The bulb failure light on my 1990 XJ40 is acting weirdly. With the car sitting still, it stays off. When I am driving down the road, it will flash on and off with no definite pattern. It sounds like it could be a bad connection or loose bulb, but all exterior light bulbs are working. Any thoughts on how I can track down the problem bulb?

 

Most likely you do not have a problem bulb, but a faulty bulb fail module.

These are known to go bad and most of us just live with the bulb fail light permanently illuminated.

Mine has been lit for 8 years now.

Although there is a good write up in the XJ40 book about rebuilding them. IIRC

 

Robert:
Yes, BFM's are notoriously weak on this car. Many of us live with permanent or intermittent faults. Presently, mine is off! You may simply want to go over the car bulb by bulb to make sure they are firmly seated. Otherwise, I'm afraid it is a process of elimination at figuring out which has gone bad. Lots of write-ups in the forums archives to begin your search. Still, of all the fault lights that could go on, this is the best one to have!
Cheers and good luck.
Scott

 

Hi Robert,

Richard did make a good point about reading the 2 bodges and reflowing the Lamp Module circuit boards described in the XJ40 Book.

I agree with Scott in that it's going to be a "process of elimination".

I'm going to make two suggestions.

1. If you don't have a Haynes, please buy one.
2. The following circuit I "pulled" from Haynes.

There are four Relay and Bulb Failure Modules (RaBFM). From each one there is a PNK/GRY wire that leads from and connects to the dashboard Hazard Display. I've highlighted them in Fuschia.

So, I would disconnect the PNK/GRY wire from each of the RaBFM boxes and see if that stops the flickering dash light.

1. If it does not stop the flickering dash light, then the problem is somewhere else.
2. If it does then it's just a matter of reconnecting each box until the flickering returns. That box and associated circuitry is where you spend your time troubleshooting. You may even want to do the solder reflow found in the XJ40 Book on that box.

Good Luck

 

It might also be a loose ground,my 90 would show warning with all lights working then when driving in the rain warning light would go out. Tightened all the grounds and seems to have cured the problem.

 

Thanks, all, for the good feedback. Now allow me to through another variable into the equation. Last night, I took a round-trip drive of about 2 hours duration. During the entire trip, the bulb failure light flickered on and off. This morning, as I pulled away from the house to take my daughter to school, the light started to flicker again, but as I drove into a heavy downpour, it stopped. It didn't come on again all day while rain was falling intermittently, but once the rain stopped and it dried up, the light started flickering again. Does this cancel out any of the suggested fixes?

 

Exactly the opposite. It points directly at one of the posted fixes.

 

When driving in the rain the grounds got soaked and made contact,thus the failure light going out. The most likely bulbs that are not grouning are the side marker lights,(check them by having someone watching the dash and tap the side marker lights,or take a hose snd spray water on them from underneith the bumper areas).