190E 2.6 Aux fans (electric) not engaging

[compress ignite]

1993 model
engine stumbles and shakes (loss of R.P.M.s) at idle ,in gear,with A.C.on---
after medium speed (35-50mph) runs... with no aux fans operating
Ambient temps 100 degrees "F", engine temps 80 (rising to)100 degrees[+]
"C"[nowhere near redline]
1. Where is physical location of aux fan(s) resistor?
2. Could "Heat Sink" @ idle after medium speed runs without aux fans be
affecting the engine or some of it's controls in a causitive way with
the loss of R.P.M.s and "shaking"?
'have no access to either manuals or service C.D.s for 190E 2.6
'have NOT operated vehicle,belongs to friend.

Any thoughts appreciated.