How to Add a "W" Terminal to ANY Alternator
You may be asking yourself, "What the heck is a "W" terminal, and why do I need it." Allow me to explain... The typical 12 volt automotive alternator has three windings that produce roughly 8 volts of alternating current each. This current is then converted in to 13.8 volts D.C. through the magic of science where it is fed to the car's electrical system.
1982 and up Volkswagens with diesel engines came equipped with a shift light that uses signal from one of the 8 volt windings in the alternator, along with high and low throttle switches and a control unit to turn on a light when it is time for you to shift to the next highest gear. This signal can also be used to drive a modified VDO tachometer from gasoline dubs, as well as an aftermarket tachometer (Requires the use of a diesel engine tachometer such as The Dakota Diesel Universal Disel Alternator Tachometer Interface.
Although I will be using this setup from 4crawler to drive my tachometer, I like having a shift light. In the following content I will show you how to add a "W" terminal to ANY alternator. Let's get started!
Remember: You can click on any image in the page for an enlarged view.
Here's What You'll Need:
| Part | qty |
|---|---|
| 14AWG wire | 12" |
| Heat Shrink Tubing | 6" |
| Zip Ties | 1 |
| Male/Female Insulated Bullet Connectors | 1 Each |
| Solder | some |
| Soldering Iron | 1 |
| Wire Strippers | 1 |
Step 1:
First off, ignore the pulley and fan in the picture, you never saw them. They do not, in any way, relate to this project whatsoever. Now that I have that out of the way, Remove the screws (follow the red lines). If they won't budge using a regular Phillips screw driver, use an impact driver (similar to what you might need to get the screws out of your front rotors).
Important: Match-mark both halves of the casing so you don't accidently put it back together wrong! Separate the t0p and bottom halves of the housing. This sometimes takes creative leverage/rocking.
Step 2:
Cut a piece of 14AWG wire roughly 12" long and cover 6-8" with a couple layers of heat shrink tubing. Make sure start an inch or so away from the end of the wire (see picture). This is to ensure that there is absolutely no way in Hades that the insulation will ever be compromised (causing a short and possible damage to the alternator).
Fish the wire through the back of the alternator. I put mine through here:
The goal is to get the other end here:
Step 3:
Strip enough insulation off of the wire that you can comfortably solder it on to one of the solder joints shown in the picture below. Doesn't really matter which one, I found the center lead to be easiest. If you aren't fully confident in your soldering abilities, read this article. The goal get the wire hot enough to melt the solder. Seriously, read the article...a cold solder joint here would mean taking the alternator apart to fix it!
Step 4:
Use a zip tie to secure the new wire to the wire from the field windings, and re-assemble the alternator.
Step 5:
Attach bullet connectors to the new wire lead and the wire that went to the "W" Terminal on the old alternator.
Congratulations! You're done!
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