Where to start??? Been doing a lot of things to my '95 XJR6, so I only ran it to test drive. I ended up changing the battery since the old one finally wouldn't take a charge anymore. I got it to run beautifully but parked it due to gas prices and rode my bike instead, so the battery went dead again. no problem charged it and good. I kept hearing a clunking sound ( some other issue ) and after I put it up on jacks the battery was dead again. So I put it on the charger, after it was charged I got the battery light and check engine light and a no start issue and the volt meter is showing 11.5 volts. Checked the battery and it showed 12.5. I cleaned the fuse box at the battery and the bulkhead terminal. I get full voltage all the way to the alternator with or without the suppressor. So I got the bright idea of turning the key to the run position and jumping the white wire to the starter. It fires right up and runs fine. The volt meter shows 14.5 and fluctuates down to 13 depending on what I'm activating. I figured that if I used everything that maybe whatever little glitch happened would reset itself. It did not! So here I am asking for HELP!!!

 

Do not over tighten the battery positive post bolt

Never place the battery in backwards , ask me how I know

A fully charged battery is 12.75 volts at the battery post , you're at 75 % charge

Since your supercharged engine does not have a rotary switch mounted to the different GM transmission the pic below is not for your starter enable circuit but it shares the same power generation / storage circuit

Your alternator out voltage of around 13.5 is good , but not the most stable but it may be connection related and not voltage regulator related

There is a thing called parasitic drain that will drain a battery on a resting car

One quick thing you can try for that is to rotate the column switch from auto to off and fix that issue later

There are a couple of terminal post between the alternator and the battery

Editing

The battery post on the right wheel well post comes from the alternator with a tie point on the starter solenoid

This battery post on the right wheel well is on the top red line of the pic below

The next battery connection is after remove the rear bottom seat pan and there is a tie point with a terminal nut and fuse in the pic from Watto700 or b1mcp

Without your supercharger intercooler in the way someone recently got a good picture from the top looking down of his loose starter solenoid tie point nut backed off ( 13 mm )

Your alternator has to go back through these 3 terminal post to the battery before it can come back fwd to the 2 engine firewall terminal posts

But this under seat pan terminal post is work to get to so you may want to skip this point and look ElseWare on your issue

 

I put the battery on the charger again with it disconnected from the. I got 12.75 after complete charging then left it overnight to see what happened. The next morning it was at 12.54 which id in the green, but I'll keep a close eye on it. I went about pulling fuses then checking the dash to see what happens. Finally, I made to the right front fuse box in the engine compartment and after removing the #10 5 amp fuse for the alternator, ac clutch, washer pump relay the battery lamp went out. Started right up!! I pulled the relay for the washer and that did the trick for now. I'm looking for the washer reservoir and attachments before I start to mess with why the power drain at the relay. I put the the battery back on the charger to get a full charge before I try and test it and the charging system....
Thanks Parker7!! ...and now to order the parts to eliminate the rear end thunk!! Mounts and bushings an such....

 

Editing

With all the relay fuse boxes fuse # 10 . 12 . 14 , and 16 require the fuse box relay to close to be powered

The rest of the fuses bypass the relay and are wired directly to the battery positive post on the fuse box

So this cuts your problem in half , sort of

You can remove the fuses 1 - 9 on one bank or the relay in the corner of the fuse box , BUT TO RUN THE ENGINE THIS RELAY NEEDS TO STAY INSTALL3D

The engine ECU is powered by the fuse # 12 and 14 so it has to stay in place

The ECU is powered by a 2nd large relay that is controlled by the ECU and brings power back into the ECU , these 2 power sources for the ECU are needed at all times

The battery is no good if you left it disconnected overnight

The alternator fuse needs to stay in place as the alternator takes power to make power which is different than getting rid of the light

 

I failed to say that I put all the fuses back in place and left the washer relay off, seeing as there is no pump or level to control. I'm going to have the battery checked out and most likely replaced. I'm not comfortable with the constant 14.5 the volt meter is showing as its running. We,ll see later today if it starts, and again tomorrow. Thanks again!!!

 

The instrument cluster gauge is very accurate

With the engine not running or anything else electrical you are reading a static situation where you can read battery voltage

In a dynamic situation with say a cabin blower running current through the terminal posts / points you may not see the full battery voltage as a restricted point will trade voltage for current to run the blower motor

If you are concerned about the 14 . 5 alternator output the voltage regulator can be changed alone but the alternator has to come out , but you have priorities before that

Voltage regulator part # IN435 for your Denso alternator

# IN435 Voltage Regulator for Denso Alternators, 12 Volt,On: Asuna (1993-1993) , Geo (1990-1993) , Isuzu (1990-1993) , Jaguar (1993-1997) , Jaguar - Europe (1994-1997) (alternatorparts.com)

I had bad luck with E - bay vendors sending the wrong and defective part

The washer pump is under the car fwd of the right tire

 

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