Hello Gentlemen:

I'm trying to determine why my 3rd brake light isn't working.

After checking the obvious (bulbs) first, I next checked the fuse. Bulbs and fuse are OK.

Next, I pulled the fuse and checked to see if the fuse itself was getting power by inserting the tester into the empty fuse slot.

No power in that slot.

Is this likely simply a short in the wire that carries current to this fuse slot?

Could someone please tell me how to proceed? I'm sort of stuck.

Thanks so much. You guys are the best, and have been absolutely invaluable to me in helping to get this car in shape. (In fact, the "renovation" is nearly complete.)

SirJag

 

SirJag:
The fuse in question isonly powered when the brake light is on. So, if you tested it when the brake pedal is pushed, then the most likely culprit is the brake relay. I cannot read the number on the print I have in front of me, but if someone else does not ID the relay before then, I can look tonight.

 

Thanks for your assistance.

Yes, I did test when pushed. Is the 3rd brake light on a different relay, because my other brake lights DO work.

Thanks for all your help!

SirJag

 

The 3rd brake light (called High-Mounted Stop Lamp in the wiring diagram) is provided 12V from fuse #8 (10A) in the trunk fuse box. This fuse is fed 12V from the Stop Lamp Relay - relay #5 in the trunk fuse box. The rest of the stop lamps are driven by the Security and Body Processor modules, so this relay, controlled directly by the brake switch, is only for the 3rd light.

Refer to Figure 09.2 in the diagram here: http://www.captainjaguarscathouse.co...ec%20Guide.pdf

The relay gets it's power from the Battery Power Bus - shown by 1 inside a square in figure 01.1 - so if this power was missing, many other things would fail too.

Since the fuse is good (as you described) and the power bus is good (else you'd have a lot of other issues) and the brake switch is good (else the other brake lights would not work), since you see no 12V supply at the fuse when the brake pedal is pushed (BTW, key must be in run position also) it certainly sounds like the relay is at fault.

 

Quads got that spot on.

 

Hi SirJag
I found this Boot(Trunk) Fuse Box Relays Diagram. Look at Relay #5 (Stop Lamps -HMSL and trailer only. HMSL means High Mount Stop Lamp (I think).



I looked at these relays in fuse box located in the Boot (trunk) of our Jag. Part number is LJA6703AA.
It has been superceded by part number C2P11192.
Gaudin Jaguar Parts has it for $4.63 plus shipping of $12.95, total of $17.58.
Rock Auto Parts total is $14.22.

Maybe you should try switching the High mount stop light relay (#5) with the side marker (#3). That will tell you if the relay is good or bad.

I hope this helps.

Jim Lombardi

 

Talk about a thorough and logical deductive sequence. Thanks so much. I will check that relay. Funny, but it seems the last owner was stumped over this. The brake light was off the window... seems like his mechanic couldn't figure it out. Thanks to you and the other great contributors to this forum, I sound like I know what I'm talking about now.

Thanks again...

SirJag

 

Perfect Jim... THANKS! I was looking at the relays yesterday and wasn't sure which was which. This will help! Also, thanks for the shopping leads... couldn't ask for more from my fellow Jag friends here in this forum. You guys are the greatest.

<HANDSHAKE>
SirJag

 

You are most welcome. Believe it or not, it's what I do for a living - I'm a consulting Electrical Engineer that's brought in to troubleshoot tough problems in complex systems that have, so far, stumped the engineering staff... the Jag electrics (at least those that have accessible information) are a walk in the park, in comparison.

 

Hi Quad,

Is your specialty quads as your name suggests... or are quads just your hobby?

SirJag

 

Hobby - I have four quads, three scooters, two bikes and my Can-Am Spyder which doesn't really have a definition - sort of tryke... The name comes from raptorforum.com, where I'm the electrical guru - I know the Yamaha Raptor 660's electrical system like the back of my hand.

 

what mechanical makeover are you into?

 

Wow: responding to an eight year old thread. I haven't seen Quad on this forum in years.