Interior Lights Dim When Brake Is Pressed.

[clacey]

I have a 91 LS400 when you step on the brake, the interior and dash lights dim a bit as if the electrical current isn't quite high enough. The alternator was changed a year ago.

Any input??

Thanks,

CL

[VBdenny]

Well C, something is causing a draw on your electrical system for it to do that. If your battery is 4 or more years older, don't even screw around, get a new one. When places test them, they always say they are okay, but remember, it is only a test. Kind of funny how when cars are running that the batteries always look good. I replace the batteries in all my vehicles every four years or at the first sign of what you described but that is sure what it looks like to me. I AM assuming that your terminals are all clean and free or nasty looking stuff. If your alternator was replaced by Lexus, I wouldn't worry, if it is an aftermarket, I'd have it tested. I have bought new aftermarket alternators before and not have them work properly. As a rule, I always have the parts dealer bench test my new alternator prior to leaving the store. I have seen 11.3v before on an "out of the box" unit. The guys said "uhh, well I dunno". I said get another one!

[90LS400Lexus]

Sounds like a weak battery.

[SKperformance]

do any strange lights on the dash also light up?

it might be the bad electrical ground located on the trunk arm .

The wires chafe and cause a short.

Also when you changed the alternator a year ago was it because your powersteering pump was leaking>?

If so then it may have destroyed yet another alternator.

[clacey]

Thanks for the replies.

The previous owner did say it was loosing some PS fluid but there are no visible leaks under the car. Could it be that the alternator is eating it? It is a very slow leak. If I replace the PS Pump, can I save the alternator or is it too late?

Thanks again.

CL

[90LS400Lexus]

If it is causing the odd light illumination- I would guess it is too late. I have not had the problem on my car, but from what I have read here- it is gone after that happens. I would look at the alternator and see if fluid has leaked in it. If not- I would guess that your battery is weak.

[clacey]

Does it leak externally where you can see it or internally? It's difficult to see anything in this car. Everything is so close together.

Thanks,

CL

[mjrav]

This "dimming" may be normal. Don't overreact and fix what isn't broke.

When you step on the brake it's normal for the engine to idle slightly slower resulting in slightly less alternator voltage. There may even be a flicker in the lights as this occurs. Mine always does - been working the same way for 140,000 miles.