The PO had installed the union tee on my 81 Spider upside down so that the water temp sensor was facing up. It got continuously banged by the hood spring and was taped in place by him with mounds of tape. As part of my timing belt effort I replaced this Bosch connector when the union went back on (right side up). The wires to it were both white, so without thinking, I just connected the new connector and snapped it in place. Only later did it occur to me that this is not a switch, but a sensor (I think). So one wire goes to the electronic control unit and one to ground. I have a 50/50 chance that i got it right?
According to the wiring diagram they should have been red/green and black/violet. Maybe a PO also rewired it at some point, and further up the wiring bundle than I went I would find the two white wires spliced into the coloured ones. who knows?
Does it matter if the wiring is reversed? If so, I can figure out which lead goes to ground, but how can I know which connector on the sensor is the ground?
Will it cause damage if I start the car with the wiring reversed on that sensor?
Thanks in advance,
T
Help == Water Temp Sensor wiring reversed?
-
Luddite
Re: Help == Water Temp Sensor wiring reversed?
The coolant temp sensor for the 1981 is described in the wiring diagram as an grounded variable resistor. Pin 49 (black/violet) is grounded, and reversing the wires would effectively cause the sensor to appear as a short.
-
Tango
Re: Help == Water Temp Sensor wiring reversed?
That's what I was afraid of. Unwrapping my tape and shrink tubes and swapping the leads is no problem, but how do I figure out which lead is to be the ground?
I suppose I could unwrap the wiring bundle upstream until I get to wherever the splice is where the coloured wires begin, if ever, but if there is a way to tell at the switch which contact is the ground, that would be a lot more direct.
Then I could just see which wire has no resistance to ground, and I know that one is pin 49.
OR, there is a plastic ridge on the switch and matching groove on the connector (if I dont have that reversed). if someone can see which colour wire goes to the left or right side of that feature when the feature is oriented "up" or away from the osberver, that would work too...
On the other hand, does anyone know: from the output on the computer, the current will still pass through the sensor on its way to ground -- does a variable resistor device care which way the current goes through it? I didnt directly connect ground to the pin on the computer, it just might be running "backwards" across the sensor from the way it was before. 50/50 chance.
If this is a device that depends on the change in resistance due to temperature change being detected by a change in current, maybe it doesnt matter???
I'm just flailing around here to some extent. The lesson: trying to get one more thing done at 10pm is an error precursor situation.
I suppose I could unwrap the wiring bundle upstream until I get to wherever the splice is where the coloured wires begin, if ever, but if there is a way to tell at the switch which contact is the ground, that would be a lot more direct.
Then I could just see which wire has no resistance to ground, and I know that one is pin 49.
OR, there is a plastic ridge on the switch and matching groove on the connector (if I dont have that reversed). if someone can see which colour wire goes to the left or right side of that feature when the feature is oriented "up" or away from the osberver, that would work too...
On the other hand, does anyone know: from the output on the computer, the current will still pass through the sensor on its way to ground -- does a variable resistor device care which way the current goes through it? I didnt directly connect ground to the pin on the computer, it just might be running "backwards" across the sensor from the way it was before. 50/50 chance.
If this is a device that depends on the change in resistance due to temperature change being detected by a change in current, maybe it doesnt matter???
I'm just flailing around here to some extent. The lesson: trying to get one more thing done at 10pm is an error precursor situation.
-
Luddite
Re: Help == Water Temp Sensor wiring reversed?
The resistive element doesn't care which way current passes. But one connector is already grounded. If you ground the other connector, you've got a dead short. Wish I could help with the connector, but mine doesn't have the original wiring either.
Best way is to check continuity between the pins on the ECU connector and the sensor connector.
Best way is to check continuity between the pins on the ECU connector and the sensor connector.
-
Tango
Re: Help == Water Temp Sensor wiring reversed?
I dont think I can ground the wrong contact on the ECU. I think it will look like this rough sketch. the only thing is that current will flow backwards through the sensor.
I'm going out to see what clues I can find.
[Later]: Now I've gone up the wires and unwrapped electrical tape until they disappear into what I am pretty sure is original factory wiring bundle tubing and they are both white. I am concluding that it doesnt matter, that they are both white. I dont know why it doesnt match Artigue's schematic for colour, but it's down tools for a week anyway. On the road, but when I get back I should have the cooling system finished and the trial startup within a couple of days. Then we will know.
T
I'm going out to see what clues I can find.
[Later]: Now I've gone up the wires and unwrapped electrical tape until they disappear into what I am pretty sure is original factory wiring bundle tubing and they are both white. I am concluding that it doesnt matter, that they are both white. I dont know why it doesnt match Artigue's schematic for colour, but it's down tools for a week anyway. On the road, but when I get back I should have the cooling system finished and the trial startup within a couple of days. Then we will know.
