Is this an earthing problem?

[killerme]

To enable welding beneath the water tank, I had to take out the rock n' roll seat and the water tank unit.  When refitting I forgot about rebuilding the earth point beneath the tank unit, so when it was all back I tried to retrofit an earth onto the body of the van behind the water refill point.  Now I find I have a problem with the water tap which doesn't work.  I've checked the pump and all the connections (OK) but when I switch on the tap (not working) and then test the neg and pos connections beneath the tap with multimeter - the tap bursts into action.  Is this because I am earthing it through the multimeter?  (I'm not fantastic with electricity but I'm learning)

If this is the case can I just earth the neg cable to a nearby (green) earth connection?

[AngeloEvs]

A bit more information is needed. Is your tank under the floor with a submersible pump and when you say your are using a multimeter and using it to test the negative and positive connections under the tap are these wires going to the tap switch or where, also, which setting are you using on the multimeter (ohms, volts, etc).

Normal wiring is a 12 V feed to the tap switch and the other wire at the tap goes to the pump. The pump has two wires - one to the tap as described and the other to earth. Without a clear description of where the wires under the tap go to and from it is difficult to advise why placing the meter starts the pump, it may well be a earth connection issue but it could also be that the tap switch is faulty is you are actually measuring across wires that go to the tap.

When you made a new connection to the body work did you make sure the connection was to bare metal?



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[killerme]

Thanks for your reply AngeloEvs. I shall try to give the best response.  The tank is above the floor inside a cupboard. Yes it has a submersible pump with two wires that plug into wires that head behind the bodywork.  At the tap switch two wires going to the tap are connected to a) one wire that goes to the pump (as you suggest it should) - it has the the same colours  and b) I guess the other must be the live feed.  Using a multimeter set for 20volts, I'm putting one lead onto one of the wires going to the tap and the other lead to the other wire and it leaps into action (when already switched on).  Incidentally, I get a full 12.4 volt reading when I do this.  When I leave the van overnight, and try the tap - it does work for a few moments then stops.  I might also be only getting a 6 volt reading when I test the two pump wires though I can't be sure of this.

I tried very hard to make the connection to bare metal but it was pretty difficult because it was quite inaccessible but I did think I succeeded.  I suppose I can try attaching a wire to the point where the previous earth point attached (inside the water tank cupboard) and connecting it to a part of the engine body and see if the tap/pump works then (ie with a better earth).  

I could be completely barking up the wrong tree and its something else but I don't really know how to test the quality of the earth.

[AngeloEvs]

If it worked ok recently before you removed the tank then it does sound like the wiring may have been disturbed when you disconnected the pump. 

Essentailly, it is a case of eliminating possible causes one by one starting with pump direct to battery with new cables and then moving on to each cable individually.

To determine if its the pump that may be faulty simply disconnect the two wires that go to the pump and connect two cables to extend them so that you can attach them across the battery.

To determine that the pump switch is working just take a live feed to the cable that goes from the switch to the pump.

To determine if it's an earth, issue locate the wire from the pump that should be earthed and run a length of cable from it to the negative of the battery that supplies your pump with voltage or to good known earth point (bare metal preferably).     You can do this with the tap switched on or switch it on after you have made this temporary connection.

Also check the condition of any connections in the pump circui, particularly their connectors such as spade connectors and screw terminal blocks.   

[killerme]

right! on that first thing tomorrow. really appreciate your help.

[killerme]

Following your advice I checked pump working - OK. To test the tap switch, I disconnected the live feed into the tap and instead attached a wire going directly to the positive battery terminal.  When switched on the tap works perfectly. 
This suggests the problem lies with the live feed?  Is my earthing problem off the hook now?  But where can I go now?  I have no idea where that live feed wire goes once it heads behind the panelling.  So close and yet so far!

[AngeloEvs]

It does sound like the 12v feed is the problem. It’s a case of following the cable from the switch to the 12v source and looking for possible causes. Normally, the tap is part of the leisure electrical system which has a distribution panel such as a Zig with fuses for the various 12v electrical appliances, so also look at that if everything else appears ok.

There is a good chance the problem is something to do with the removal of the tank so look for anything that could have been disturbed. As a last resort, just run a new feed from your Distribution panel from the fused side (if you have one) or to the battery via a insertable type 10a fuse.

[killerme]

The Plot Thickens
After reading up I discovered there is a little fuse box behind the driver seat that could be that live feed.  But it doesn't look as I imagine it should. There was no input wire on the right side but there was a fuse which I removed to have a good look. There is 12.45 volts entering below left and 14.5 leaving on the left top. But there is obviously no voltage top right. Is this normal? Obviously I can now feed a wire from this fuse box into the space below the sink and power the tap but I would welcome some suggestions of what this should look like


 

[AngeloEvs]

Should have the same reading both sides of the fuse. Take that fuse out and determine which side of the fuse has a voltage as that will be the supply. If both sides of the missing fuse have a voltage then things become a bit more complicated as it may be that the fuse links both your starter and leisure battery for charging purposes but that is just a guess. If only one side of the fuse has a voltage then try and trace where the other two cables go to.

In these situations it is a case of working out where the wiring goes and trying to understand what previous owners have done. I have not seen that type of fuse box before but might be worth checking that both fuses are independent of each other and that one side does not link to the other using a common copper bus behind the terminals.

[killerme]

Spot on! That's exactly what this fuse does. The two bottom screwpoints are linked together so the power from the left also goes to the right. When I tested it first there was no power to the top right. I think the right fuse was either old or burnt but probably not working.

Things are looking much more optimistic. But I have to wait until I can get some 25 amp bullet fuses. No-one round here seems to sell them!

Thanks for giving me part of your life Angelo.