Repeating and building on what ah-kay said, the glow relay temp switch is usually on the side of the head by the IP. The bigger device on the side of the head is the gauge sender. The 3-prong temp switch is for the fans at high speed (lower temp trip) and AC compressor cutoff (higher temp trip). The temp sensor beside the 3-prong’er is for EDS.

The fans won’t trigger by disconnecting the 3-prong switch. 2 posts have to be bridged. I don’t remember which ones.

There’s a refrigerant pressure switch (no pigtails) that interrupts the signal to compressor clutch if system pressure is insufficient. There’s a refrigerant temp switch (with pigtails) that triggers the fans (mentioned above). Separate circuits makes Diesel300’s point that engaging the compressor doesn’t automatically trigger the fans. Conversely, it’s been reported that in really hot conditions, the fans come on at low speed even with the compressor off.

From your comment that the glow relay isn’t working as expected and that it’s wired to the 3-prong switch, I suspect the harness doesn’t properly connect engine and body. When restarting a hot engine with afterglow, the glow light will flash for less than a second, even if it might keep the glow plugs energized longer. Was it doing this with the 602?

Sixto
98 E320s sedan and wagon
02 C320 wagon