otter switch earthing out ?

[Grant]

Hello Everyone,

Ive got a problem that keeps blowing fuse 6 and it normally happens after she has been running a while: ie hot so I suspected the fans or at least that side of things.
On investigation I found that on the otter switch there are 2 spade clips with a red and black wire connected .
I tested the wires and yes the red is positive and black is negative .
however I noticed with the wires disconnected the one that the black wire had been connected to is earthed ie is connected to the earthing permanently.( even with the wire disconnected.)
should this be the case or should the otter switch be insulated and separate with only the wires providing positive and earthing ?
I hope this makes sense.

thank you in advance for any assistance

Grant

[Gfhug]

Hello Grant, do you have the wiring diagram to hand? There are several in the knowledge section as well as the manual. Look here just above the S3 section to find a colour diagram.

viewtopic.php?f=16&t=700

These show that the otter switch is permanently earthed on one side and the other (the positive as you call it) goes to the W1 terminal of the fan relay. That black/red wire is closed to earth when the otter switch senses the temperature and makes the relay cut in to send power to the fans.

When you say you tested the wires, did you have 12volts on the red/black? That shouldn’t be.
Perhaps you can describe your test to help people to understand what you found, please.

The relay should have a green from fuse 6 to terminal C2 and a black/green from C1 to the fans.

I hope the above will help

Geoff

Edited to add, download and print off that colour diagram and keep a copy in the car as well as in the workshop, well worth doing
And if you are getting 12v on the black/red that will explain why the fuse is blowing when the car gets hot. Taking out the windscreen wipers, washer and importantly the BRAKE lights!

[MarekH]

When you say you tested the wires, did you have 12volts on the red/black? That shouldn’t be.

Yes it should.

If the water is cold and the Otter switch is not closed, everything on the earth sided terminal of the Otter switch will be tied to the earth potential and everything on the battery 12v side of the Otter switch will be tied to the battery 12v.

When the hot water activates the Otter switch, both sides of the Otter switch are now at 0v and so is the Otter switch side of the relay winding. Everything on the other side of the relay winding will be at 12v and there is a 12v drop over the relay winding, where the work is being done.

Consider the former to no different to birds sitting on a power line. They don't get electrocuted because everything, them included, sits at HT voltage. You only get a shock when you complete a circuit and current flows. When there is no circuit, no work is done, no current flows and depending on what side of the break you are sitting at, you are either tied to and sitting at either battery negative voltage level or battery positive voltage level respectively.

kind regards
Marek

[Grant]

Hi Geoff

thank you for your reply , I have previously
downloaded a copy of a 4.2 wiring diagram ( which I have copied a piece of below) and on mine it seems to show 2 wires 1 red+, 1 black earth .when I tested the red with a multi meter to the frame yes I got 12v then I tested the black wire to earth for continuity, but I must be honest I did not test across the 2 for 12v. I will do that tomorrow , but I could not see the point in having an earth wire if one of the spade terminals is already showing continuity to earth ?
and yes you are right it does blow the no6 fuse which as you say includes the brake lights which is my main concern luckily it blows the rev counter too so at least I know when it has happened !.

[Gfhug]

Marek, ok there is a low current 12v to be able to activate the relay. I was thinking of higher power which comes out of the relay when activated. But would this suggest the relay is at fault to be taking too great a load either through the relay itself or the fans? That is then overloading the fuse?

Could the fuse be incorrect rating? Or even poor contacts at the fuse holder causing the blow?
Trying to give some reasoning to help find the fault.

Geoff

[Grant]

Hi Geoff
the fuse is definitely 35 amp which is what it says in my books ,
I will check the 12v thing tomorrow but still do not understand why one of the terminals would be earthing ?
thanks again for all your thoughts and input

Grant.

[Gfhug]

Hi Grant, sorry for my confusion about the 12v at the positive side of the otter switch. Yes there should be 12v there as Marek says to activate the coil in the relay to close the terminals so that high current 12v goes to C1 and hence the fans.
Try removing the wire to the fans then short the black/red at the otter switch to earth, just remove it from the switch and touch to earth. This should give a click at the relay as it operates to show it is working. You can also check you get 12v at relay C1.
If that is all ok I would suggest one of your fans is at fault.
You can try taking jumper leads direct from battery to individual fans, via an inline fuse, to see if they run.
Do they both rotate freely by hand?

Those are the things I would do if it were my car. Good luck

Geoff

Possible dirty contacts in the relay? Have a look here at how Chris Vine sorted out his relays
http://etype.chrisvine.com/2013/12/relays-and-switches/

[mgcjag]

Hi Grant...can you post a photo of your otter switch and its spade connectors...some have 2 connectors in the center and others have one in the center with a sepetate spade attached to one of the fixing screws.....Steve

[MarekH]

Fuses blow because something downstream of the fuse draws too much current for too long. The fuse gets hot enough and melts.

I'd make a list of everything on fuse 6 and then either give them their own individual inline fuses or I'd move a green spade over to the adjacent fuse terminal and see whether the adjacent fuse blows instead. Having identified what circuit is the high current draw, I'd then look at why that might be.

The amount of current drawn will be inversely proportional to the resistance in the circuit.

kind regards
Marek

[Grant]

Hi Geoff , Steve and Merek ,

thank you all for your replies , I did post a reply earlier but it does not seem to be here ! but the gist of it was
that I took the car out again today and it was all working fine including the fans( it blew 3 fuses in a row last time out and the last one was immediately I put it in ), it was not a long journey so although the fans were both working it did not blow the Fuse which was what I wanted, to see it I could put a meter on the otter switch again.
I just do not understand how one of the spade terminals (in the pic to follow connected to the black wire) show no resistance to earth ie it is earthed . does not blow the fuse straight away,
Merek ,I did actually buy an in line fuse holder to try this but I like your idea of moving a wire across from fuse 6 and trying them out from there.I will keep you posted.
and Steve here is the picture of the otter switch and as I say the spade connected to the black wire seems to be earthing out ?


thank you all again for all your input and time.

Grant

[mgcjag]

Hi Grant.....the black wire is connected to the otter switch body....the actual wire should provide the earth but the body isn't insulated from the radiator so even if you pull the black wire off you will probably still see an earth via the screw into the radiator...it looks like new wireing
....Steve

[Grant]

Hi Steve,

yes it is new wiring I put a new engine bay loom in a couple of years back.
So I guess if the screw is earthing to the body and the wire is just a better earth that must be ok, so will will try Marek's idea of moving a green spade across and see what that shows me.

thanks again

Grant

[MarekH]

Dear Grant,

this has nothing to do with "shorting out an Otter switch". That only controls a relay winding which can only pull 0.2amps. If you "short out the Otter switch", it'll just make the fans come on.

To blow a 35amp fuse, you have to short out (i.e. connect to the chassis) either a green wire or the green/black wire before it reaches the fans or something internally inside one or both of the fans. That might be anywhere in the harness (or in the fans) and to anything that ultimately connects to a black wire or the chassis.

kind regards
Marek

[Grant]

HI Marek,
sorry for the slow reply I've only just seen your last answer
and thank you ,
as I said Im going to take your earlier advise and swap the green feed for the relay/fans over to a different fuse, when I get the chance to sit and figure out which one it is.
But I've just taken the car for a 45 minute spin and the flaming thing is not blowing at the moment so I will try and take it for a longer drive soon.

Thanks again

Grant