The basic wiring of a VW Beetle is very similar to many other types of European cars. Like most cars, with age, time and exposure, resistance can build up in a wiring harness and render simple circuits useless. So with basic understanding of European wiring standards, many repair tasks can be tackled. From the addition of a simple accessory to a complete wiring harness overhaul, following some simple rules will make for a successful repair.
First, we need to discuss a few basics regarding VW wiring. If you have spent any amount of time looking at a VW wiring schematic, you will notice that RED is used for constant power, meaning powered regardless of the ignition position, BLACK is switched power and BROWN is used for ground. The other colors will vary depending on the circuit but these three colors will cover most basic circuits. In addition to the color coding, a VW wiring schematic will have a number coding assigned to each terminal on a switch or other hardware component. These European terminal designations are also known as DIN standard and are used to determine a terminals use. First, take a look at the Bosch Terminal Designations.
These numbers are generally printed on the switch or other device for easy reference. As you work with DIN standard wiring, certain numbers will be seen more often than others. For example, a terminal designation of 30 always represents a direct connection to the positive battery terminal. While a terminal designation of 15 represents battery power when the ignition is in the crank or run position. As you become more familiar with DIN pin designations, you should be able to figure out the purpose without looking at a wiring schematic. Now when you combine the colors with the pin designations, you will notice a pattern. Red wires go to pin 30, black wires go to pin 15 and brown wires go to pin 31.
The next item you will notice on a VW wiring schematic is a number size assigned to every wire. The number wire size varies from 0.5 to 6.0. This refers to a European sizing that is measured in millimeter squared (mm²). European gauge wire is not easily obtained in America, so for replacement, it must be converted to AWG (America Wire Gauge). The conversion from European wire size to AWG is not exact. Using a slightly larger wire size is good assure against resistance and heat. For example a 1.0 mm² wire should be replaced with a 16 AWG wire which is 1.31 mm².
European to AWG Wire Conversion Chart
- 20 AWG 0.51 mm²
- 18 0.82
- 16 1.31
- 14 2.08
- 12 3.31
- 10 5.26
- 8 8.36
Now that we have some wiring basics covered, the next task is to gather the proper supplies for a correct job. You may need some or all of the following: Solid colored stranded wire, stranded tracer wire (wire with a colored stripe), brass open barrel German electrical connectors with installation tool, junction connectors and PVC plastic sleeving. No one vendor supplies all of the listed items, so here is a list of vendors for your supply needs:
- Solid &Tracer Wire: Riwire.com
- Brass Open Barrel Electrical Connectors: Goodspeedmotoring.com
- Open Barrel Connector Tool: Goodspeedmotoring.com
- Wire Junction Connectors Goodspeedmotoring.com
- PVC Polyvinyl Chloride (PVC) sleeving: Goodspeedmotoring.com
If your goal is to replace your entire wiring harness to factory specifications, you may decide a pre-made replacement harness as a good option. These harnesses fit good, wire colors codes are accurate and can be installed in about a day. Many VW vendors sell these, so see if this option is for you. Following either the instructions or a factory wiring diagram makes for an easy installation. However, if your vehicle is right hand drive or your goal is something custom, altered or improved, a custom made harness may be your best choice.
A custom made wiring harness will require much more time than a pre-made harness. It also requires an excellent knowledge of wiring and is not for the beginner. The vehicle pictured in the article needed some mild, but necessary changes. Our goal was to make these changes without losing the original factory look, being careful to follow the original DIN color coding exactly. This becomes vital for future repairs, especially if the vehicle is sold.
First, we needed to add grounds to all external light circuits. This is a very important step, as early VW’s use a body ground for these circuits. As we restore our cars, the mill thickness of paint diminishes the ability for the circuit to use the body ground properly. This results in poor lighting performance or sometimes an intermittent flickering of the effected light. Bright and reliable lighting is a very important item. Newer VW’s used ground wires instead of body grounds as this problem is prevalent.
