What is this? Its on a W124 below ABS
 

Check out pic. It's this white thing bolted to area under the ABS unit with a couple of wires going to it. It's missing on one of my cars.

Thanks

I believe that it is a ceramic fuse related to a/c and the fan. I had my indy switch out my compressor last year and converted to R134 (I know, I know...) and in the process he removed that fuse completely as part of a different switch set up he put in to accommodate the conversion.

Axillary Fan Resistor - It controls the multi speed functions of the Electric fan in front of radiator. I believe it is 3 speed. Low whenever A/C is engaged, Medium when temps reach a certain temperature, and then High whenever it gets really warm. It has been a while but mine was cracked on the 300TDT when I got it so in making sure my coolant system was intact, I replaced it.

It is the fan resistor. Drops voltage to the electric cooling fan(s) for low speed operation.

The fans are two speeds on the 124. There are two relays in the fusebox/relay box. One sends power to the fan resistor to activate low speed. This is triggered by the a/c high-side pressure (red, possibly green) switch on the a/c dryer.

High speed sends full battery voltage directly to the electric fans, bypassing the resistor entirely. High speed is actuated by the second relay in the fusebox. High speed operation is triggered by engine coolant temperature reaching 105C.

So long as the wires are connected together, there is no harm in a missing fan resistor. You will get high speed fan operation when only low speed is required, but there is no real harm in that. Bit more noise is about it.

Can you hear the fan kicks on when it gets like 100? What temps does the fan kick on in a W124? I normally run at 80C but when i do sit idle the temps rise pretty fast, ive never sat long enough to see if they come on at 120 degrees cause im scared ill mess up something.

I've never actually seen the fan come on on the car that does not have this. Should it even though it does'nt have this part? I'll get one. The car i took the pic of with it it does come on. Thanks yall. I'll get one.

The car without runs about 85 to 95 regularly depending on load. Never gotten above 100 and doesn't heat up sitting at idle.