Multimeter Reading Negative Postive

[smitch6]

just tested my electrics on my 12v boat

it is reading -12.6v

yes i have the red on the positive and the black on earth wiring

i gather i have something shorting out somewhere?

if i swap the connectors round so black is on positive and red on earth it reads 12.6v as normal

is it a short somewhere????

[grendel]

is your battery connected the right way round? what is the voltage across the battery + and - and are you sure the wiring hasnt been crossed somewhere.

[ExUserGone]

Are the leads the right way round in the multimeter?

[MBA Marine]

Do you have a Freeman?

[smitch6]

yes the batteries are correct and yes the leads are correct on the multimeter

and no i don't have a freeman :)

it's a vanguard thunderjet, 17' with 4 stroke 15hp outboard

[grendel]

sounds like the wiring may be crossed somewhere between the battery and where you tested.

[ExUserGone]

It won't have hurt any lighting circuits on the boat and a bilge pump would probably just spin the wrong way and not pump but it will wreck the charging regulator in the outboard if you don't sort it.

[smitch6]

i only noticed it the other day after i ran the batteries flat after leaving the coolbox running all night lol

[thingamybob]

37 minutes ago, smitch6 said:

just tested my electrics on my 12v boat

it is reading -12.6v

yes i have the red on the positive and the black on earth wiring

i gather i have something shorting out somewhere?

if i swap the connectors round so black is on positive and red on earth it reads 12.6v as normal

is it a short somewhere????

If you had a short a sub fuse or the main fuse would have blown, provided you have the proper fuses in place. Otherwise, no idea. Has anybody other than you been working on your electrics?

[smitch6]

no i'm the only person that i know of lol

i did fit a cigar aux socket with 2x usb's built in but i've also done other stuff at the same time

i'll go down tomorrow and take all the fuses out and start from scratch

there isn't much there so it won't take too long hopefully

[thingamybob]

Just now, smitch6 said:

no i'm the only person that i know of lol

i did fit a cigar aux socket with 2x usb's built in but i've also done other stuff at the same time

i'll go down tomorrow and take all the fuses out and start from scratch

there isn't much there so it won't take too long hopefully

I can't see how that would change the polarity. Best of luck mate, let us al know how you get on. I take it that you tested the voltage at the battery terminals. If it is ok there then follow the wiring through. You should have a main fuse and then on to a distribution box as in house wiring. Test the input there and see what happens. Check if all outgoing circuits give the correct reading. 

[Vaughan]

Be very careful that a cigar lighter socket must be wired to correct polarity. Is this where you tested it with the multimeter?

If so do not plug anything in, such as a TV or a mobile, or you will probably wreck it.

I understand what MBA says about Freemans as some of the old old ones, like American boats, were wired positive earth.

[BrundallNavy]

Take off the battery terminals and check the battery on its own, if you still get the - reading the battery is shorting out inside.  You can always check the multi meter by putting it on your car battery to check if it's working correctly.

Doug.

[Islander]

I think the first job here is to ensure your meter is reading correctly. Try it on your car battery or even a torch battery, AA C or D cell making sure the polarity is reading correctly. If all ok, work from the battery terminals forward. 

Colin

[Viking23]

If you could show a front view of the multimeter, with it set to the switch position you used, with the leads in the used position, we can eliminate incorrect use of the meter.

Just a thought...

Richard

[tjg1677]

some very good advice given, best bit is check your meter to make sure it is set to DC and test it on a known source. If it still reads the same then meter is duff.

Systematically go through the boat starting at the battery, if the readings are reversed at the battery and the battery terminals are on the right way, then I am baffled.

if starting point reads ok, from the battery work along every circuit in turn to eliminate the crossover if there is one. A favourite is where circuits are split via terminal blocks, it is not uncommon to find wires swapped over here.

You didnt say where you took the original measurement from, that may help as if it was a 12v outlet, they are very easy to get wrong, I have done it myself by reversing the spade connectors on the back of them. 12v incandescent lighting will work on any polarity but led and flourescent lights are polarity sensitive.  Motors will run in reverse and electronic equipment will fry.

 

hth

trev

[Baitrunner]

I have seen multi meters with a polarity reverse switch on them. Basically swaps the neg and live over within the meter. Very confusing if you have it in the wrong position!!!

[smitch6]

okies been down the boat this morning again

it turns out the multimeter is faulty

took my other meter down with me to double check

the black is in the common (middle) port which is how my other one is also

and with my 2nd meter all reads fine

with the meter i had on the boat it still reads - so the meter must be faulty

so that'll go back and i'll get it swapped

thanks for all your help peeps