Different Taillamp Failure Problem

[91LS400vgb]

My recently acquired 1991 LS400 taillamp failure indicator lights up (and stays lit) as soon as I apply the brakes the first time after startup. All 8 (the 6 1157's and the 2 high-mount 921's) brake lights appear to be working when I do not have the headlights (or parking lights) on. The six 1157 bulbs also light up when I turn on the headlights by themselves. However, when I have both the headlights and the brakes on at the same time, the rear upper left bulb does not light. I have tried several things, initially just replacing that one bulb, and eventually replacing all 8 brake bulbs. Nothing has worked. I checked inside the taillamp failure box and it looks fine. I once had a similar problem in my 1989 toyota camry and fixed it by replacing a non-factory rear bulb with a genuine toyota bulb. Tried that with my Lexus but it did not work. Anyone have a similar problem? The previous owner changed the battery out just before I purchased it. He also had the power steering rack and pump changed which makes me wonder if the alternator has anything to do with this. The car has 94k miles. Thank you for your help.

[LexInfo]

My recently acquired 1991 LS400 taillamp failure indicator lights up (and stays lit) as soon as I apply the brakes the first time after startup. All 8 (the 6 1157's and the 2 high-mount 921's) brake lights appear to be working when I do not have the headlights (or parking lights) on. The six 1157 bulbs also light up when I turn on the headlights by themselves. However, when I have both the headlights and the brakes on at the same time, the rear upper left bulb does not light. I have tried several things, initially just replacing that one bulb, and eventually replacing all 8 brake bulbs. Nothing has worked. I checked inside the taillamp failure box and it looks fine. I once had a similar problem in my 1989 toyota camry and fixed it by replacing a non-factory rear bulb with a genuine toyota bulb. Tried that with my Lexus but it did not work. Anyone have a similar problem? The previous owner changed the battery out just before I purchased it. He also had the power steering rack and pump changed which makes me wonder if the alternator has anything to do with this. The car has 94k miles. Thank you for your help.

The taillight warning circuit do have an input from the alternator. it receive the charging voltage from the alternator if i remember correctly not sure what exactly do, I had an early LS that did the same thing and the guy had an alternator from pepboys that was giving an idle charging voltage at slightly above 12.5 volts due to a faulty rectifier inside the alternator, replaced with an factory unit and the problem went away. you have to make sure your alternator output voltage is above 13.00 v at idle and take it from there.

hope this helps....

[Arkansawyer]

You will probably find a post by me that is exactly what you describe. I have the exact same symptoms that you list and have tried the exact same remedies, to no avail.

Got a factory alternator that I bought off of ebay coming in pretty soon. Hopefully this will indeed be the fix. Fingers crossed.

[CUMan]

A very common problem on the early LS models involves a broken wire in the wiring harness which is attached to the driver side trunk hinge. I have never heard of this problem causing the exact same thing that you are experiencing; however, it does cause numerous electrical problems which manifest themselves in strange ways. You can read the numerous posts about this problem by using the "Search" function.

The wire involved is white with a black stripe. It is a ground wire. Pull the wires loose from the trunk hinge, remove some of the tape around them, and look for this particular wire. The wire may be broken. If so, repair the break by splicing a short length of new wire into it. The problem apparently occurs because this particular wire is too short. The flexing as the trunk opens and closes eventually puts enough strain on the wire to break it.

Another possibility is that you have corrosion in the taillight socket. Clean all electrical contact points where the bulb mates with the socket. Another thing to try is bending the contacts at the bottom of the socket to make them fit tighter to the bulb.

[91LS400vgb]

Thanks for your advice everyone. I'll do some more investigating and let you know what I find.

[91LS400vgb]

Just a quick update to this - I finally got around to checking the trunk hinge wiring, as CUMan suggested. Unfortunately, I did not find any breaks in any of the wires (I even removed tape further below the hinge and did not find anything). I still have the same sympton, i.e., on my leftmost tail lamp, which has 2 bulbs, the upper bulb does not illuminate when I have both the brakes and headlights on at the same time. This is accompanied by the taillamp failure indicator on my dash. Otherwise everything is normal. The sockets all look good too. Perhaps it is related to the alternator as LexInfo suggested. Thanks for all your help on this, everyone.

