This past weekend I installed an on/off switch for relay 605. For those who are not familiar with relay 605 it is the servtronic steering boost relay. Basically this relay is suppose to make the car easier to turn at low speeds and while stationary. In reality it boosts steering all the time at any speed. Relay 605 is located under the steering column and there are numerous posts in this forum on how to remove it. A word of caution here...it is easier to remove than it is to put back in. The steering with the relay removed is much tighter and in my opinion more responsive. It feels more like a sports sedan to me vs. a big luxury sedan like the Lexus 400. It actually reminds me more of a Porche or the Lexus GS. However my wife did not like the fact that when parking it required more effort to turn the wheel. Please note with the relay removed or turned off you still have power steering but it is more akin to power assist steering.
As they say necessity is the mother of invention.
With this in mind I got the wiring diagram for the relay from my dealer and asked the tech if what I wanted to do was feasible. He said not only was it feasible but quite easy. In addition he said you would be able to turn it on or off at any time even while the car was in motion. So with diagram in hand and an on off switch from an old set of driving lights I went to work.
First you remove the housing around the steering wheel column that sits directly over the center of the wheel. This will expose two screws on either side of the steering column that secures the underside of the dash cover below the steering wheel. Next remove the under the steering column dash cover by removing the two screws listed above plus two lower screws on either side. One is below the fuse box and the other is below and next to the center console housing. The fifth and final screw to remove is located on the right side of the fuse box through an access hole in the fuse box.
Remove the dash housing locate the single black wire that feeds into the back of relay 605. Cut that wire in half making sure that you leave the ends long enough to work with OR BETTER YET use a wire tap and then cut the wire in half avoiding having to make a splice. Then connect a longer (aprox 18") to the half that is receiving power and then connect another 18" wire to the other half that leads into the back of the relay. Next finish by connecting those two wires to your on/off switch. You may want to take the new power wire and hook that to the on side of your switch. Use the remaining black wire coming out of the back of relay 605 and hook that to the off side of the switch. This wires the switch so that in the on position power is boosted. If you reverse the switch connectors then in the on position steering is not boosted. You should do it which ever way makes sense for you.
Lastly install the switch any place you want. If you do not wish to cut the dash you may want to install it in the owners manual space under the steering column. Make sure you test all your connections before putting everything back together.
The result is...when the switch is engaged you have steering boost. When it is off you have no boost and tighter steering. I made this modification on September 30, 2000 and have had no problems at all. You are even able to engage the boost and un-engage the boost while driving with no ill affect. Good luck and if you have any questions please feel free to e-mail me.