Swift Motorhome wiring fault

[Popty]

Hi all, I have a 2005 Swift Sundance 590RS motorhome on a Fiat Ducato chassis, it has now developed a rear lights problem, as it will be due its MOT soon I decided to check out all the exterior lights, if I switch on all lights, side/tail, rear fog, hazards, brake lights & reversing lights the fault occurs. All the rear lights alternate between dim& bright in turn with the hazard lights (hazard lights on, rear fog dim, hazards off, rear fog bright etc), so I thought its a bad earth, traced the wiring loom, from the rear lights and it enters the chassis box section just in front of the rear lights, the loom then exits the chassis rail under the plastic step pods on drivers side & passengers side foot wells, it then disappears under the rubber cab mat & up under the dash, any member got any idea where the loom is so I can check the earth wire, any help much appreciated

[Alanb]

I am not familiar with Swift wiring, but I would have expected the earth (chassis) connection to be in area of the lamp cluster, possibly via a mounting bolt. Are you tracing the common negatives into the cable forms?

 

Alan

[Brian Kirby]

Not familiar with the Make/model year, but it is fairly normal for the chassis to be used as a common earth path.

 

I'd be a bit inclined to remove both rear lights in succession and look for a black wire from one or other (or both) that is outside the main loom and goes direct to a connection on the nearest bit of the metal chassis. It may have dropped off or, after 15 years, just be making a bad connection due to corrosion.

 

What you describe suggests that there is an earth connection, but with too high a resistance. That may be because only one light is earthed and its earth connection is the culprit, or that each rear light has its own earth but one is missing/non functional.

 

If only one light is earthed, try replacing the wire with one of heavier grade cable, and see if that fixes the problem.

 

Doing as you did will put quite a high current through whatever existing earth cable is there.

 

You may also want to check the black starter battery to earth connection, which is the final return path for the circuit, as corrosion there is another possibility.

[buddy]

If you cannot find the earth connection would it be possible to run your own earths from the light clusters to the chassis ?

[Keithl]

Popty,

 

You can download a copy of the Sargent Electrical wiring schematic from here...

 

https://sargentltd.co.uk/tech-support/article/25/download/255

 

and from that hopefully trace the location of the failed earth connection.

 

Keith.

[BruceM]

Although it smacks of a faulty earth, a few questions.

 

I assume that the front lights don’t also dim in synchrony?

 

What happens if instead of putting on your hazard lights you use your indicators (left than right or vice versa)?

 

Finally, do you get the same result if you’re running your engine whilst the test is taking place?