My XJR died suddenly yesterday not far from home. I had it brought home by rollback. It's an electrical problem. The battery was totally dead. I removed it and charged it OK. Reinstalled, it shows a > 30 amp short somewhere. My multitester only goes to 10 amps, so I have been blowing 30 amp AGC fuses while looking for the short. I removed all the 40 amp relays in all the locations I could find. No luck so far. I suspected a bad alternator but someone in the forum said that would not cause this. Has anyone had a similar experience or have any suggestions?

 

Welcome to the forum GyroGearloose,

I've moved your question from your Intro thread. Members here with the same model will be able to help.

Graham

 

Check the bulkhead connector?

 

Bulkhead connector or the alternator diodes. Separate the circuits using the bulkhead connectors and the alternator connector. Start connecting them backuntil you see the spark!

 

His handle here uniquely qualifies him to give this advice

Spark and ZAP!

 

instead of blowing up fuses, use a test light or incandescent bulb until things get narrowed down

 

Yeah, I didn't notice he was blowing fuses! So Gyro, is one of the car's fuses blowing or are you using an added fuse link for testing?

Do you have the schematic (look to the stickeys) and have you looked at the power distribution schematic? Actually, with the various fuse boxes, the X-308 is pretty easy to isolate a problem like this.

Do you know what we mean be "bulkehead" connectors? Actually, they are properly called "false bulkhead connectors" on the X-308 and they are the main power cables that terminate near the firewall.

BTW, I am GUESSING you have a shorted alternator diode.
Good luck.

 

Take the alternator out of the loop, replace the blown fuses, and go at it with the test light. The alternator diode is the biggest suspect, but it might be something else. A simple test light will sufice.

 

Thanks for the great advice - Sparkenzap, I'm not blowing fuses in the car but have a test probe with a fuse holder in-line. I've been taking out all the relays in a fuse compartment and then (with battery + connected) bridging from the battery negative post to ground with the probe and it blows the fuse ( 4 fuses so far ). So today I will try to take the alternator out of line and see what happens. Thanks for the test light advice. I bought a few boxes of fuses for this diagnosis. My idea was if it blows a 10 amp fuse but not a 20 amp then that would help me isolate the problem but so far it's blown all the 30s. If I disconnect the bulkhead connector and that eliminates the short does that mean the short is definitely in the alternator? Thanks again new friends.

 

Gyro:
No, not for sure, but you will at least resolve the problem to the front half of the car AND, the bulkhead connectors themselves are a potential short to ground. The have only a small platice insulator and if they have the common problem of getting loose, they will overheat and coul short to ground.

 

I disconnected the cable on the engine side of the bulkhead connector. The short is gone at the battery, but now blows the test fuse when I bridge the gap at the bulkhead connector with my test probe. Here's something else: When I ignore the short and hook up everything anyway the car will start but makes a new high pitched sound in the engine area. It sounds much like a power steering pump that's low on fluid. The pitch varies with engine RPM. Also get an electrical burning smell. Didn't leave it connected and running but a few seconds. Is this more evidence of a bad alternator. Thanks again for the help.

 

The car won't start with the cable disconnected at the bulkhead, but all other systems (radio, seats, windows, etc) work. If I can disconnect just the alternator somehow, should it start and run on the battery long enough for me to get it to the shop 10 miles away?

 

With a good battery you can go a lot further than that.

 

Yep, I'm with RJ. Just lift the big wire connected to the alternator (yeah, its a PITA to get to) and tape it.

 

Disconnected the big wire to the alternator (PITA, like you said). Bridged the gap at the bulkhead connector - no short. Started the car. Cancelled the rollback scheduled for Monday. Thank You All.