M880 light problems

[Milt51]

Okay, here goes... when I bought my M880 last summer I discovered that it had no lights of any kind whatsoever. I determined that there is power to the three lever switch, but nothing past there. I assumed the switch was bad. Now I have recieved my new-in-the-box three lever switch and .... you guessed it, still no lights of any kind anywhere. I have dealt with automotive wiring issues in the past, but this is a stumper. I also noticed that the small harness that connectes in the lower left corner of the firewall plug that feeds the heater motor is missing. I can't see that being a factor, but without deharnessing my parts truck, I'm not sure where to look first. Any ideas, anyone?

 

[Bob H]

Grounds

99.5% of light issues are ground related the other .5% is either the 3 lever or the relay next to the fuse block.
The 3 lever needs to be set to service druve for the factory light switch to get power.

 

[N1265]

1) Make sure the body of the truck has a good ground, on my truck there is a ground wire that goes to the neg side of the battery to the left fender.

2) When you say " nothing past there " does your horn work in service drive ?

3) If horn works in service drive, check for power at the factory head light switch coming from the 3-lever switch. it should be wire #6 ( I think )

 

[N1265]

1) Make sure the body of the truck has a good ground, on my truck there is a ground wire that goes to the neg side of the battery to the left fender.

2) When you say " nothing past there " does your horn work in service drive ?

3) If horn works in service drive, check for power at the factory head light switch coming from the 3-lever switch. it should be wire #6 ( I think )

 

[m880 unimog]

all sound advice,ground cables are the point where the circuit is most likely to fail due to corrosion caused by disimilar metals-i have a mobile 'fly lead' that has led indication of any dc voltage-you can switch it between pos and neg-it,s really handy-got in a wal mart last time i was over.enables you to test for live,and/or put a know negative [ or positive ] ground anywhere the cables will reach.