Next problem that needs fixing are the dome lights. They're always on. The buttons on stereo panel don't do anything. Where should I start looking for the problem?

 

Hi danpop,

You can download the 1991 XJ Electrical Guide here:

http://www.jagrepair.com/images/Elec...Electrical.pdf

The Interior Lighting schematic is shown in Figure 9 on page 27 of the pdf file. The source of battery power for the lamps is shown in Figure 1 on page 11.

Looking at Figure 9, battery power is always available to the dome lamps via the Brown wire with a White tracer stripe (NW is the color code - see the color code chart on Page 3 of the pdf). The continuation of this wire is linked to Figure 1 via the page-jump link (the number 71 in a square box).

In Figure 1, you can see that link number 71 connects to Fuse C2 (7.5A) in the right fuse box (which is at the base of the right A-pillar).

Back at Figure 9, you can see that another wire from the dome lamp assembly, which is Red with a Light Green tracer stripe (RLG), connects directly to the Central Microprocessor, or CPU. Since the lamps always have battery power available, we can conclude that the CPU turns the lamps on by connecting them to ground, and turns them off by disconnecting them from ground. The RLG wire appears to be the path by which the CPU automatically grounds the dome lamps when the doors are opened.

The third wire is Slate with a Blue tracer stripe (SU) and connects the dome lamps to the Center Console Switches, then on to the CPU via the Slate/Black wire (SK). This allows you to turn the dome lamps on manually via this alternate ground path.

So my first suspicion is that there is a short to ground, either at the lamp itself, somewhere in either the RLG or SU wire, or at the CPU connector or inside the CPU.

Since it's easy to drop the roof console, that's where I would start. Use a quarter to carefully turn the slotted plastic rivet 90 degrees and carefully work the console downward and slightly rearward. I used the word carefully twice in the previous sentence because the plastic parts become brittle with age. Look at the lamp for signs that one of its metal terminals has been touching a ground, or for a problem with the wiring.

If all seems well at the lamps, my next suspicion would be corrosion of the connector pins at the CPU due to the water ingress. There are two drains that run from the A/C evaporator in the Climate Control Unit in the center console down the sides of the transmission tunnel and out the bottom of the car. When (not if) the drains become clogged, water condenses on the evaporator and pools on a ledge in the CCU, then spills out onto the CPU while cornering. Search the forum for methods for cleaning the drains to prevent this from happening. The primary suspect here would be corrosion that has bridged/shorted the RLG wire to another connector pin that is grounded.

Getting at the CPU is not difficult, but it's a little time consuming because a number of things have to be removed or disconnected. The photo albums at the links below will give you an idea of what's involved. The first two albums show how to remove the passenger side knee bolster and glove box. The third album shows the electrical components (these photos are of our '93 which is probably a little different than your '91). Photo 5 shows how the CPU is mounted behind other electrical components that you need to move out of the way in order to access the CPU to check its connectors.

Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page

If there are no obvious issues at the CPU, you can check the RLG and SK wires at the CPU connectors for a short to ground, which could indicate that the short is in the wiring somewhere between the CPU and lamp. Hopefully you'll find an obvious problem at the lamps so you don't have to look any further.

Cheers,

Don