Second, was to improve the quality of the headlamp illumination by adding two 40 amp 12 volt 4 pin relays. By adding a separate power lead for the headlamps and controlling them with a pair of 40 amp relays, you can eliminate the brightening and dimming of a headlamp that is caused with engine RPM. Understanding that relays are electrically controlled switches, we can use one relay to control both low beam bulbs and the other to control the hi-beam bulbs. Another feature is with a single separate 8 AWG power supply run directly from the battery to the relays 30 DIN power pin, you can also add higher wattage headlamp bulbs without overloading the system. Furthermore, by separating the power used for the headlamps from the headlamp switch, we were able to eliminate most of the amperage load and prolong the life of the switch. This info will describe the typical installation of headlamp relays.
For installation in a VW Beetle, please note the following. Pin 86 is easily drawn from the stock hi-low headlamp relay. Simply run the yellow and white wires from the hi-low relay to each 86 pin instead of the fuse box. Pin 87 of the relays then is connected to the fuse box like factory. Please note that pin 85 is used for ground. Why is a ground not PIN 31? Relays are used in many configurations, and pin 85 can be used as a negative winding end or a ground. This depends as to the purpose of the relay. In this case, it is used as a ground.
As you begin building your wiring harness, it is a good plan to have all your
hardware items, such as your fuse box, wiper assembly, switches and relays installed in the vehicle. This installation will aid in determining the length of wiring needed to complete a circuit. To help with the location of those numbered pins, take a digital photo of each item before installation into the vehicle. Simply refer to these photos for an easy reference. Many times these numbers are small and difficult to view from inside the dash area.
Building and installing a wiring loom can seem overwhelming at first. However, as you simply separate each wiring loom section it becomes easier to manage. The VW beetle has a main loom, left and right front lighting loom, and two short and simple tail lamp looms. Beyond these main looms, are short groups of wires between switches and relays. The main loom that spans between the dash and the rear of the car, have only 11 wires. I added two additional wires to power the headlamp relays and the electric fuel pump to this project.
To begin building the harness, make sure the lengths of wire is sufficient for the run. The main loom needs to be built outside of the vehicle. Take careful measurements so your loom is the correct length. I generally leave the wiring longer than needed so we can trim the length once the loom is installed in the vehicle. Once the length is determined, group the proper wires into a single bundle. Generally using a quality electrical tape every 12-18 inches will keep them strait and grouped. Once the wires are loomed into a proper group, slip the PVC tubing over the group. Next, install the main loom into the vehicle and adjust until it is located properly. Finally, we can trim the wires to proper length. Make sure to leave the wires long enough for maintenance. Then, install the brass open barrel electrical connectors. These connectors are identical to the factory connectors. Using the proper crimping tool assures a good connection. Now repeat this operation for each loom. Sometimes small and accessible looms can be pre built in the vehicle to determine length, removed for the installation of the PVC sleeving, and reinstalled for final fit. Be sure not to add any connectors until the sleeving is properly installed.
Be sure to test all wires once installed. Basic knowledge of an OHM setting on a multi tester is a must. Testing continuity is simple. Using your test meter set to an OHM setting, just place one test lead at one end of the wire, and the other test lead at the opposite end. An open or incomplete circuit will read as 1. A perfect wire will read as .000 the closer the number to .000 the better the continuity. On a 1967 and newer Beetle, this is a great way of testing the back-up light circuit before applying battery power. With the car in reverse, the switch will make contact and complete the circuit, and have a reading at or near .000. This continuity is what will turn on the reverse lights when 12 volt power is applied. While in any other gear, the switch does not make contact and is considered an open circuit, keeping the reverse light off. I also found using an OHM tester is especially important when determining the quality of ground points. I determined my ground points to be metered at .002, so when you consider the minor resistance within the body, this is a solid ground point.
Once the installation of all the wires is complete, it is time to test the system. Install all fuses according to the wiring schematic. Next, make all final connections, install a battery, and test. Test each item separately, headlamps, parking lights etc. I generally start with items that have consistent power. Once these items checkout, I will turn on the ignition to run position and test the switched items, such as turn signals and horn. If you have done everything properly, everything should work perfectly. If you have something not working properly, go back to the wiring schematic and double check every connection of the affected circuit. Generally you will find a wire or two that have been transposed. Once the correction is made, the item should work properly. If you have any fuses that immediately blow, please check that circuit for a short. An electrical short is generally a powered wire that is coming in contact with a ground.
With a basic understanding of wiring and some patience, European DIN wiring can be easy to understand and easier to repair. By removing wiring resistance and upgrading some circuits, your beetle will gain reliability and safety.