Wiring a 1974 VW Karmann Ghia – Logik Relais 12V

Behind the dashboard is a tangled mess of wires, connections, relays, and terminals that ultimately connect at the fuse box. One of the relays in a 1974 Ghia is/was (this will depend on what you find in your Ghia) the seatbelt ignition interlock system.

1974seatbeltinterlockIn the United States, for the 1974 model year, the Department of Transportation mandated that all cars and light trucks be fitted with a system that prevented the vehicle’s engine from being started if the seat belts for both the driver and passenger (if present) were not fastened. This policy led to fierce public backlash culminating in the policy being abandoned in 1975.

In my Ghia, the logic relay was in place on the relay terminal but the seatbelt/starter interlock had already been disabled or disconnected. That is, I could start the car without my (or my passenger’s) seatbelt being engaged. I could not, however, start the vehicle if the relay was removed from the relay terminal. I would imagine that most Ghias and Beetles that still have the relay in place are in the same condition. They were hugely unpopular and were disabled en masse as soon as the DoT policy was rescinded.  I’d love to hear from someone (show car collector?) whose Ghia still requires the seat belts to be fastened.

So why all the information on 1974 DoT policy on ingition and seat belts? Because, as I previously mentioned, the logic relay was still in the relay terminal connected to a bunch of wires going all over the map. The purpose of this post is to document how I eliminated the relay while not losing the ability to start the car.

IMG_1690First off – how do I know which relay is which? Unlike the headlight and turn light relays (also on the relay terminal) the logic relay is a two block relay. It takes two positions whereas the turn and headlights take only one. It can be seen (although not completely) behind the clock next to the turn signal and headlight relays.  It has the following distinguishing marks:

Logik - Relais 12V

Ignition / seatbelt interlock (logic) relay from a 1974 Volkswagen Karmann Ghia


  • 133 919 431
  • Logik – Relais 12V
  • Bosch Germany
  • 0335 412 002




To remove the logic relay, firmly grasp both sides and pull up.  You will experience some resistance but with a little force it will come out cleanly. The underside of the relay (what I refer to as C and D blocks) interconnects at least ten different wires feeding the brake warning light, seat belt warning light, connections to the seat belts themselves, and most importantly the ignition cable to the starter solenoid.  This approach will eliminate the need for the logic relay.  It’s worth noting at this point that this approach will also eliminate the door buzzer and the brake and seat belt warning lights.  So, if those features are important to you, go no further.  I will be restoring my brake warning light in the future so keep an eye out for that post.

With the relay removed you can approach the wire removal from the relay terminal in one of two ways.  You can either remove them with a small, thin, flathead screwdriver (recommended) or by removing the fuse box and pulling from the back.  Pulling from the back is not recommended because it can damage the tabs on the fittings.  These tabs are used to lock the fittings into place in the relay terminal.  Unless you intend to replace all the wires with new ones with the tabs (not standard on most fittings from Amazon, etc) then I suggest you do the following:

  1. Insert the screwdriver into the small rectangle next to the terminal.
  2. As you push down with the screwdriver it should depress the tab on the fitting.
  3. With the tab on the fitting depressed, pull the wire from the bottom and the wire should come out of the relay terminal.
  4. Label each wire/fixture with the slot number it was connected to on the relay terminal.
  5. Repeat until all wires for the logic relay are removed from the relay terminal.
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