or hatchback door openings and closings, there's ample opportunity for one wire in the bundle to break, or cause a short after its protective plastic cover has worn away. When replacing a bad fuse, make sure the new fuse has the same amp rating as the original. You might find a plastic trim removal kit handy. Corrosion also plays a big part in damaging an engine wire harness. and a dry-marker pen. Prepare the harness for a continuity test by turning the power off, since an open circuit could result in the meter getting damaged. Using a a new fuse with a higher amp allows too much current to flow through the circuit, potentially damaging components. In this case, where more than one component isn't working, use the wiring diagram to find shared points in the circuit. Here are a few key factors the differentiate good quality from bad quality: See how the connectors are connected. Knowing where to look and what to look for will be learned. Complete with a color coded trailer wiring diagram for each plug type, this guide walks through various trailer wiring installation solution, including custom wiring, splice-in wiring and replacement wiring. When restoring classic cars, often times the wiring harness also needs to be restored. I purchased a FK4Z-15A416-A wiring harness kit for my new 2017 Transit which has the open connectors on the fuel tank harness (14406). Clip the two test leads together and record the reading which should be infinite ohms. Expose the vehicle component that isn't working so that you can see where wires connect to it. He received his education in electronics and computer technology from Bell Labs. Step 3: Perform a continuity test with the aid of a multimeter, as this helps to find breaks and resistances in a circuit. The appearance of the diagram is a typical representation of how the wire bundling will ultimately look like. Use a fuse or breaker to cut off the power supply for the entire harness. The parts are insulated wire, connector housing, connector pins, wrap to protect the harness and mounting tabs. We're about to check for voltage. We don't see them, though, because that would just be unsightly and detract from a vehicle's stylish interior. Step 2 – Wire Layout. Carefully trace the wires back to the first connection point you encounter. Some harnesses take me one day to rewire while others take few days depending on the model. Given that I replace one wire at the time to eliminate possible errors and maintain original wire length for all plugs to reach their destinations repair takes very long time. Watch as we repair a wiring harness that had been chewed on by a few mice. All pr… Doing so will automatically narrow down the areas you need to visually inspect and test. This guide sheds insightful light on these Wiring Harness properties. If you suspect a grounding issuing, check for these potential causes and solutions to determine if there's an issue on the ground side of a circuit: If there isn't any electricity flowing to the accessory, the problem may caused by a faulty wiring harness or a bad switch. Disconnect the wires at that first connection point encountered. David Machado has written technical and home improvement articles since 2008. Wire Harness Durability. Put on the safety glasses. I have a 1996 Jeep Grand Cherokee 4.0L 6cyl. Here is the brand new generic wiring harness. In the year 1920s, engineers found out that binding many wires and cables into a wire harness allowed better protection against the adverse effects of vibrations, abrasions, shocks, and short circuits. Trace along the wiring harness feeling for rough spots in its outer tape or wrapping. Carefully trace the wires back to the first connection point you encounter. A stray wire strand, for example, may cause an intermittent short to a neighboring pin, crimp-caught insulation may cause intermittent changes in line resistance, and a wire with enough cut strands will simply fail the resistance check. Copyright 2020 Leaf Group Ltd. / Leaf Group Media, Auto Media: Working with Weatherpack-Style Connectors, Popular Mechanics: Repairing Electrical Wiring. And so it has happened. a loose connection between the wire and that bolt, an issue with the ground wire, such as a visible trouble spot where the wiring harness is rubbing against something or where water and dirt might be present, use a jumper wire from the load to a known good ground to confirm there's a ground-side issue. These conditions often cause the wire harness to stretch and contract causing undue stress, sometimes resulting in a broken wire. Since wiring harnesses are frequently installed in hard-to-reach locations, finding the exact problem area of the “short” circuit or “open” circuit can frequently be a challenge for a technician. It also needs to maintain that efficient transfer rate for a substantial period of time. Take your wiring diagram (see the Shop!) Make sure you write down which color wires come out of each hole. He received his Residential Builders License from the state of South Carolina in 1991. Wire Harness Diagrams. Step 3. This may require the removal of the wires from the protective plastic tubing. These are some drawings that should help with understanding the pin connector and keeping the wires in proper order. If a wiring harness is just a bunch of wires with connectors, how can you tell the difference between a good quality harness and a bad one? Visually inspect each wire, looking for any spots where the plastic covering has worn away, exposing bare copper wire. Find the wire being tested by its color. Set the multimeter on the “continuity" setting. Wire layout is just what it sounds like; an assembler takes each wire and lays them out – one at a time – onto a HAD. I've had some issues with a rough idle, and had a loose connector having to be zip tied to the computer because it was loose and causing stalling. Keeping serviceability in mind, there may be times when something needs to be removed, such as the center console in the example I just gave. 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