Motorhome with Sofim 8140.47 engine 2.5 TD

Hi I am getting a voltage drop in the van electrics ( not habitation ) when I turn headlights or any other item on such as brake lights / demisting fan etc.

The alternator appears to be working correctly as never had a battery starting problem or charging light never displays.

I have checked n cleaned the various earth points I can see or I am aware of to chassis points as my first thought was poor earth somewhere?

Could a faulty ignition switch cause a problem on the positive side as I cannot see in the wiring diagram that this van has a general power relay and I assume positive supply to the van electrics is done purely through the ignition switch?

Any help / suggestions appreciated.

Most Fiats seem to have a junction box near the battery, my 1994 Punto mk1 and my 1993 Ducato 10 both have, and all power for other places, both vehicle cab and caravan body, comes from this box.

As your problem is almost certainly a bad or loose earth cable you need to check all chassis earths one by one, by removing the bolt or screw concerned, cleaning up the earthing point and cable tag, and reassemble with some grease or copaslip. There will be a large earth on the starter motor body and one on the chassis nearby, but expect others elsewhere. Check also the condition of the cable where it is soldered or crimped to the tag, and of the joint itself.

I doubt the ignition switch is the main source for power. My Ducato has a switch panel for lights to the left of the steering wheel on the dashboard, [LHD] and these lights can be put on with the key in my pocket.

Thank you for your reply.

I have since posting this played with a meter and run separate positive and negative wires direct to the battery.

The problem appears to be a POOR NEGATIVE or earth as you say, so I will now have to continue trying to trace where this poor earth is to the van loom.

Any other input appreciated

i would check fuse box and fuse holders since the problem is with different electrical components you have mentioned and they have different earthing points so fuse holders may be getting weak due to age 21 years anyway always worth a shot

Hi

I believe I may have found my poor earth, the poor earth / ground is in one of the near side chassis earth points. Despite cleaning this up previously ( which made no difference ).

Today I ran a separate heavy duty battery cable direct from the negative battery terminal to the negative ground point on the near side chassis rail, so far I have not managed to get my usual voltage drop with headlights on etc.

Fingers crossed I have found the problem