Technical Battery to body ground connection?

[Synthman]

Hi all. Does anyone know how the battery negative is connected to to the body and the electronics? I can see the connection to the gear box which I have cleaned so I now have 0 Ohms from the battery to the engine but I cannot find the connection to the body and all of the electronics and I am getting over 1V dropped just by putting the hazards on (only 10mV drop to the engine). The rather poor Haynes online manual suggests a second connection from the engine but it is as best vague as to where that is and the workshop reference I got from ebay is incomplete for that area and has no electrical schematic as the files appear to be corrupt with just blank pages. My issue is for the MOT I had an advisory note as using the indicators makes the servos in the headlamps bounce up and down! Thanks

 

[chris3234]

Hi all. Does anyone know how the battery negative is connected to to the body and the electronics? I can see the connection to the gear box which I have cleaned so I now have 0 Ohms from the battery to the engine but I cannot find the connection to the body and all of the electronics and I am getting over 1V dropped just by putting the hazards on (only 10mV drop to the engine). The rather poor Haynes online manual suggests a second connection from the engine but it is as best vague as to where that is and the workshop reference I got from ebay is incomplete for that area and has no electrical schematic as the files appear to be corrupt with just blank pages. My issue is for the MOT I had an advisory note as using the indicators makes the servos in the headlamps bounce up and down! Thanks

I'd have thought the body computer earth point would be somewhere around the body computer/inside fuse box most like around the footwell area

 

[varesecrazy]

Hi

On other fiat cars
Its 1 long cable with a tag half way down it attatched to the body

It may be hidden from view..under the battery tray ...

Do let us know what you find !

 

[Synthman]

Hi

On other fiat cars
Its 1 long cable with a tag half way down it attatched to the body

It may be hidden from view..under the battery tray ...

Do let us know what you find !

Oh no! I can see that but cannot see how it is attached to the car as I cannot get behind it! That is where the problem is as I get 0 Ohms to the metal that is sticking out but there is a resistance to the metal it is attached to. Not sure if I have to take the bumper or the wing off to get to it. Thanks

 

[Synthman]

I'd have thought the body computer earth point would be somewhere around the body computer/inside fuse box most like around the footwell area

Ok thanks, yes the ECU, etc have nice big studs and nuts attaching them too the body, I get zero Ohms throughout the body and to the individual boxes, it's the battery and engine where I am seeing a large volt drop although thinking about it the lights and associated electronics share the same ground so they should all be at the same potential. It's tricky to trace without a schematic. Thanks

 

[Synthman]

Thanks for the tips, electrical gremlins have gone! Turns out the bit I could not see in the middle of the battery negative cable had a bolt next to it under the glow plug relay behind the wires that was nicely corroded. 13mm socket and extension bar plus needed to remove battery and battery tray although it may be accessible from underneath if you don't have a sump guard. To test just turn on the ignition (no need to start the engine) and the hazard lights. Measure the voltage between the battery negative and any clean, bolt or exposed metal on the bulkhead, if you measure more than 20mV it could be the start of electrical problems, I was seeing in excess of 1V and having issues with the headlight motors moving with the hazards on, radio switching off when the electrical load changed, like winding windows up or down and other unexpected electrical issues. It's also worth checking the connection to the gear box as that it the ground for the engine. Hope that helps. BTW 2012 1.3Tdi Trekking

 

[varesecrazy]

Glad you found it ok.

If you struggled.. I would recommend this as a great starting point

The Electrical gremlin thread....... | FIAT Grande Punto

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