T
-
Luddite
Re: Help == Water Temp Sensor wiring reversed?
The problem with the theory is that pin 5 (black violet) is separately grounded at the ECU. If you ground Pin 13 by connecting it to the grounded part of the sensor, the signal never gets to the sensor - it is shunted to ground.
-
Tango
Re: Help == Water Temp Sensor wiring reversed?
I just can't see the short.
In the left hand diagram, current would go from 13 on the ECU to 13 on the CTS, through the resistor, out 49 and then to ground.
In the right hand diagram, it goes from 13 to 49, through the resistor, out 13 on the CTS and then to ground.
In both cases, there is no direct path to ground. Or what am I missing?
T
In the left hand diagram, current would go from 13 on the ECU to 13 on the CTS, through the resistor, out 49 and then to ground.
In the right hand diagram, it goes from 13 to 49, through the resistor, out 13 on the CTS and then to ground.
In both cases, there is no direct path to ground. Or what am I missing?
T
-
spider2081
- Patron 2024
- Posts: 3015
- Joined: Fri Jan 27, 2006 11:45 pm
- Your car is a: 1981 Spider 2000
- Location: Wallingford,CT
Re: Help == Water Temp Sensor wiring reversed?
I Have a print for a 1981. Both the wires are white on this diagram.
Theory wise the thermistor in the "T" has a negative temperature coefficient. That means as the temperature goes up the resistance goes down. The fact that there are 2 wires connected to the sensor would lead me to believe the sensor connections make through these wires and not by its physical mounting in the "T"' The thermistor is in series between pins 13 and 5 of the ECU and it should not be affected by which direction it is connected.
If someone messed with the wires and has shorted pin 13 to ground the ECU would never think the car is running cold which is what the sensor is used for. It tell the ECU to make the mixture richer during cold warm-up time. Once normal operating temp is reached the mixture goes back to its regular rate. I don't know the resistance range of the thermistor.
The connector is keyed so I doubt it can be plugged in upside down.
Hope this is some help
Theory wise the thermistor in the "T" has a negative temperature coefficient. That means as the temperature goes up the resistance goes down. The fact that there are 2 wires connected to the sensor would lead me to believe the sensor connections make through these wires and not by its physical mounting in the "T"' The thermistor is in series between pins 13 and 5 of the ECU and it should not be affected by which direction it is connected.
If someone messed with the wires and has shorted pin 13 to ground the ECU would never think the car is running cold which is what the sensor is used for. It tell the ECU to make the mixture richer during cold warm-up time. Once normal operating temp is reached the mixture goes back to its regular rate. I don't know the resistance range of the thermistor.
The connector is keyed so I doubt it can be plugged in upside down.
Hope this is some help
-
Tango
Re: Help == Water Temp Sensor wiring reversed?
Aha! My diagram is Brad Artigues's which is based on a 1980 FI. The 81 wire colours are different, and mine match. It can't make a difference or they would have been pretty derelict in using the same colour. The way I understand a thermistor works means that the ECU runs a current through the resistor and measures either the voltage drop change or current as the resistance changes with temperature. So, I should be golden.
I know it worked fine before I spliced on the new connector because the PO had problems with the engine suddenly running rough and cutting out whenever he opened the hood. He didnt know why. It was because the hood spring kept tugging at this broken sensor connector most times when he lifted the hood and the mixture went rich. Plugs were darkish.
Thanks everyone. What a great resource this forum is!
Where can I get a copy of the 81 wiring diagram? Just in case for future reference.
I know it worked fine before I spliced on the new connector because the PO had problems with the engine suddenly running rough and cutting out whenever he opened the hood. He didnt know why. It was because the hood spring kept tugging at this broken sensor connector most times when he lifted the hood and the mixture went rich. Plugs were darkish.
Thanks everyone. What a great resource this forum is!
Where can I get a copy of the 81 wiring diagram? Just in case for future reference.
-
pooldoctorstl
Re: Help == Water Temp Sensor wiring reversed?
Tango - PM sent regarding the wiring diagram.
Jeff
Jeff
-
Tango
Re: Help == Water Temp Sensor wiring reversed?
Well, it started up fine tonight. Needed a battery boost after the winter, but started right up and ran fine. Even smoother after a few minutes. Also, and this is embarrassing, but keep in mind that I just bought the car in the fall and drove it very little before putting it away for the winter: there was a manual in the trunk the whole time entitled "Spider 2000 Electrical Diagnostic Manual 1908-1981". In that, both wires are white as on the car, so probably it was good either way.