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Now it's time to assemble the unit & give it a test. The first step is to thread the cables through the cable glands.  I have cut two metre lengths of red and black 6mm automotive cable for the pump connection and the same for the battery connection.  I have also included a two metre of figure eight cable to connect to the plug pack.  Thread one length of red and black through one of the glands and the other length of red and black, along with the figure eight, through the other gland.  Pull plenty of cable through to make it easy to assemble, you can shorten this later before tightening the glands.

Now we need to connect the cables to our components.

I'll refer back to the circuit diagram for the connection details.

The cabling is quite straightforward and is done mostly with cheap automotive crimp connectors.  I wont go into the detail of fitting these, if you need a few pointers just drop me a line.  The cable connections are as follows:

• 6mm red from battery connects to the common contact on the relay
• 6mm red to the pump & the red wire to the strobe connect to the normally closed contact on the relay
• Both 6mm black cables and the black wire to the strobe are connected together in a two screw electrical connector
• The trace (with line on sheathing) side of the figure eight connects to the positive coil terminal on the relay
• The non-trace (no line on sheathing)side of the figure eight connects to the negative coil terminal on the relay

Again if you need a few pointers on making the connections just drop me a line.

Now we need to fit off the other ends of the cables. 

Battery Cable:  I simply crimped a set of battery terminal lugs to the two cables that will connect to the battery.

Plug Pack cable:  As I mentioned in part 1 the unit will be controlled by a 12v plug pack I had in the shed.  This presents us with one small consideration.  Whilst most plug packs are configured with the centre pin as positive and the outer as negative this is not always the case.  Usually the pin configuration is shown on the cover of the plug pack.  If this is not the case then a simple test with a multimeter will allow you to work out how the pins are configured.  Fortunately mine had centre positive, outer negative.  You may recall that we connected the trace side of the figure eight cable to the positive coil terminal on the relay.  In order to ensure I wire the relay coil the right way round I need to have the trace side connected to positive on my plug pack.  To acheive this I soldered the trace wire to the centre pin on the plug pack socket and the non-trace to the outer pin.  Thus we have positive inner, negative outer.  If you happen to get this wrong it should not be a disaster, you will not damage your relay it simply will not work.  If the unit fails when you test it be sure to double check the plug pack polarity.

Here you can see the completed plug pack socket next to the plug fitted on the plug pack itself.

Well I'm pleased to say that is pretty much all there is to do.  Carefully pull your cables back through the loosened glands until everything fits neatly in the enclosure.  Tighten the glands up firmly and screw the lid back on to your enclosure.  Don't forget to install the gasket before you put the lid on!

So here we have the finished product, connected to a small bilge pump for testing.

Now it's time to see it in action.  Here's a quick video of our first test!

As this unit has been designed to be pretty weatherproof I will be working on a cheaper indoor version.  I have been approached by a couple of people to build them one of these units so I will soon be posting some details on the pricing if you want to buy a completed backup unit from goanna.com.  All feedback & suggestions are welcome!