Hey all, I am experiencing an electrical gremlin on my '03 XJ8. At times, I can get into the car, turn the ignition to run and the dash will come to life for an instant and then go dark. There is a sort of hum coming from the dash and a relay cycling slowly. If I pull the key out and re-insert it, sometimes it will come back and be fine, other times it will take several repeats of this process and once in a great while I have to get under the hood and hook the battery charger to the front relay hot lead (this usually gets it running). There are times when it will do this at shut-down also and it doesn't seem to matter whether I shut all accessories off and allow the antenna to fully retract before shut-down or not.
(This includes manually tilting and retracting the steering and cycling the door locks open.) I have had the battery out of the car and load tested, and also had the tech do a starting test (of course the beasty wouldn't act up for the tech.) and all seems good with the charging system (13.95 volts with everything turned on) and never goes below 12.75 volts after shut-down. I know that all cars after about 2000 MY are very sensitive to system voltage and that modern electronics don't like low or erratic voltage transients and that these things can cause a whole raft of wierdness, but I have polished and tightened every hot and ground connection I can find. I suppose it could be a relay going bad, but which one to start with? Any recommendations from one or more of you electrical wizards would be greatly appreciated.

 

Juat a hunch- Check (for corrosion and tightness) the battery ground stap where it connects to the chassis, and the so called bulkhead terminals near the firewall where the power cables connect.

 

Hey there sparkenzap, thanks for the reply. I cleaned the connections in the trunk and the two at the relay/fuse boxes at the left front of the engine bay. Are there others under the hood (besides at the starter...I got that one)? If so, can you give me an approximate position? I appreciate your fast reply...all the folks here tend to jump right in with quick assistance when I need it...it's a great forum.

 

follow the wires back from the fuse block (I think you got that one) and look on the right side in the front of the ecu housing.

 

Recently, my 2000 XJR has started exhibiting a similar problem, only mine doesn't recover by just pulling out the key. I get in the car and all the courtesy lights work, etc. I turn the key to ON and all the instruments light up as usual, but when I turn it to start the car, everything goes dead - even the clock. Of course, now the trunk won't open, so I've found that if I give it a little juice at the front left fuse box terminal, whatever had shut off all the power repents and lets me (after removing the jump) start the car using its own power. This is very exasperating. The battery was new in November 2011 and the terminals look brand new. No corrosion anywhere. I suspect a relay is getting old, but I'm not sure which one could cause this much trouble. The Vehicle Care manual, page 4-22 shows relays R1-R7, but the picture shows a bunch of R1's and R7 but no R2-R6. Hard to tell which relay does what. Don't know what the + is for after Ignition+ either. Any ideas?

 

There's a ground strap under the right front area, I believe you can get to it from behind the right front wheel. I replaced this ground strap and the one in the trunk with old style ground cable. Just a thought. I was having weird no power issues sporadically and they seem to have gone away.