Cluster goes dark and car shuts down

[RobBahre]

Car runs but as soon as I touch the brake my dash goes dark or it runs long enough to hit a bump and it dies, as if a wire short is happening, any ideas?   Battery and alternator are just fine. 

[RX400h]

It does describe a failing alternator when a high enough load causes the engine to die. Did you inspect the alternator connections? When the car dies, does it start right back up? When you step on the brakes do the brake lights illuminate?

[RobBahre]

18 minutes ago, RX400h said:

It does describe a failing alternator when a high enough load causes the engine to die. Did you inspect the alternator connections? When the car dies, does it start right back up? When you step on the brakes do the brake lights illuminate?

I had the alternator bench tested and it passed and reinstalled to be sure everything was correct cause I noticed the alternator flexing at the bracket.  When it first starts up it runs fine I can rev it up and all even start to drive if I shot from N to D or R, but as soon as I touch the brake or hit a small bump it shuts down and my dash goes dark sometimes it resets when I cycle the key off and on and sometimes it stays black until I unhook the battery and rehook it up, then it works fine again until I go to move it and touch the break

[RobBahre]

Update:.   I found one of the ground wires from the body to motor is broken off but I have no idea where it connects. 

[RX400h]

This is regarding a different Lexus but the response to the poster's question may be relevant to your situation.

Ground Wire attachment Location - ClubLexus - Lexus Forum Discussion

If not, hopefully someone with the same generation of RX300 can pop the hood and see where the ground wire is attached.

[RobBahre]

Ya I found one of grounds just hanging but can't find where it connects to.

[RobBahre]

7 minutes ago, RX400h said:

This is regarding a different Lexus but the response to the poster's question may be relevant to your situation.

Ground Wire attachment Location - ClubLexus - Lexus Forum Discussion

If not, hopefully someone with the same generation of RX300 can pop the hood and see where the ground wire is attached.

Unfortunately this is talking about the passenger side of the car with the alternator Wich has its own  body to motor grounding cable, one goes to back of the intake and the other next to the top coolant hose intake for the motor.     Definitely need a photo of someone else's set up. 

[RobBahre]

Found where the connection goes, it connects to a transmission to motor mounting bolt just to the right of below the starter!! Will update if this fixes dash board problems. 

[RobBahre]

On 8/29/2021 at 4:30 PM, RX400h said:

It does describe a failing alternator when a high enough load causes the engine to die. Did you inspect the alternator connections? When the car dies, does it start right back up? When you step on the brakes do the brake lights illuminate?

It ended up being a broken body to motor ground.  

[RobBahre]

Broken body to motor ground.  All good now. 

[RX400h]

Great news!