About 90% of the time that I drive my XJS, I have no electrical problems and everything works as expected.

The other 10% of the time, the following won't work upon start up, but then they begin working all at once, sometime after a few seconds, sometimes after 15 minutes or somewhere in between:

Turn signals, radio, hvac (no action from fans on any speed), electric windows.

While those items are not working, the following still work and have never gone out: all gauges, electric seats, interior lights, headlights, trip computer.

As of my latest drive, the same problem occurred and the trouble items did not start working even after 30 minute drive (Turn signals, radio, hvac (no action from fans on any speed), electric windows.)

The trouble items don't share a common relay or fuse. I'll start going over the particular fuses and relays to look for issues, but do these symptoms point to any particular harness, or some area I should focus on? Any input appreciated.

 

I've three ideas:


1. Battery cables, at the battery and at the firewall post and the chassis ground.


2. The ground strap under the car from chassis to transmission.


3. The ignition switch and it's connector. Heavy key rings take a toll on the guts of these sorta pun switches. How do I know, guess...
Carl

 

They are different harnesses but the common denominator is their location under and/or around the HVAC or more to the point the heater core.

My guess is a leaking core (or O rings) has deposited coolant in the connectors. To investigate this remove the side panels at the front of the centre console and have a look for signs of coolant on the harnesses. If there are signs I would suggest removing the console and you will need to replace the connectors.

Let us know how you get on if this is the issue I can give you a headsup on the type of connectors I used.

 

Warrjon and CadJag, thanks for the suggestions.

I removed the console cheek panels and couldn't see any evidence that there have been coolant leaks, any deposits, or anything clearly out of order. Pretty clean and a little dusty. I examined the battery terminals and the battery posts on the firewall. All look good, clean and secure. The battery posts on the firewall still have the rubber protective boots in place. I haven't gotten under the car yet to check the ground straps, but will do so this weekend.

I checked the fuses of most of the specific items that are not working and tried replacing them with new fuses. No change. These are atc blade type fuses rather than the typical glass barrel fuses.

The following items work fine: all gauges, headlights, fog lights, starter, interior lights, tail lights, the convertible top and rear quarter windows, electric seats, power mirrors, horn, wipers, power locks.

The following items do not work: turn signals, brake lights, radio, electric windows, the electric fan. hvac (nothing happens on any setting and the compressor does not kick on).

In addition to checking ground straps I'll plan to check the rest of the fuses that I haven't checked yet, and I'll spend some time looking at the electrical wiring diagrams to see if perhaps there is a common harness in play here.

I keep the car parked in a garage. I typically disconnect the battery between uses since there is no outlet for a battery tender in the garage, and it can sometimes be 2 weeks between uses. Does the ECU control the electrical system in addition to engine management, such that constantly disconnecting the battery could cause the ECU to act up?

Thanks again for any input.

 

Well after reviewing the electrical guide it looks like several of the non-working components are fed through the auxiliary ignition load relay. I'll take a look at that when I have the chance and report back.

 

YEah I chased an electrical issue with my 89 for almost 1/2 a day before I found the culprit blown fuse. All the electrical diagrams and ROM said the fuse I was looking for was in the auxiliary fuse box under on the passenger side, it was the Owners manual that pointed me in the right place for the fuse, completely different location in my car.

So the moral of the story is - Jaguar modified stuff that is not in the ROM

 

I had problems with my 89 due to what turned out to be a minor leak in windshield. It had caused several of the spade connectors in the fuse block to not have good connection, and would act weird. It took some searching to isolate out, but once I did, it was very evident what the problem was.

 

Try cleaning all ground points, fuse connectors and plugs. I did that with my 89 and everything worked after.
Disconnect battery and grab some emery cloth and a can of contact cleaner and go for it. I takes a few hours but well worth the time

 

This leads to an important point that, like the harness, multiple circuits that aren't involved with one another can still share large connectors.A 12 pin connector could be several different circuits that aren't necessarily related to one another. I don't know where to look in particular, but even dirty terminal or a common ground is worth investigating given the amount of shared connections.

Also maybe check your battery/connections and voltage regulator. Different parts behave differently, I can have a low battery and the windows will operate normally, but the gauges will fly all over the place.

 

Thanks for all the input gentlemen, I think I have it resolved. It appears it was the auxiliary ignition load relay. I swapped it out with the adjacent seat heater relay and the windows, hvac, turn signals, brake lights, aux fan all work again. I'll pick up a couple new relays this weekend.

The only thing that still didn't work was the radio. I'm thinking one of the other fuses to the radio is the culprit. When I get some time early next week I'll examine those and I'll also post up some photos and details of the relay issue to help anyone else that may get this issue.

Thanks again.

 

Glad you got it fixed................