94 e320 aux cooling fan ?
 

I've had sporadic weirdness from the aux fans on this car for awhile now, and I know 94 is different than 95 or the earlier models.
So bare with me and let's start over.

Low speed, both fans, works with the AC on.

I can apply 12v+ to either side of the resistor and get low or high depending
on which side I power.

I can short the AC switch and get low speed, which stands to reason since they work with the AC.

Previously, when pulling the 2 pin plug off the temp sender on the thermostat housing, that would engage both fans on high.
Now it does not.

What I can do, is apply a ground to one side of that plug (the one that isn't already grounded), and they come on high.
At warm idle I get 750ish ohms on that sensor, it decreases as temp rises but it's quite hard to get this car to get too warm so I can't test it very well.
In fact the only time it's ever gotten hot is after hard interstate driving in 100+F weather with the AC on and then going immediately into stop and go traffic for an extended time, that was a while ago.

Fuses good, including on the relays under the cover.

Assuming the pull the plug/high fan test is valid, where do I go from there?
Of note it's no longer 90+F here, more like 55ish.
Is there some logic going on as to when the high speed should work or is it a straight analog circuit?

Have you check the high speed relay?

Sent from my XT1710-02 using Tapatalk

No, but I can apply a ground to one pin of the 2 pin plug on the temp sender on top of the t-stat housing and get high speed operation on both fans.