What’s the worst that can happen? Earth cable / negative cable

[Cush]

So …
Had a new starter battery professionally fitted a couple of years ago at the same as solar and new LA leisure’s.

Today when putting the victron ip charger on the starter battery I noticed an un attached black cable that is the perfect length and curve to fit on an original threaded stud on the -ve terminal bus bar.

An explanation could be that the nut came off or wasn’t replaced.

In hindsight, the only thing I’ve felt was an unconfirmed suspicion that the fridge didn’t cool properly on 12v when driving but it wasn’t a big enough a concern to investigate further as I didn’t really expect much.

Any way to check with a multimeter if it is the fridge?

If it’s not, what possible harm could connecting an unknown -ve / earth do?

TIA. Cush

 

[oldiesontour]

If you don't have measuring equipment you could connect to - via a fuse (so long as it isn't very thin wire 10amp) will run fridge and blow before wire is damaged)

 

[Phill D]

its a bit hit and miss just to connect it if you dont have a meter to check or track the wire!

 

[JustifiedAncient]

If you have a decent multimeter to hand, I would start by seeing if there is any voltage between the vehicle chassis and the mystery black cable. If there is none, then next check the resistance between chassis and the cable. I suspect that there is be very little as there will be other return paths to the battery. If so, then connecting it to the -ve terminal should be safe and will help to reduce voltage drop with higher current loads (such as your fridge on 12v).

 

[DBK]

Does the terminal look as if it has ever been used? Looms often have wire which may not be used in your specific vehicle. See if the terminal looks crushed in places.

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[GeoffnDee]

If your Motorhome has a EM40 fuse module fitted (often behind the drivers seat) , this controls the 12v power supply to the fridge heater element and there should be a connection from the negative (and positive) starter battery terminal going to it . Perhaps this is/was the purpose of your spare black cable .

 

[Gromett]

Personally. I would want to know what was at the other end before connecting.

 

[Burgo]

Not every manufacturer / fitter abides by a common standard for colour codes on wires - just because it's black doesn't necessarily mean its a - ve. Could just as easily be switched live..

 

[Cush]

its a bit hit and miss just to connect it if you dont have a meter to check or track the wire!

I guess that’s what I’m asking. How do I work out which item it is for? Or illuminate it being the fridge?

Does the terminal look as if it has ever been used? Looms often have wire which may not be used in your specific vehicle. See if the terminal looks crushed in places.

It couldn’t be a more bespoke cable to fit on that free stud which appears to have had a nut on it. The ring fitting that is crimped on also has signs of being bolted down.

If your Motorhome has a EM40 fuse module fitted (often behind the drivers seat) , this controls the 12v power supply to the fridge heater element and there should be a connection from the negative (and positive) starter battery terminal going to it . Perhaps this is/was the purpose of your spare black cable .

My van doesn’t have that sort of set up. Sargent system in this one.

Personally. I would want to know what was at the other end before connecting.

Very much so. Any suggestions how I go about that?

Not every manufacturer / fitter abides by a common standard for colour codes on wires - just because it's black doesn't necessarily mean it’s a - ve. Could just as easily be switched live..

Im pretty sure this was part of autotrails original loom. I will have a read about those switched lives. This cable definitely went to that threaded stud. Just not sure if it should anymore an£ what it was for.

Thanks everyone for your replies.

Key thing to move forwards is to eliminate it from being the fridge. How do I check this or the cable’s continuity to the fridge over a 5m distance?

Edit - just remembered I have a large coil of wire. Going to try and make an extension to the wire in question and do a continuity check. Will let you know how I get on.

 

[Gromett]

Very much so. Any suggestions how I go about that?

Edit - just remembered I have a large coil of wire. Going to try and make an extension to the wire in question and do a continuity check. Will let you know how I get on.

That is probably the quickest way to do it. If not then a wire tracer could be used. I am NOT recommending this one specifically as I have not used this one.
But you can get tools like this where you can track the wire back and locate it exactly.

https://www.amazon.co.uk/dp/B0811P7SCT/?tag=mhf04-21

I would check continuity between the chassis and this cable 1st though.

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[GeoffnDee]

The EM40 is a Sargent item used for fridge 12v operation from about 2007 onwards but if your Autotrail has an earlier Sargent PSU2007 and a fridge /freezer fitted there should be a direct negative battery terminal (black cable) connection between the starter battery and the fridge/freeze .

