Help! No tail lights or sidemarkers

I was replacing the rt. rear sidemarker, now I have no tail lights either side. Brake lights and turnsignals work. Must be a fuse. Can't find it.

Uh...what kind of "cat"

XJ6 seriesIII 1985. Sorry about that

I still think it's a fuse because they were working one minute and not the next. Everything is well chassis grounded. There is no current to the tail and marker lights which are on the same circuit (rear and front? Same circuit? My manual is not clear on this point. Thanks for any input/assistance.

Not a Jag expert ,in fact I know "Nuthing"
But I would trace that wire back until you find current, a fuse , or a short

Have you found all the fuse box locations. Under dash driver's side, under glove box, under bonnet? Series 1 had them behind dash (speedo/tach ) under dash, under bonnet. Series 2 under dash, under glove box, under bonnet. Not exactly remember series 3, under dash under glove box or side foot panels on dr or pass, and under bonnet. Check how bulb was installed, if upside down ( yes it can happen ) can blow fuses. CD manuals can be had for less than $25 on sale.

I think it may involve the bulb fail indicator panel in the trunk. I checked all fuses everywhere else. The left tail light came back on so we are down to the rt. side. These cars have complicated elec. system. (Understatement).

Never heard of a bulb failure indicator on a series 3. have them on the AJ40s on each corner, unplug and clean connections or take apart the unit unplug chip, clean and replace. Pics of car would help memory.

There is a bulb fail indicator light on the dash and on the back wall of the boot.

According to Jaguar you have a bulb check unit # DAC 1562, Lamp failure switch ( up to chassis #301854) # C42984. (chassis # 301855 and up ) DAC 1908 and lamp failure transmitter C42291. The lamp failure indicators in boot, should be 3. According to Haynes they work by monitoring the balance of current drawn by paired bulbs. Fitting unmatched wattage bulbs or makes of bulbs can cause false alarms. A bulb failure unit cannot be repaired and must be replaced. The DAC1908 failure switches may cross to another # as they resemble the older series 2 instrument voltage stabilizers. If they cross to the stabilizer # C27503 you might find the Ford instrument voltage stabilizers cheaper. I assume you have a later model series 3 with fuel injection which would be chassis 301855 and up. Finally went to library and looked this up in 2 books. A British Auto/USA catalogue from 1/22/91, and Haynes Jag XJ6 68-86 series 1,2 and 3 from 1987

I have checked everything. There is no current to rt. tail light and no current to either rear side marker lamp. I have traced it back to the what I believe is the bulb fail. unit on the rear boot wall. All terminals are hot except the 1. Has the unit failed? Can it be bypassed? I am looking at the wiring diagram in the haynes guide.

Need to test more. Will consider a bypass, which would be straight forward.

Try a bypass, then switch one of the three switches and see which one does not work.

It was the bulb indicator unit. I bypassed it and now have my tail light and side markers working. Now just have to fix the rt front side marker and parking light.

All lights now working! There are 2 bulb fail. units to the right of the aux. fuse box and three in the boot. Now I know.