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1992 Ls400 Shifting Problems


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I have a 1992 LS400 that started having a strange problem where the R(everse) Light on the dash comes and the other dash lights dim when I press the brake pedal. Even when the car is not running, I press the brake pedal and the R(everse) light comes on. I have also noticed that the car shifts erratically and when I press the brake at driving speeds, the car seems to downshift.

All these symptoms started to happened at once.

Any ideas?

John Hoffman

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  • 2 weeks later...

Hey Hoffmnjp

Im about a week late on your post I dont know if you have fixed it yet but if not heres your fix.

You do have a bad ground.

Very common in early LS's.

Open the trunk on the drivers side trunk hinge (curved bar attaching trunk to car)there is a black plastic piece running the length of the hinge protecting a small wiring harness that runs through the trunk hinge.

Pull that down and out of the way.Pull the harness out of the hinge it kind of runs down the hinge and then goes up and makes a u turn pull that out .You can pulldown the trunk liner on drivers side and see where it snaps on to a bolt pull that off of the bolt to give yourself a little more wire length to work with.

Now you will see where the wires make a uturn inside another plastic piece.Unravel the tape in this area and remove the plastic piece.

You will find a broken wire (white with black stripe) made a little to short at the factory.

Splice in a small 2 inch extension betweeen the broken ends preferably solder it ( use butt connectors that you crimp on or twist and tape if you must.)

Tape the harness back up.

Put it all back together.

And your problems will disappear.

Hope this helps

Post back and let me know how you did


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  • 1 month later...

Wow! Yesterday (July 5) in 100+ degree Kansas City weather, my 90 LS400 started exhibiting this exact same problem with the "R" (reverse) dash light coming on whenever I pressed the brake pedal while the shift level was in "D" (drive) and with irregular shifts between gears.

And for the past three years or so, the "light out" indicator in the instrument cluster had frequently illuminated even thought no exterior lights were out. My local non-dealer repair shop tried several times to trouble shoot to no avail.

The solution from Lextek was exactly correct. This morning I found that, while the insulation for the "white with black stripe" ground wire was still intact, it was obvious that the wire core had broken at the point where the wire makes that 360 degree turn in the trunk lid hinge. What a quick fix for a nagging problem!

Thanks for the help!!! We still love this car after 13 years of ownership.

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I had the same problem a week ago.The info. provided here is whaat my dealer told me after I paid 272.50 for the labor and a little wire.I wish I knew about this site a week ago.Oh well. I have a problem I would like some help with if possible. My check engine light keeps coming on.The dealer said it was a "code 21 or 25" What is that? How much will it cost? Also my lights on my clock and radio display are burnt out. Any help for me and my 1992 LS400?

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