 

[TheBig1]

if it's an autotrail, the fridge power comes via the sargant unit. If you don't have 12v and earth to the element, the fridge will switch to gas. The extra wires I have seen in battery compartments are generally just extra unused parts of the standard loom. Normally nothing to worry about unless something isn't working. Never be tempted to connect a wire that never was before. If it is dull and slightly tarnished and not been compressed onto a lug at some stage it can likely be ignored

 

[Cush]

That is probably the quickest way to do it. If not then a wire tracer could be used. I am NOT recommending this one specifically as I have not used this one.
But you can get tools like this where you can track the wire back and locate it exactly.

https://www.amazon.co.uk/dp/B0811P7SCT/?tag=mhf04-21

I would check continuity between the chassis and this cable 1st though.

Thank you. Will do that today when I go to storage. Will also look for any voltage as suggested by JustifiedAncient

The EM40 is a Sargent item used for fridge 12v operation from about 2007 onwards but if your Autotrail has an earlier Sargent PSU2007 and a fridge /freezer fitted there should be a direct negative battery terminal (black cable) connection between the starter battery and the fridge/freeze .

Thanks GeoffnDee. It is indeed a PSU2007. I will try to rig up a continuity check between one end and the same looking cable at the back of the fridge.

if it's an autotrail, the fridge power comes via the sargant unit. If you don't have 12v and earth to the element, the fridge will switch to gas. The extra wires I have seen in battery compartments are generally just extra unused parts of the standard loom. Normally nothing to worry about unless something isn't working. Never be tempted to connect a wire that never was before. If it is dull and slightly tarnished and not been compressed onto a lug at some stage it can likely be ignored

Thanks TheBig1. My old fridge doesn’t have an automatic change over. Appreciate the opinion on the loom.

 

[eddie]

If it’s a Fiat, it’s probably for an option your van doesn’t have

Seen it many times

 

[GeoffnDee]

Cush If you do not have them already , there are Sargent wiring diagrams for the (Fiat X244 ? ) Autotrail electrical system , using a PSU2007 , on page 4 of Motorhome Technical Articles section of Resources (bottom of this page) which could be useful to you in checking things out.

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[Cush]

Cush If you do not have them already , there are Sargent wiring diagrams for the (Fiat X244 ? ) Autotrail electrical system , using a PSU2007 , on page 4 of Motorhome Technical Articles section of Resources (bottom of this page) which could be useful to you in checking things out.

Thanks. GeoffnDee I have those. Unfortunately black wire only shown at -venfor a short distance before turning in to the white/orange.

Edit- didn’t. Actually have the wiring harness diagrams. Thanks so much for the pointer

 

[Cush]

Took some photos and meter readings earlier…

No voltage between the end of the cable and chassis.
Same voltage between end of cable and +ve terminal as across the battery.

Think

these pics below show it was once connected. It’s purpose, I know not.

 

[sonny]

It looks like it’s been loose for a while

 

[eddie]

Took some photos and meter readings earlier…

No voltage between the end of the cable and chassis.
Same voltage between end of cable and +ve terminal as across the battery.

ThinkView attachment 873624 these pics below show it was once connected. It’s purpose, I know not.View attachment 873625

That isn't a Fiat connection

 

[Boldly]

Is your van quite old? All the -ve cables look less than perfect.

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[Cush]

Is your van quite old? All the -ve cables look less than perfect.

2003

 

[Cush]

That isn't a Fiat connection

Autotrail

 

[Cush]

It looks like it’s been loose for a while

Possibly 2 years

 

[GeoffnDee]

Do you have a fridge or a larger fridge/freezer in the Motorhome

 

[Cush]

Do you have a fridge or a larger fridge/freezer in the Motorhome

A Dometic / Electrolux 3 way. Too old for auto changeover RM 6400

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[GeoffnDee]

As you are getting a voltage reading between the black cable and the starter battery positive terminal the black cable must be linked to the starter battery negative terminal through the white/orange habitation negative wiring and/or through the negative van body connections of the batteries . As both starter and leisure batteries are linked to the white/orange cable and the van body for negative battery circuits I think that if you can trace the black cable back and you find that it joins the white/orange cable this would allow it to be connected to the starter battery negative terminal to allow a more direct circuit for the negative side. (which may have been its purpose)

 

[Cush]

GeoffnDee, great explanation that makes perfect sense. Thank you so much.

Cush