l wanna know how to run a toggle switch to my auxillary fan, because the relay fuse slot for the fan does not have any current running to it so there is no way to know if the relay is bad, there is no current running to it.

Its for AC and defrost.Your Fan on water pump should handle cooling,unless the clutch is not working,its a replaceable item.First insure its working,and the block is clean,and rad.Not uncommon to replace with new rad. that is not clogged up.Use MB antifreeze only.You can modify thermostat,till you get money,by drilling holes in it.dieselgiant, has tips.

There is a fair chance that a ballast resistor was used in an '86 300E aux. fan circuit if an '83 S-class is any guide. These burn out & the aux fan stops. They r a coil of silvery wire wrapped around a white form which is probably porcelain. They may be in a metal box which has holes drilled in it.

They cost about Australian $80 to buy but r easy to install. That would be around US $70, maybe less depending on tax regimes. Mine burned out the January before last so l know.

Owned an '83 W126 coupe 8 years & l think l have answered this question before.

Otherwise, pull the relay, remove the metal cover & see where the connection to the primary coil is. Or check with a multimeter. If the relay clicks when supplied with 19 - 12 volts it is probably good.

I'd go for the ballast resistor first though.

It would make more sense to get it fixed properly,,,,,take it to the dealer and bite the bullet.

Why would you run a separate switch? There is a possibility that you will one day forget to turn it on and possibly overheat the engine or you may forget to turn it off and drain the battery in the process. Just fix it properly and be done with it.