Woke up this morning to find my tail lamps stuck on. They were definitely off when I locked the garage up last night. I started the car and switched the lights on and off. Shut the car and tried locking. Tail lights still stuck on. Everything seems to work like normal, except the tail lamps are stuck on. Since I was heading into work, I elected to take the other car until I could dig into the electrical diagrams. I put a charger on it to keep the battery from going flat, but I'll have to sort this out when I get home. Has anyone else seen this issue in the past?

 

When I get home I think I'll check relay #3 in the trunk fuse block. At least that way I can determine if the Body Processor Module is requesting lights or if the problem lies further down stream. This car makes me laugh every time it lives up to its reputation.

 

It's the tail lights and not the brake lights, right ? Relay or BPM sound logical.

 

Just tail lights and rear side markers. No brake lights, fog lights, or reverse lights. I didn't check the license plate lights, but I assume they are also on.

 

Bad news. It looks like Relay 3 in the trunk fuse block is getting a command from the body processing module to turn on. Need to figure out what to look at next. Any suggestions?

 

Bear in mind that the BPM signal is an active low, so you could have a short on the red/blue wire between the BPM & the relay.

Or, possibly the relay contacts have stuck together? You can swop with the stop lamp relay (5) to check. Pretty sure they're the same.

 

Thanks Michaelh. The relay is not stuck, swapped it. Control line from BCM is pulling low, could be a short somewhere. I tried a full hard reset and it came back up with the lights on. I guess next step will be to disconnect the bpm and see if I still have the control line pulled low. What's the interchangeability on the bpm's?

 

VCATS!!!!!!!!!!!!!!!!!!!!

bob

 

VCATS label says LJB2500AF/163; so it sounds like any LJB2500AF from a convertible should work right? Any programming required?

 

If I swap the BPM, will I need to put a code in for the radio? I've had the battery disconnected for hours at a time and have not had an issue with the radio code. I have no code card in my owners manual.

 

Most of the US cars aren't coded so you're likely OK - particularly if you've had no issue when disconnecting the battery previously.

You could just pull the plug on the BPM (disconnect battery first) and check for a wiring short. It's pin 95 on the connector to the BPM (FC14). There's another Red/Blue wire on pin 7 so make sure you get the right one.

M

 

Thanks michaelh
I may just do that. From the schematics, it looks like that wire only goes between the BPM and the tail lamp relay, so with the relay and BPM disconnected the wire should show very high resistance to chassis. Do you know of any particular trouble spots where that wire can short? I went ahead and ordered a BPM on ebay; seems to be the right part number and it's from a convertible. I'll check the wiring before I throw the new module in. Price wasn't bad and it sounds like it might be a good part to have on hand.

 

Just did some late night measurements in the garage. With the battery disconnected, the BPM disconnected and relay removed I was still measuring 115 ohms between the relay control pin and chassis. I reinstalled the relay and reconnected the battery. The running lamps in the rear were still on even without the BPM connected. I think I may have a short to chassis in my harness between the BPM and trunk fuse block as michaelh has suggested, so a new BCM won't help that issue. I wish it was a BCM issue because I have no idea where to look for a short and its probably buried in a hard to reach place.

 

I've convinced myself that this is not a BPM issue. I poked around to find a short but had no success. I yanked and pulled on the harnesses and couldn't get the tail lights to flicker. Wherever that 115 ohms is coming from it's pretty consistent and draws enough current to activate the relay for the tail lamps. For now I've jumper-ed a spare relay on pigtails to the unused aux relay port in the trunk fuse block. At least my tail lights now come on with the key instead of all the time. The weather is good, I'll keep enjoying the car. Finding the short might be a project for winter.

 

Odd one. I've re-checked JTIS and there should be nothing hanging on that line between the BPM & the trunk fusebox.

It does pass through two connectors on its travels so you could adopt a 'divide & conquer' approach:

BT2-9
BT2 20-WAY MULTILOCK 070 / WHITE TRUNK / ABOVE RIGHT HAND REAR WHEEL
which might be a pain to get to on the convertible and

RH2-16
RH2 20-WAY MULTILOCK 070 / WHITE REAR OF CENTER CONSOLE ASSEMBLY
which I think you can get to by removing the tray under the console lid.

Nice job on the relay patching, BTW.

 

Does your car have a Lamp Control Module, as per the earlier cars?

 

There is a lamp control module, but it is downstream of the relay. As far as I can tell from the schematics, it looks like the lamp control module only monitors the lamps to check for a bulb failure.

 

I had this problem with my 96 XJ6. I had a specialist track the problem down, he found that the drivers seat module had a short in it and this was indeed the problem. This required a new seat module, but it was worth it.

 

Having a similar problem to Nerobergstr ! ? Measuring 8 volts at the brake lights and shift lever solenoid, activating neither. Also assuming a short with no luck at finding a solution (yet).