I wanted to share my experience with troubleshooting the temperature gauge in my 1985 325e. I initially focused on the C101 connector and found no continuity between the engine side (female) and chassis side (male). After cleaning the contacts with Deox-IT, I inserted some scraps of copper wire into the female side to improve the connection, which finally established continuity. However, this didn't resolve the gauge issue.
Next, I examined the motor, particularly the sensors (about 3 of them) within the thermostat housing. I realized that the gauge sensor was the one with a single blade and a brown/white wire. Contrary to online suggestions pointing to other sensors, this was the key. To confirm on your car, you can test pin 4 on the chassis side with a DVM. I also cleaned this connection, but the temperature still wasn't displaying.
Ultimately, I took out the cluster and tested continuity between the sensor and pin 26, confirming an internal problem. When I bench tested the gauge with a 12V battery across the pins, it worked fine. I then bypassed the SI board, added an extra washer to the grounding nut, and replaced the missing grounding nut (M4x0.7).
The combination of these actions resolved my issue. Since I couldn't find this information easily, I'm sharing my process here in hopes of helping someone else in the same situation.
Next, I examined the motor, particularly the sensors (about 3 of them) within the thermostat housing. I realized that the gauge sensor was the one with a single blade and a brown/white wire. Contrary to online suggestions pointing to other sensors, this was the key. To confirm on your car, you can test pin 4 on the chassis side with a DVM. I also cleaned this connection, but the temperature still wasn't displaying.
Ultimately, I took out the cluster and tested continuity between the sensor and pin 26, confirming an internal problem. When I bench tested the gauge with a 12V battery across the pins, it worked fine. I then bypassed the SI board, added an extra washer to the grounding nut, and replaced the missing grounding nut (M4x0.7).
The combination of these actions resolved my issue. Since I couldn't find this information easily, I'm sharing my process here in hopes of helping someone else in the same situation.
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