On the IS350, if your headlights are on, and you use the windshield washers, the headlamp washers will automatically activate... I didn't like this... There is a separate button for the headlamp washers that activates the washers so why would you want them to go on automatically if you just want to clean a small smudge on your windshield?
Anyway, with the help of Lance (aka the Toyota/Lexus master) I was able to disconnect the two systems so they are now totally independent... They key is to prevent the signal from the windshield washer from ever getting to the headlamp washer... This is done at the main engine fuse/relay box under the hood... It's located on the drivers side near the front of the car... The wire in question is under the Front Connector Block, Connector 2F, PIN 8... It is an orange/blue striped wire with silver paint markings... I used a tiny 1.5mm flat head jewelers screwdriver to release the wire from the connector... You can then use heat shrink or electrical tape to tape up the end of the wire and tuck it away... Alternatively, if you want, you can just cut this wire and be done with it... But, I decided that when I get rid of the car, I wanted to re-enable this feature so at that time I can just remove the tape/heat shrink and stick the wire back into the connector...
Put things back together and you are done... I tested it afterwards and it works like a charm... The only time the headlamp washers will activate is when you press the headlamp washers button...
First Picture: This is the box, held in place by 3 clips shown... Simply press on the single clip near the front and pull the lid off...
Second Picture: Here is the box with the lid off... The Front Connector Block is shown, that is what we are going to remove... There are two clips on either side of it... Press both at the same time and pull it out...
Third Picture: This is the connector underneath the Front Connector Block that we are interested in... Unplug this...
Fourth Picture: The wire we are interested in is PIN 8, which is an orange/blue striped wire with silver paint markings...
Fifth Picture: Here is another view of the wire we want to disconnect...
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