Brake lights come on when accelerating.

Joined
Sep 1, 2021
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41
Location
Coldwater, MS, USA
Brake lights come on when accelerating.
Actual lights not the dash light.

('97 lx450 is still running rough after:
New ignition coil, plugs, distributor cap, rotor, and new injectors.

Injectors test out all the way to the ecu.

Wiring harness by the egr has been inspected, cleaned, and heat taped))

Now the brake lights are coming on when accelerating. They do not go off until the brake pedal is applied and the regular circuit is activated.

Do I have an electrical short somewhere?

Has anyone else encounter this?
Thanks
 
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Joined
Sep 1, 2021
Messages
41
Location
Coldwater, MS, USA
Return spring seems fine.
I did an oem Brake Booster replacement 1 month ago.
Stupid and unlikely question,but could the vacuum be pulling the ppeda pedal enough to engage the switch under acceleration?
 
Last edited:
Joined
Sep 1, 2021
Messages
41
Location
Coldwater, MS, USA
I was thinking the ECU was bad since all of the ignition components have been replaced and it is still misfiring.
Then I noticed the brake lights coming on.
So I guess I should hunt down this Gremlin before I buy a new ECU.
 
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Dec 24, 2019
Messages
352
Location
Sydney, Australia
The first step for this should be to examine the electrical wiring diagram to see what components are involved. If you don't already have it, you can download the EWD for a 97 LX450 from the resources section in MUD:

From that manual, here's the diagram of the circuit driving the brake lights:
1631366128301.png


As you can see from this, unless you have a short, the only way you should be getting the brake lights illuminating is by the stop light switch going closed circuit, which it does when you press the pedal. I would definitely focus there as being the most likely issue.

The stop light switch itself could be faulty, or it could be adjusted incorrectly. I'd get up there and have a good look at it. Try toggling it with your finger, make sure it seems to be working correctly. Check to make sure the switch is being depressed well by the pedal when it goes fully up. The switch is adjustable, it's on a screw thread, so if it's only barely pressing on the switch with the brake pedal fully up, you might need to physically adjust the switch and move it closer to the pedal to make better contact. I'd wager your problem lies here.

Now, if your problem is with shorted wiring, and the switch is working correctly, that would mean your lights are getting +12v through some other connection than the brake switch. Easy way to test that - unplug the brake switch. If your brake lights stop working completely, even under acceleration when you've noted them going on by themselves, the problem isn't shorted wiring downstream of the switch, it's the switch not doing its job properly. Problems with any kind of shorting before the brake switch wouldn't cause the issue you're seeing if the brake switch is working and adjusted correctly.
 
Joined
Sep 1, 2021
Messages
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Location
Coldwater, MS, USA
Pedal height adjustment was the Gremlin.
Thanks.

Also the rough running is solved this AM.
Injector wire was arcing to the valve cover.
I discovered it after I unwrapped the wires further down from the EGR.

Thanks for all the Mud help on that.
 

Azca

If there is a harder way - I will find it...
Joined
Oct 25, 2007
Messages
1,511
Location
Surprise AZ.
Pedal height adjustment was the Gremlin.
Thanks.

Also the rough running is solved this AM.
Injector wire was arcing to the valve cover.
I discovered it after I unwrapped the wires further down from the EGR.

Thanks for all the Mud help on that.
This is very common with these rigs. Fix the short and wrap the entire harness in that area with heat insulating tape or wrap. Wrapping the EGR pipe will also help. They make a split loom type of insulator that I used for this purpose.
 
Joined
Sep 1, 2021
Messages
41
Location
Coldwater, MS, USA
This is very common with these rigs. Fix the short and wrap the entire harness in that area with heat insulating tape or wrap. Wrapping the EGR pipe will also help. They make a split loom type of insulator that I used for this purpose.
I used 2000° tape.
 

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