2000 S-Type Right Brake Light Issue

Hi. Looking for advice, or a tag to a similar post with the same issue.

2000 SType 4.0 US model

  1. “Right Brake Light” error on dash
  2. Bulb ok, fuse ok

Looking to get some advice on what to test next.

See attached image. On the left side, the brake light works and I measure 13.1 volts between the same 2 contact points.


The S type lights operate with a switched earth/common and the +13v will be measured on both sides of the bulb until the rear lighting control unit switches the earth at which point the bulb will illuminate.
All my past Jag’s had switched +ve.

The brake light and the tail lights on the right hand side share the same supply. It comes from fuse 7 (10A) in the Rear Power Distribution Box. If the tail lights on this side work, the supply to the lamp unit must be OK. If you don’t have volts where you should have, the problem is in the lamp unit, probably corrosion.

If you find you do have volts, as Neil says, the Rear Electronic Control Module supplies a ground to light the stop light when the brake pedal is pressed. It’s the black wire with the green tracer.