OK, looking for some straws to grasp onto.

I have been having electrical problems with my 1999 XK8 (that might have been a redundant statement).

I recently replaced the alternator and battery. Prior to that, I was not getting the red warning light on the dash, but it I was getting a bunch of random warning lights (transmission, traction control, etc) that I suspected were actually being cause by low voltage. Prior to changing the battery, it also seemed like the batter would die if I let the car sit for a day or two, so I suspected

The current symptoms are as follows. With the battery fully charged, it shows 12.6ish volts if I take a multimeter to the terminals. When I connect the battery, the voltmeter inside the car reads 9-10V. If I try to start the car, it will not crank. No click, nothing. Sometimes with the key off, I still get a 9V reading on the car's volt gauge.

The windows roll up and down in a slightly lethargic way, and the lights work, but seem dim.

If I disconnect the ground, and put a multimeter in between the terminal and ground cable, I see 12V. Measuring the amps being pulled though, I get pretty close to nothing. Opening the doors and doing the fuse-pulling thing, most of that seems to be on circuits that I'd expect to be drawing current with to doors open (which is necessary to access most of the fuses!). The exception is the instrument panel circuit, though maybe that's the clock.

Fuse #2 in the engine compartment is OK. I tried touching the + and - battery cables together, with no effect. I tried dropping the car into neutral before starting, but nothing.

Any thoughts? Please assume, despite having tried a bunch of things, that I am very stupid and completely clueless about this car's electrical system.

 

By the way, I love this car/I hate this car. I am at the point that I just want it to run well enough that I can sell it. But if I get it running that well, I will love driving it so much that I couldn't possibly part with it!

 

How are you measuring amps?

 

Check the integrity of the leads and tightness of the connections in the High Power Protection Module (see item 5):



Issues here can cause the symptoms you describe.

Graham

 

"How are you measuring amps?"

Probably somewhat not right. I plug the red lead into the Amp port on the multimeter, and set the range to 10A. I then pulled one of the cables off the battery, and touched one lead from the multimeter to the battery terminal and the other to the cable. No reading. I then decreased the range on the multimeter until I was reading milliamps, but still just noise.

Now, the trunk was open and the trunk lights did not light when I was doing this, so, why wouldn't read zero amps after all? So, I think I forgot how to do this right.

 

Here is a little more info. Today I checked the voltage at each of the connectors in the high power module. Everything read at battery voltage. I did not try to peel back the insulation to get at the wires themselves, but I did check voltage at all the fuse boxes, and they were ok. I wanted to check power at the "false bulkhead connector," which seems to be on the circuit I'm most interested in, but could not find said connector.

I also wiggle/jostled/pulled the wires at the high power module, but no change.

Other new observations of note... When I put the key into to the "start" position, a low pitched whirring starts ... sounds like it is coming from the engine compartment, but my arms are ten feet too short and lacking at least three joint for me to be able to localize it beyond that.

Also, when I try to start the car, the voltmeter on the IP reads 10V. When I switch the key off (and remove it), the voltmeter continues to read 10V (and the temperature gauge also reads whatever it was reading. If I put the key to acc, then the voltmeter goes back to zero and remains there when I remove the key. I have not paid attention before, so am not sure if this is expected behavior, or another symptom.

 

Jon. Did you change alternator yourself? I wonder if a bad connection exists at the alternator (the small wires, not the big battery cable).

It's been a while since I looked at the wire diagram for the alternator maybe someone could remind us what those wires go to (gauge on dash?).

Let's brake down the issues:
1) 10 volt shown at idiot gauge.
Take a volt reading elsewhere up around dash (fuse boxes, cigar lighter I don't trust the idiot guage)

2) reduced current. 12volts doesn't have much force. We've seen nearly invisible corrosion cause issues with current. Did you brush battery terminals and connectors shiny?

Do you get same volt reading (a) battery + to battery-; (b) battery + to chassis? [Analysing ground connection from battery to chassis.]

John

 

Let's back up and reassess.

Testing voltage at a cable is not the same as verifying it's current carrying capacity. Under load, a corroded connection heats up and dramatically​ increases in resistance to the point that the needed current can not flow to the load. The earlier suggestion to remove/inspect/clean was spot on. Do the battery cables, grounds, junction box.

The voltmeter reading is probably inaccurate. Check voltage at some other junction in the cabin, or better still, check it at the gauge. I wouldn't exactly call the factory installed voltmeter a precision instrument.