Not an MB question but still diesel. On my Fuso FG, about every tenth time I try to start it I just get a click. The starter almost always engages if I try it again. A few times it has taken 2 attempts. This began after I wired in a 12 volt connection from the battery to my truck camper, using a relay that engages when the key is turned on, to charge the truck camper battery.
It first happened after the truck had been sitting for about six weeks and I changed the batteries since I was unsure of their age. I've also since cleaned and tightened the connections at the battery and have not found any other loose connections anywhere in the starter circuit.
Does anyone know any definitive diagnostic techniques that can be applied in circumstances like this to determine if it is the starter solenoid that is at fault?
New starters for an FG are not cheap (about $450 I think) so I don't want to just replace the starter particularly since the symptoms seem identical to having a bad connection somewhere that I have not yet been able to find.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13