electrical ground issue

About two weeks ago, I drove about ten miles to a Jag dealer to look at i-pace. After test drive, I went to start the 575 and no go with F1 tranny icon on.
Sent it off to the mechanic who had just replaced my F1 clutch sensor. It was a dead battery. Battery would accept a charge but then go dead, and it was 3 years old and has been on a maintainer when not in use, usually with battery ground switch in off position so that battery negative terminal was not connected to car. Bought a new battery and everything was fine.

Today, I was adding a new electrical item to my car which needed to be grounded. I turned on battery switch to connect battery negative terminal to car structure and I found 24 ohms everywhere I measured grounds. I disconnected positive terminal and get 0.4 ohms.
Turn battery ground switch to disconnect battery ground from car and get 108 K ohms.

Any ideas why this happens?

 

A learned guess from a friend suggests a voltage leak/short in a relay or ecu. Will try to isolate cause.

 

Going through all relays and ECU and connectors unitl I find cause. It sure would be nice if there was a real wiring diagram to go by. I am used to having complete diagrams even down to pin-outs on connectors.

 

I have two, ABS circuit and secondary air pump circuit. I will raise front end on ramps to check out the two items tomorrow.
Meanwhile I need to have someone look at their fuse boxes over by battery and tell me if I have the correct arrangement on mine.
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How would either of those methods isolate the module or connector at fault?

 

Bill
That alignment looks like pic in WSM except that boxes L and M have swapped positions.
You can check by pulling relay for secondary air pump in the fuse/relay box on driver side and check voltage to pin 7 with the FP 4 fuse in and out, 12 v with fuse in , 0 v with fuse out.

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here are schematics for box L and M, with approx wire gage and colors
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these are based upon what I saw after removing lower covers
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I wonder why Ferrari put 80 A fuses on smaller gage wire than the 60A fuses

 

Most wires from boxes L and M go down the side passenger panel, turn inward behind inner fender panel and pass through firewall to main electrical panel in passenger footwell.
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just like schematic from WSM

I will now try to track them down.

 

I think you can leave them alone as long as you label them correctly. It tis easy to reverse poison by using a small screwdriver on two tabs between the two holders and pull up. Then remove screw holding plate to wall and remove other other holder from plate and then reinstall in reverse order. I suspect if you look closely behind the holders you will see that cables are crossed.

 

Bill
Your arrangement is correct. The pic in the WSM is backwards. L is M, and M is L. After I traced 6 of the wires my setup now looks like yours. Only the two master wires and the F 1 wire come into passenger footwell area. The 2 fan and air pump wires go over to the relay box on driver side of engine bay. I am still trying to trace the ABS and AC lines. I will post new diagrams when I finish.

So my voltage leak is from the two master circuit wires!

 

Past fuses from battery. I will start pulling fuses inside car.

 

ignore post 11

 

Well, after pulling and reinserting all fuses and relays, the problem is gone. In process it was fuse 30 for door lights which indicated something. When I went to pull connector at door jamb I noticed that the locking mechanism was not fully down on the connector. Removed and reinserted completely and locked down and now no issue. Go figure.

The door had been taken apart during one of the PO time, and I had to fix the pull as it was not aligned when I bought it. Maybe they had pulled the jamb connector for some reason?

Now I can get back to driving it.