I've been led to believe this is the sensor that controls the fan, it's an OBD0 B18A, which doesn't have a knock sensor. My fan doesn't switch on, and i can't see a plug that would have connected here, can anyone quickly describe to me what route that plug would normally take back to the fuse box, so i can crawl under my car and look to figure out where the wires were routed? There is a switch in my dash, but it doesn't control the fan, and i can't find where the wires pop out into the bay.
Any help much appreciated, I thought this might belong in tech, but I figured the guys doing tucks and repinning stuff would know the wire routes better.

 

It is a fan control switch. You did not share (as you are supposed to) the year/make/model chassis that this engine is installed into, so I cannot give you specific wire colors for your application. However, I am going to take a guess and suspect that you have a '99-91 civic, which would have two individual wires with clear/milky colored barrel connectors at each end... one wire is black and the other is yellow/green. There may be a large black rubber cover encasing the two barrel connectors, although most have gotten pretty rotten after 25 years. Simply find a round two wire donor plug that fits the sensor you have pictured... and graft it to the two wires that I have described.

If you have a fan switch sensor mounted on the thermostat housing, you can also connect your two original wires to that location as well. These would be found on '92+ Civics and '94+ Integras, but could have been installed on your engine. Posting a pic of your thermostat housing would help me to be more specific... and a picture of what you have pictured already including the sensor that is just under the intake manifold and slightly right of the sensor you have pictured... this may also be a fan control switch wired up already (it looks like one of the two clear barrel connectors is plugged in, but I can only see the very edge of it).

 

My apologies for neglecting to post the car haha. It's an 89 Civic, I thought it might be irrelevant because I'm still not certain what harness was used to do the swap. It's a DX as well.
Does the information you gave me still apply to your knowledge? And if so which fuse box do those wires come from? I'm sure I'll have no problem sourcing a plug, and wiring it. I've done that before, it's just that I'm not sure about the routing.
Also I'm familiar with the other plug on the thermostat housing, I did look briefly and feel for it, don't think I have it. It was briefly though, I may have been too hasty.

 

Also I can look for that other sensor and take a pic in the morning, thank you for checking it out.

 

I figured instead of starting a new thread, I'd ask this here, because it's in the same vein and might be an easier way of solving the problems that past hackjobs have caused. (I've found several shoddy splices with wires that don't have corresponding colors, as well as a few free hanging pins.) I was thinking of just buying a whole harness and p74 from an OBD1 LS Integra, and just routing that when I pull the engine to build it. I know I'd have to swap injectors, alternators, and distributors, as well as removing the resistor box that was installed, but is there anything else I'm missing from the B18A to B18B? I think the only plug I'd have to depin and remove would be the knock sensor from the newer LS, and I'd possibly have to move the fan switch from the back of the block, to the thermostat housing, like we've been discussing.
What say you sir?

 

Your '89 Civic fits the bill with the explanation I provided above. With the exception of the '92-95 Civic platform, it is always best to start with the original engine harness that came with the car and MODIFY it to fit the new replacement engine. In the case of a dual point fuel injection system being converted to a multi-point fuel injection system, there are MANY ways to do this, so you have to rely on the harness modifications that currently exist on your engine and chassis harness. In the original engine harness, the black wire terminates at the main ground bundle that bolts to the thermostat housing and the yellow/green wire goes to the driver's side harness plug junction near the injector resistor box. The wires do not go to any fuse box.

 

I'll definitely take your word for it, but can you elaborate on this a little more? It was my understanding that the harnesses would be similar enough, that the only issues I'd have would be the plugs I mentioned, maybe lengthening a few wires because ground points between the two cars may have been placed differently, but that still isn't much less than people go through for an MPFI swap. I'll add that my intentions were to do this when the engine bay was empty. Maybe you're considering that pulling the old harness out and routing the new one with the engine still in the bay would be an exercise in futility, which I fully recognize.

 

Oh, and I didn't thank you for the help.

 

You trade one set of unknowns for another. With the original engine and chassis harness, you know what goes where because it works already. So you can simply shorten or lengthen any of these plugs or clips and change those as necessary. Distilled down, a different engine may need additional wiring, so all you have to do is add those wires between the sensor and the ecu plugs. If you change the engine harness, you will find that some plugs that join at the shock towers are different... and even those that seemingly do plug in, the wiring sequencing is not necessarily congruent. This means that wires at sensor plug "A" on the engine may not terminate at the proper location at the ECU plugs... so introducing these variables only compounds the difficulty of what you are trying to do.

Here is a practical example: Your EF sedan has only two fuel injectors on the engine and thus, two injector clips on the original engine harness. The Integra engine harness has four fuel injectors on it and thus, will have two additional injector ground wires that plug into the chassis harness at the shock towers. Now, between the passenger side shock tower and the ECU, your EF sedan only has two wires in it for fuel injectors... which split to turn into 4 wires just inches before the ECU. So how would your two additional wires actually work if you simply plugged in the Integra harness into your car ???

Oh, and your welcome.

 

10/10 explanation, would read again.
Pretty unfortunate that I'm beyond a clean slate, but no big deal. Okay. Well, I'm off for the next three days, I'll tear into more of the wiring and report more findings/fixes.

 

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