The early Type 3 ignition switches have a reputation for problems. Over time they tend to become loose inside and short out. If you have experienced this problem and haven't been able to find a replacement switch or couldn't figure out how to install one this article may help you.
Removal of the Column
To replace the ignition switch, the steering column must be removed. First start by disconnecting the ground cable from the battery. Loosen the two screws securing the fuse box and drop it down to gain access to the wires. Insert the key and turn to the "on" position, releasing the locking mechanism. Remove the horn button, disconnect the horn ring wire, loosen the securing nut for the steering wheel and remove it (#2 in the drawing below). Turn the steering wheel straight before removal so the splines on the shaft will be in the correct position when you reinstall it. Remove circlip on the steering shaft (#3) and spring. Loosen the allen bolt that secures column to shaft housing at rear of column (#5). Remove two allen bolts (#6 & #7) below at the center of the column. This will allow the column to be lowered from the dash. Now you will have access to the harness from the column to the fuse box. Make a diagram for quick reference of the wire connections. Early cars with "halt, garage, fahrt, start" modes on the switch will have six wires from the column harness: three of them are for the ignition switch and two are for the high beam switch in the turn signal arm. You will also need to disconnect wires from the front and rear wire harness connected to terminal block (#12). Remove the column as a complete unit.
Removal of the Switch
Remove the large circlip (#4) on the center of the turn signal arm, then gently wiggle the arm off and lay it to the side. The wires in turn signal arm do not need to be removed unless you're planning to paint the arm and column. Remove the two screws (#8) that hold the turn signal plate to the column. Pull it out gently and lay it to the side. Remove the securing screw (#13). There are three versions: either on top of ignition column, inside or above center of turn signal housing.
Remove the plastic access plug (#9) on the left side of the column. Use a soldering iron to remove the black/red wire (connection #50) from terminal block (#12) at the rear of the column. Remove the 2 screws holding the terminal block as well. With a razor blade, cut the harness insulation (#11) lengthwise taking care not to cut the insulation of the wires within. You can replace this insulation with 1/2" shrink tubing. Separate the ignition switch wires from the other wires and feed them out through the column. The ignition switch should be switched to "on" with locking models in order to free the switch from the column.
Installation of the Switch
Turn wires at a 90° angle carefully as not to pull the back of the ignition switch out (see "side view [A]" below). These wires must pass through the small ignition opening in the column which is only slightly larger than the outside diameter of the switch. Wrap the wires tightly at their ends with electrical tape and also wrap the end of the ignition switch overlapping slightly onto the switch housing (see "top view [B]"). The switch will not fit through the opening of the ignition in the column if too much tape is applied. This tape wrapping will help protect the wires and switch when feeding into the column. Bend the wiring harness to follow the access hole on the left side of the column ("top view [C]").
Feed the harness through carefully. Never pull on the wires; instead, just push from the ignition switch side using care not to pull the back of ignition switch out of the switch housing. Make sure to insert the key in the switch and turn "on" to pull the steering lock into the switch for clearance. Feed the wiring harness through the access hole to the rear of the column. Direct the ignition switch into the column by pushing the key slowly while directing the wires down from the back. For clearance remove the tape from the rear of switch through access hole on the left side of the column. Check for damaged wires or stripped insulation before securing the switch.
If wires become damaged during this procedure remove the switch, replace the damaged wires, and reinstall. Secure the switch with the securing screw (#13). Fit the #50 wire from ignition switch to the #50 position on the terminal block (#12). Trim the insulation and solder to the terminal. Trim the #50 wire from the ignition switch only if applicable (on switch with "Far, Start, garage, and halt" modes on it) and solder into the PL position on the terminal block (#12). Gather the #30 ignition wire, the two high beam switch wires in the turn signal arm, the #15/54 ignition wire, and the wire for the turn signal flasher unit. Install shrink tube over these wires, then seat into column below terminal block (#12) and reassemble the column. Install the column fitting and trim the #30 and #15/54 wires. Install electrical end connections and plug the column back in. User your notes for reference. For additional protection you can use some silicone on the end of the ignition switch terminals., but apply sparingly and then install the ignition switch end plug.
Take your time with this whole process. A good time to prep and repaint the column would be before installing the ignition switch, if you have an extra day or two drying time and can be without your vehicle.