Hi folks,

I found an issue with my Jag today, and it relates directly to the common problems found on the 308. My headlights dim when the cooling fans kick in.

What I found was, the cable between the battery and the High Power Module was bad.

With the key on, and engine not running, there was a 0.7 volt loss between the positive battery post and the big fuses.

Closer investigation using a volt meter proved the loss was in the crimp where the cable was joined to the battery post clamp. Flexing the cable made the loss change.

Another clue was that the cable was hot to the touch, something that shouldn't happen.

The cable looked brand new, but appearances don't prove anything.
I removed the cable and soldered both ends on. The loss is now 0.01 volts. I went through all the cables, measuring for voltage loss, and feeling for heat.

No other issues were found, and now the dimming is gone, and I have 14.0 volts at the engine bay fuse box.

Hopefully this helps someone. I may update my electrical troubleshooting piece, but careful measuring as per the instructions should catch this issue.

Moral of the story: you can't tell anything by saying "the cables are tight, and look good." Mine looked fresh from the factory.

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That's an odd one, how hot was it getting? I hope this isn't a common thing as it lies right under the gas tank. I've a soldering job on shortly

 

With just the key on, it was warm. Engine running, it was kind of hot to the touch. No discolouration of the insulation or anything, and you can see how clean it was. I had noticed it would crank just a bit slower on occasion, but it's nice and quick now.

 

Was that the original cable Rob?
It's certainly not a common problem in my experience.

 

The original cable looks like the same braided one that mine had. Does yours say "Made in New Zealand" too?

I've had mine replaced because of the audio gear I'm running, so haven't had this issue, but I do know how important it is to have good power (and Earth!) cables.

If you're thinking about getting them replaced, you can go one better than soldering them and go talk to your local audio shop, they should be able to use high quality cable and proper hydro-crimped lugs for a surprisingly small amount of money

 

Looks original to me.

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These things are just mass produced and if it has suffered any stress, rough handling and may I say, the effects of open celled batteries in boots/trunks.

Get rid of that Bosch battery and buy a proper closed cell AGM Calcium Varta....the only type of battery to go into the boot of a Jaguar! ;o]
By the looks of that power distribution box....somebody has been stuffing around....and it's mounted upside down.
Replace that 175 amp bus fuse with a proper 250 amp jobby as well.

Have checked/cleaned/replaced the braided earth return under the front chassis which connects engine to chassis?
This is one of the main causes of bad earth returns.

Considering the tortiously long power path on Jaguar, there are too many points that will give trouble.
Don't just look at a connection, physically disassemble it, clean it with fine emery paper, flush cl;ean with electronic cleaner spray, re-assemble and lightly coat the most exposed connectors with di-electric grease and you have no problems.

Some may think I get a bit **** about power connections but on these cars and others like them, IT IS VITAL that they are scrupulously clean to prevent power drops.
As these systems are so finicky about power levels.

Look at the length of the power path to the largest consumer, the starter motor....if everything is not spot on, you can have a power drop of 2 volts or more and the ECM is sophisticated enough to detect this leading to other issues.

 

XJay, I think you replied to the wrong thread. These comments refer to the
"Electrical Weirdness" thread.