Jetta MK2 Gas and Temp Gauge Problems

I have a Jetta 86 1.8L 8v CIS-E 5 speed. I have problems with the Gas Gauge, Temp Gauge and Tachometer, all of them are dead, I replaced the Instrument Cluster (3 times) in a shop and didnt do anything so my conclusion is that isnt the Instrument Cluster the problem.

I have 2 manuals, the Chilton and Haynes, I read searching the manuals that I needed to see the Bentley manual, I think that would be the fix but I live in Guatemala, Central America, so I dont have access here to buy one, the only way is buying one in USA using a freightforwarder.

Maybe someone could point me to some pictures, a site or something, I read that it is a resistor thats burn but I dont know where it is. I have some knowledge about electronis and basic mechanichs.

Any help would be greatly appreciated :banghead:

Thanks