My 03 S-Type V8 Jag has very dim tailights and just a hint of a brake light on the rear passenger side. The third brakelight in the back window also flickers when you apply the brakes. However when I remove the brakelight bulb from the R.R. taillight assembly, the 3rd brakelight works fine. The drivers side is perfect. When I checked the voltage at the assembly, it only reads about 7 volts. The grounds at the rear fender seem ok. Any ideas what to check for?

 

explain what has 7 volts............ the brake wire has 7 volts?? or the main ground is showing 7 volts???

either way 7 volts is an issue

and i assume we checked for the correct bulb and base yes?

 

The bulb area doesn't have wires but is an assembly that you install the bulb into. The whole assembly then clips into the taillight lens. Hard to describe - like a printed circuit board only in solid metal. It holds all the rear pasenger side bulbs. I simply took a voltage reading at the circuit (also at the plug that connects the assembly to the wire harness) and only got about 6-7 volts. ???

 

Check the fuses by removing them and reinstall new if necessary.

 

If the fuse does not work, you need to trace back until you find 12 volts.

 

Yes and Yes... And also check both sides... The left and right are fused separately but also dependant of each other.. Meaning a short on one side can affect both... And like "phd12volt" stated... The correct bulbs are esential on these cars. Close doesn't work..

 

You have to be a bit circumspect with modern lighting on cars -- they are usually worked from a bus controlled by a microprocessor. If you find chips on the lampholder bases, that's what you have. Nontheless, look out for corrosion ANYWHERE, not just the lamp bases/sockets, this is a whitish powdery film. Look out also for "shorts" anywhere, symptoms being a little smoke as you look at the assy. while turned on, an unusual burnt blackness anywhere. Micros. may limit the current if there is a short to prevent a fire, but the micro. usually tells you somewhere there is an electrical fault.
Leedsman.

 

you need to check the indivual contacts for voltage. start with the ground lead (it connects the base) and measure that conection point to the main battery wire. you should see 12.6 roughly. If you do, then the ground is good. Now check the brake lead contact, with the brakes applied, and testing to the battery (-) lead, you should see roughly 12.6 if you do not, then you need to start tracing that back. (this is with the car not running, if it is running, you will see higher numbers due to the alternator charging)

 

Thanx to everyone who provided advice. Yessir!! Turned out to be just a blown fuse. About the last one (10amp) at the back of the box located in the trunk. I found it a bit hard to diagnose because there was still some power getting to the lights, but less than 12 volts which allowed the lights to glow very dimly ,not fully powered. I was convincing myself that it had something to do with the "rear electronic module", and that could have been a dealer repair item = $$$. Think I'll take my bride to dinner this eve.

 

Yes I know I went down that same road!

 

I had a similar problem and it was a blown fuse. In my case it was Fuse 53 in the rear fuse box in the trunk underneath where the spare tire is located. My right tail light was very faint and the middle brake light was weak and would flicker. Unusual behavior that you wouldn't expect from a blown fuse.

 

Just had the same issue cause an MOT fail in the old girl.
Garage reckoned it was the circuit board so I ordered one of eBay for a tenner, but after reading this post I checked the voltage across the circuit board and was only getting 4v.
I checked all circuits toake sure it wasn't the board then fuse 53 and it was toasted. New 10amp fuse and we are back in business!

Cheers