my 92 d350 brake lights stay on, on the dash. My brakes are spongy and don't get anything till it is almost to the end of the pedal. I've changed my master cylinder. Could it be the booster? i need some advice.
Rear brakes could be out of adjustment. For a quick test set the EMG brake. Then see if the pedal firms up. If it does repair the self adjusters. If it does not bypass the the RWAL valve it is bad most likely.
The light on the dash means the anti lock brake system sees a problem or the vacuum system isn't working properly. Yuur not complaining of a hard brake pedal so I would rule the vac system out.
Most of use unhook that RWAL system controller. It wasn't a good system new and it didn't improve with age eather.
I had the same problem and replaced the MC and booster with a rebuilt one. Problem gone for about 6 months then came back. replaced again with a new MC and all has been fine for about 4 years.
2 brake lights, one is proportioning and one is RWAL. If it is the proportional, an adjustment of the rear and good bleeding may be in order. Then reset the switch per the manual.
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