12v vehicle question - identifying earths in main loom

[gazmatic]

hi all, i am trying to locate earth wires in a main vehicle loom (12v) of approx 40 wires

the car has the battery connected at the moment and there will be lives, earths, etc throughout the loom.

if i check continuity from the ground (body) to each wire itself (via a needle prick multimeter tester), to determine a link to ground, will this cause any issues with potentially having the meter on body ground at one end, and potentially then tapping into a 12v live at the other probe? would this cause a short or does the multimeter prevent any issues like this? (and the vehicle canbus / modules itself potentially being affected?)

or is there a better way to check for earths whilst the battery remains connected? disconnecting it will mean settings get lost so trying to avoid that.

cheers

 

[Geoff1946]

The car probably has a standard colour code for earth wires. Locate one of the earthing points, usually found (e.g.) near light clusters, especially in the boot, under the dashboard, near the fuse box, etc. If you can find one, and all the wires are the same colour that's the answer to your question. Alternatively, if you can locate one of the almost indecipherable wiring diagrams, from a Haynes manual or similar, that should tell you. Probing wires won't work as many load supplying wires will appear to be ground when not powered.

 

[poni]

what are you trying to fix or fit into your car?

 

[Philip01]

Predominantly if a metal car the car body is the earth, fibreglass body you’ll find Earth cables running from various accessories to a chassis point

 

[SPECIAL LOCATION]

Are there actually any regulations or guidance about any preferred colour combinations for specific functions of vehicle wiring?

Quite a few years back when I fitted the tow-bar onto our car and found some rear light cable functions not matching the designated colour in the installation instructions.....

Following a call to the tech help phoneline, I was told that historically it was not uncommon for different colour wires to be used, because they had run out of the "recommended" colour during building/installing the loom!! providing it is the correct gauge of wire for its load, the colour was very much an afterthought!!!

Plus.. As has been mentioned if the vehicle is "Negative earth" then all you need to look for are any cables that connect to the chassis!

 

[Geoff1946]

https://www.autoelectricsupplies.co.uk/resources/commonly-used-british-vehicle-wiring-colours

 

[Andy™]

Are there actually any regulations or guidance about any preferred colour combinations for specific functions of vehicle wiring?

not that i know of. pretty much every manufacturer uses different colours / combinations. some even use all the same colour with a small number prined on the cable

 

[michael8554]

How are you going to determine where each wire needs to go to without a wiring diagram ?
Some may be obvious, perhaps the longest ones go to the rear lights and petrol tank ?
You can measure the volts on the end of each wire to an earth point.
That may be 12V, or voltage from Canbus data.
That wire may require earthing to the body, or to a component which has it's own ground, how to tell which ?

 

[Bruspark]

hi all, i am trying to locate earth wires in a main vehicle loom (12v) of approx 40 wires

the car has the battery connected at the moment and there will be lives, earths, etc throughout the loom.

if i check continuity from the ground (body) to each wire itself (via a needle prick multimeter tester), to determine a link to ground, will this cause any issues with potentially having the meter on body ground at one end, and potentially then tapping into a 12v live at the other probe? would this cause a short or does the multimeter prevent any issues like this? (and the vehicle canbus / modules itself potentially being affected?)

or is there a better way to check for earths whilst the battery remains connected? disconnecting it will mean settings get lost so trying to avoid that.

cheers

Some multi-meters will blow a blow (at least a fuse) if you apply voltage to a resistance test. At 12V most good ones will just bleep angrily at you.

Check around Light clusters, Cigar lighter sockets etc for few candidate colours. What exactly are you trying to do ?