[Arkansawyer]

Apologies that I never updated my results with replacing the alternator. As luck would have it the alternator did not cause the light to go away. It is my belief that since I replaced all the bulbs with non OEM it is causing this light. The electrical draw from the non OEM is different enough to trigger the light. My guess is that replacing bulbs with OEM will keep the light from coming on. Just a wild guess on my part.

[91LS400vgb]

No problem, Arkansawyer, and thanks for your post. Actually, one of the first things I tried was replacing all my bulbs with new ones I purchased from a Lexus dealer as that is what remedied an almost identical problem I once had with my 1989 Camry (see original post). However, it didn't fix it this time. Btw, my taillamp failure indicator usually only goes on (and stays on) when I press on the brakes the first time while the headlights are on. The failure light does not go on during the day (as the headlights are not on).

I think it's still a good idea for you to try replacing your bulbs with genuine toyota ones. Let me know how it turns out.

[Arkansawyer]

I think it's still a good idea for you to try replacing your bulbs with genuine toyota ones. Let me know how it turns out.

Honestly I probably won't go through the cost and time to replace every bulb with OEM as I had replaced every bulb with aftermarket and would have to change every single one. I'll just live with the light on the dash.

BTW, its good to be back on this board for a bit after a long stint away.

[teamer]

91LS400vgb, was your car ever in a previous accident? The reason I ask is because if it was, sometimes the electrical system may get damaged in the accident and it is very tough to diagnose where there may be a short.

Just a thought. I know your symptoms- I've seen other LS400s of that generation (my dad owns one) that have the same or similar problem. I've often wondered if it is simply a problem that comes with age of the car (electrical system deterioration - corrosion) or the vehicle was in an accident that damaged the electrical contacts.

Curious to find out...

No problem, Arkansawyer, and thanks for your post. Actually, one of the first things I tried was replacing all my bulbs with new ones I purchased from a Lexus dealer as that is what remedied an almost identical problem I once had with my 1989 Camry (see original post). However, it didn't fix it this time. Btw, my taillamp failure indicator usually only goes on (and stays on) when I press on the brakes the first time while the headlights are on. The failure light does not go on during the day (as the headlights are not on).

I think it's still a good idea for you to try replacing your bulbs with genuine toyota ones. Let me know how it turns out.

[91LS400vgb]

Wow. Actually, the previous owner was in a minor accident and he had the driver's side front fender replaced as a result. I wonder if that's the reason. Hmm, something for me to think about, but still seems odd that it wouldn't cause any other problems. Thanks teamer.

[LScott400]

Something we ran into on our '94 was a couple of the brake light lamps wouldn't activate when the pedal was depressed. In checking the sockets we discovered the contact nubs were worn. Adding solder to the bulb contacts corrected.

[91LS400vgb]

I think my case is different because the bulb will light if the brakes are applied without the headlights, or the headlights are turned on without the brakes. It just doesn't light when both brake and headlights are on at the same time. Therefore, I would think it's not a contact issue, but I'll recheck the socket anyway. Thanks for the info, LScott.

[91LS400vgb]

Just an update - after replacing my failing battery with a brand new one, the condition I described above only occurs occasionally. The lights now function normally (with the rear lamp failure indicator off) most of the time.

[scottelble]

Just an update - after replacing my failing battery with a brand new one, the condition I described above only occurs occasionally. The lights now function normally (with the rear lamp failure indicator off) most of the time.

I too had this problem a little while back...I used non oem lights but that wasn't the problem. What it ended up being was the light i used was not the same voltage amount so even though the bulb was working the voltage was too small for the breaklight failure light to recognize the it indeed was working...After using a bulb of the same recomended voltage the problem was solved:)