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1991 Corolla AE92 4AF
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Discussion Starter · #1 · (Edited)
Hey everyone:)
I have a 1991 Corolla with 4AF carburettor engine. I have a problem where the fan doesn't turn on unless the fan switch (which is located near the thermostat) is unplugged. I thought that the problem was the fan switch, but today I was working on something unrelated and bumped a wire (pictured) next to the battery and the fan randomly started up. On looking closer, the box that the wires go into (pictured) is quite corroded making a dodgy connection. Clearly there is a problem here. Does anyone know what this thing is or how I could fix it (it looks like the insides of it are beyond repair)?
I am highly confused as to what this thing does.
Thanks in advance.
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1991 Corolla DLX 4AFE, 1994 Camry LE 5SFE, 1995 Avalon XLS 1MZFE, 2004 Sienna XLE/LTD, 2011 Camry LE
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You’ve mentioned components whose locations cover the entirety of your engine bay, and have also posted a highly zoomed-in picture of a single connector. Not sure what you’re trying to accomplish.
 

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1991 Corolla AE92 4AF
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Discussion Starter · #3 ·
You’ve mentioned components whose locations cover the entirety of your engine bay, and have also posted a highly zoomed-in picture of a single connector. Not sure what you’re trying to accomplish.
The components all happen to be on the same fan circuit. I am not an auto electrician, but I do have enough knowledge to know that this means that they all work together to get the fan turning despite the fact that they are not right next to each other.

As for the picture: I explained exactly where in the engine bay it is and I could take more pictures if necessary. I was hoping that someone would have had some experience with the problem that I am having.

As for what I am trying to accomplish: I am trying to find if anyone has had this problem and could give me advice on how to fix it based on their experience. If I bypassed the connector, the fan would run constantly, even when the engine is cold.
 

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The switch that turns your fan on if your coolant temperature is getting high is a coolant temperature switch. I don't have information on where that switch is on a Corolla 4A-F engine, but on a Celica 4A-FE engine, that switch is at the bottom of the radiator. If you disconnect the wiring harness from that coolant temperature switch, the fan should turn on at high speed. If your coolant hasn't reached that elevated temperature, the switch will not open, causing the fan to turn on. In normal driving, the fan will not turn on as the car is moving and has air going through the radiator cooling the coolant. If the car is parked with the engine running, there is no air going through the radiator to cool the coolant, so it is normal after idling while parked for 10-20 minutes for the fan to start cycling on & off. If yours does this, you don't have a problem to solve.
 

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1991 Corolla AE92 4AF
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Discussion Starter · #5 ·
The switch that turns your fan on if your coolant temperature is getting high is a coolant temperature switch. I don't have information on where that switch is on a Corolla 4A-F engine, but on a Celica 4A-FE engine, that switch is at the bottom of the radiator. If you disconnect the wiring harness from that coolant temperature switch, the fan should turn on at high speed. If your coolant hasn't reached that elevated temperature, the switch will not open, causing the fan to turn on. In normal driving, the fan will not turn on as the car is moving and has air going through the radiator cooling the coolant. If the car is parked with the engine running, there is no air going through the radiator to cool the coolant, so it is normal after idling while parked for 10-20 minutes for the fan to start cycling on & off. If yours does this, you don't have a problem to solve.
Thanks for the reply.
My fan never turns on unless the harness is unplugged from the fan switch (even on a 40*C day in heavy traffic), so I am pretty sure there is a problem somewhere.
I am quite confused as to why the fan turns on when that pictured connecter is wiggled (even when the engine is cold and not running). Thus, I am thinking that there is a wiring problem there. The fan is always on if I bypass the connector (which is badly corroded), so I am not sure what could be done about that.
 

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My fan never turns on unless the harness is unplugged from the fan switch (even on a 40*C day in heavy traffic),
Does your coolant temperature gauge ever start climbing in a situation like this? You might want to leave your engine idling while parked and watch both your fan and your coolant temperature gauge. If the coolant temperature gauge begins to climb above it's normal operating temperature without the fan kicking on, then you will have confirmed the fan issue. If the fan kicks on after 15-20 minutes without the temperature gauge moving above its normal operating temperature, then the fan control is working normally.

It looks to me that your wiring harness connector has a protective cover over it (if that wiring harness connector is not used on your particular car). But that said, if you move it and the fan turns on and off rapidly, I would agree that moving the wiring harness may be causing it and that you have some kind of wiring issue there. What are the colors of the wires on that connector? Include the color of the stripes on the casings of the wires if they have any stripes on them.
 

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Does your coolant temperature gauge ever start climbing in a situation like this? You might want to leave your engine idling while parked and watch both your fan and your coolant temperature gauge. If the coolant temperature gauge begins to climb above it's normal operating temperature without the fan kicking on, then you will have confirmed the fan issue. If the fan kicks on after 15-20 minutes without the temperature gauge moving above its normal operating temperature, then the fan control is working normally.

It looks to me that your wiring harness connector has a protective cover over it (if that wiring harness connector is not used on your particular car). But that said, if you move it and the fan turns on and off rapidly, I would agree that moving the wiring harness may be causing it and that you have some kind of wiring issue there. What are the colors of the wires on that connector? Include the color of the stripes on the casings of the wires if they have any stripes on them.
Only way to fix electrical is with schematic, who knows if this is factory.or add on. Schematic will allow you to trace and troubleshoot.in logical manner. I am degreed electronics tech, never touch any wiring without schematic on old cars. Most are not 100% factory stock. That will make troubleshooting harder. If stock schematic will identify all parts for you..electrical can be tricky, impossible without diaghram.
 

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^^^^
I don't know if repairs without a schematic are impossible, I seem to remember solving a couple of electrical problems using a test light, a multimeter, and logic.
OTOH, a schematic can make things quicker and easier.
 

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1991 Corolla AE92 4AF
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Discussion Starter · #9 ·
Thanks for the advice. I idled the car for a while today and the fan did turn on eventually, so I don't seem to have a problem there. I had never heard it turn on before, so I mistakenly thought it wasn't working.
I think the plug that makes the fan start up is probably for the air-conditioned spec models (the fan is always on when the air-conditioner is on, as far as I know). I don't have an air-conditioner in this car, so I think the corrosion in the plug is making allowing the wires to make contact, which turns the fan on.
The advice is much appreciated :)
 

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Great. Does the plug (cap) have metal terminals on it? If yes, it may be a jumper plug (meaning when it is plugged in, you are jumpering the wiring terminals which keeps the fans in an OFF state. If you pull the plug out, you are creating an open circuit in that wiring harness which turns the fans on. If this is the case, you should clean the terminals on the plug and spray an electric contract cleaner on the connectors on the wiring harness connector side and (If possible) squeeze those connectors in the harness to close the gaps a little (puts more pressure on the cap terminals). That may help resolve the problem you might have with corrosion in there.
 
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