Wiring harness SIP Tutorial Episode 1

Created by Christoph Pflügler at 11:12 on December 27, 2021

Have you bought one of the SIP wiring harnesses for converting to different ignitions and are looking for more information? Or are you thinking about buying one, but are not yet familiar with the material? Then you've come to the right place!
To help you with this topic even better, we now explain everything you need to know with the "SIP wiring harness series", so that converting to tuning ignitions is even easier. We also give you useful tips and tricks for the installation with interesting background knowledge. In the second part of our series, we explain how to convert an oldie Vespa from AC to DC - i.e. with battery operation. The big advantage is that LED headlights, LED turn signals and various accessories can be connected to DC.

For this you need a kit consisting of the VAPE ignition, the AC wiring harness, an ignition lock, a battery and the most important thing: the cable branch for the DC conversion. You will also need various connectors, which are included in the delivery of the Wiring harnesses are included. The remaining parts can be found in the VAPE ignition accessories. You will also need a few commercially available tools such as side cutters, crimping pliers, wire strippers and a multimeter.

In the wiring harness workshop
Dr. Pflügler in front of a wiring diagram of a Vespa

Connecting the cable branch to the wiring harness

The following scenario exists: We have a built-in wiring harness, a rectifier, the battery and the auxiliary wiring harness. First of all, make sure that the alternator supplies the rectifier with the full wave. This means that the black and blue cable goes from the alternator via the wiring harness into the rectifier. With the blue cable it is relatively simple. Simply take the leftover single blue cable and plug it onto a black cable. Which black cable is secondary.
In the next step you will also need the black cable. If everything is laid correctly so far, there should be two black cable ends in the direction of the rectifier. But which one is the right one? To find out, measure both cables - and this is how you do it: First cut the cable lug of the black cable. Then strip the insulation from both ends. Then take the multimeter, set the control in the direction of the diode symbol and place the contact points of both diodes on top of each other. You should then hear a sound that confirms that there is continuity for the measurement.
Now the measurement is ready. It does not matter which cable is tested first. For this, the contact of the red multimeter cable is held to the end of the black cable and the contact of the second multimeter cable is held to the black cable on the alternator side. The cable that reacts positively in the measurement is thus the one in question and must ultimately be plugged into the second black cable of the rectifier.
But before this happens, the black cable that is no longer needed is insulated and tied back and the other cable that is still used is fitted with a cable lug and plugged in. Now the complete alternator shaft is connected directly to the rectifier.
The next step is to connect the positive cable from the rectifier to the adapter harness to the red cable. Now the three blue cables are plugged into the connector with the previously mentioned yellow cable.
Then simply take the wiring harness of the optional ignition switch and plug it together with the black and green cable to the respective colour.

Connecting the ignition switch correctly

Now there are four open contacts on the cable branch for the ignition lock. The green and black cables are opposite each other on the small contacts and the yellow and red cables are opposite each other on the large contacts. This means that in one switch position the current can flow from red to yellow, in the other this is interrupted. Thus the ground flows from black to green to the kill switch. The vehicle cannot be started.

Connecting the battery correctly

Finally, the negative terminal of the battery needs to be connected. But be careful: Only when it has been ensured that the light switch, the headlight, the horn, the brake light switch, possibly the indicator light switch and the rear light are connected and open connections have been insulated, may the connection be made. If this is not the case, there is a risk of cable breakage. In the worst case, this could even damage the ignition.
For the connection, a small cable is included that is first cut to length. With this earth connector we now go from the battery to earth, to which the regulator is screwed, and place it on top. Now the whole system is connected and the scooter can be operated on direct current.


Now the alternating voltage, which is always produced by the ignition, is converted into a direct voltage via the rectifier. This voltage goes out via the red cable and is fused to the battery. From the battery, the fuse goes to the ignition lock. This is connected through to the yellow cable and then runs via the blue cables into the wiring harness and distributed to the brake light, horn and light switch.

Important note: The connectors must be properly insulated. For this purpose, suitable shrink tubing and white connectors are included in the wiring harness package. This means that you are completely free to assemble the harness, taking into account that the connectors have been closed.

Christoph Pflügler
Christoph Pflügler

Christoph Pflügler is a master mechanic and has more than two decades of experience with Vespa. At SIP Scootershop, he is responsible in the 2nd level support for the tricky technical questions of our customers and he explains complicated contexts simply in technical blogs and tutorial videos.