I've got a 1999 Fiat 2.8 TD based Autotrail Mohican.
I had all sorts of silly little electrical problems like dull headlights, rear-view camera shutting down when I operated the electric windows, culminating in the alarm system working when it felt like it would.
I got on to Cobra alarms and got a lot of help in tracing the Alarm fault, Mr Brown from Cobra intended to get me to reset my alarm over the phone under his instructions. Before he could do that he told me to check that I had good Earths at certain points.
I took my multi-meter, connected the black to the battery negative and with the meter set to the resistance range, checked the various Earth resistances back to the battery. I was expecting in the region of 0.2Ω to 0.5 Ω, but what I got was about 16Ω, so this raised my suspicions right away. I rigged a temporary Earth with a length of cable and a couple of crock clips and suddenly all my alarm faults were gone.
Since then I have checked all the Earths throughout, both on the vehicle side and the caravan side. I found them all to be rusty, dry and high resistance.
I cleaned them all up, re-terminated where necessary, covered both surfaces with a good water proof grease (I used Vaseline), I put shake-proof washers between mating faces, so they would bite into each other and make good electrical contact. I also put a good stout cable from one of the vehicle Earth points to one of the main caravan Earth points. Now when I do resistance checks between any Earth points on any part of the whole motor home, they are all less than 1Ω.
That’s what I did, but the results on the motorhome are; no alarm problems, my headlights are pure bright blue/white, electric windows are much quicker, rear-view camera does not die on me, starter turns faster and the electrics generally seem sharper.
My advice; if you have electrical problems you cannot sort, check both the supply lines and the Earth returns. Do this before you start buying ad replacing thing that may be serviceable. The Earth is the one that usually gets forgotten, but remember the power goes out on the positive and returns through the negative (Earth), so they are equally important.
RexH