Still struggling with failed roof ligting

[wotme]

I'm getting juice through the little rocker switch to the 4 lamps but am stumped how to check the earth. I've removed one of the lamp holders but all that shows is cables disappearing into the plastic moulding. I've been told the earth must follow through a trunking back to the battery but that's really not much help. I was hoping there might be an accessible earth connection somewhere close to the light cluster. I know the chances of someone working on a similar unit is very slim but I really don't fancy paying mega bucks unless I have to

 

[Diabalo]

The 4 lamps will have a common return, get one out and test it then trace it back to source.

 

[mitzimad]

test for 12v to a known earth then work down the line probably find the other end of the feed wire is in one of the lockers where it joins with the lights under them

 

[Sandancers]

Can you get one of the earth (neg) wires disconnected and take it via an additional wire back to a known good earth, maybe battery neg ? Then if the light comes on you have confirmed bad earth before you go any further.

 

[wotme]

Thanks for all your replies. Okay it looks like the 4 lamp cluster will need to be taken down Hmmm! Easier said than done, assuming there's enough cable to leave a gap to work in. I'm guessing it will need supporting in some way. In addition to the 4 lamps that are not working there are 8 others mounted in the ceiling / roof space that are working fine so does that indicate the problem is close to the cluster possible where the 4 lamps have a dodgy common earth connection?

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[andy63]

I know these things can look a bit complex with a load of wires linking the 4 lights but there can only be the live and negative wires running in to the fitting..
Its unlikely there will be a nearby chassis return point given mh construction materials

I've removed one of the lamp holders but all that shows is cables disappearing into the plastic moulding.

One side of the fitting will be the supply...the other side the return wire ..if you suspect a problem with the negative side a very basic test would be to check it's resistance to s known good negative.. The resistance should be in point 1or 2 of an ohm if you can measure it..
Better tested under load mind with a voltage applied and a test lamp.. If the test lamp is dull you have a high resistance in the circuit..
A very useful tool for quickly checking circuits for supply and negative is a power probe.. But its not a cheap tool..
Andy