I've been slowly replacing old worn out sensors and other parts. I currently have the 305 TPI under the hood. When I was replacing the distributor and wires I came across a connector that is not plugged into anything and I can't figure out where it belongs.

Also between the 8 and 6 spark plug I broke off a connector to what looks like a sensor but I'm not sure exactly what it is. I've attached photos of both.

Any help identifying these plugs/sensor would be greatly appreciated. Thank you.

 

That sensor by the spark plugs would be a coolant temp sensor. I think that would be for the secondary cooling fan. Other connector I can't place, but someone will probably know it.

 

Wire colors would help.

 

If the "other connector" has pink/blk and blk/wht wires, it's probably the legendary "mystery connector".

It doesn't go to anything. Best guess is, since those wires are power to everything ECM-related under the hood (pink/blk) and ground (blk/wht), it was how the factory could hook up an entire engine and ECM and all its parts, for testing at the motor plant, before a stillborn motor electronics package got shipped to an assembly plant to be put into a car.

 

I will check the wire colors and let you all know. Seems odd GM would leave a connector in the engine wiring that's not needed or used.

 

You weren't paying attention.

It's not odd at all. Very common practice in manufacturing actually; especially electronics, but also much simpler things, like ... cars.

It WAS both needed AND used. Just not in the final build of the car.

 

The "sensor" between plugs 6 and 8 is the fan switch for the secondary fan. It looks similar to the knock sensor and uses the same type of connector. Either replace the connector by splicing on a new pigtail, or just slide the existing pin back into the switch as it is, and it will continue to work fine.

 

Nevermind found my answer. Appears to be the knock sensor.

Anyone know what sensor this is and if it has anything to do with the electric fans? It's located on the passenger side just above the the K member.

 

That bottom sensor is your knock sensor.


The top sensor tucked by the manifold is the switch for a secondary fan on TPI motors. Guessing you also have the singe fan?


My 87 came prewired with the secondary fan switch but there is no second fan. So the wire literally just ends at the fan connection junction close to the front of the frame rail.

 

I have the electric dual fans which I'm currently trying to figure why they don't turn on. I've replaced the relays and the fan switch.

 

Primary on the passenger side turns on with the ECM. at around... 235?? i wanna say. The secondary driver fan comes on when the switch in the head closes at... 240???? Its pretty high.
On 87 I think only the passenger side comes on for ac


"Also between the 8 and 6 spark plug I broke off a connector to what looks like a sensor but I'm not sure exactly what it is. I've attached photos of both." "I've replaced the relays and the fan switch."

What did you replace for your fan switch? That sensor you're asking about by the manifold is the secondary fan switch. if you replaced the switch in the driver side head then that is the gauge sender. The 2 pin sensor in the intake manifold below the thermostat next to the cold start injector is for the ecm.... I think that's how it calculates when to turn on the priamry fan by grounding the ground wire.... . Secondary fan is grounded by the mechanical switch in the head though ( the switch by the exhaust manifold in question that is black...it looks old / dirty so i dont think you replaced the correct one....)

You'll need to fix / reconnect that wire you broke off... just spice a new connector on. they're pretty cheap / widely available and are identical to the knock sensor connector... btw, you should reconnect your knock sensor!

 

I only unplugged the knock sensor for the picture.
I replaced the sensor that is between the 6 and 8 spark plugs. I replaced it with the hawks 180 degree fan sensor switch.
I've already replaced the temp sensor for the gauge cluster

 

I've heard quire a few people say the 180 sensors are defective / burn out easily...


I dont know where the ecm grounds the first fan, but try ground the wire for the seond fan.


With the ignition on, the fan should come on when grounded since the fan gets constant power when the key is on. If it comes on the switch you got is defective... if not theres issues elsewhere

 

I did attach a multi meter to the switch and when I grounded it the fan turned on. Are you saying the switch is bad or is there a bad ground in the wires?

 

if you're grounding the wire that leads to the switch and the fan comes on, and the fan doesnt come on when the switch is connected (assuming you're letting the engine come up to the correct operating temp) then the switch is likely faulty or got too much build up / sealant on the threads that's preventing the switch from grounding properly since it grounds through the engine block

 

I bet it's the sealant on the switch. Im gonna remove it tomorrow and see what happens. I will let you know if that was or wasnt the issue.

 

let us know!!

 

The 2 prong wire looks like egr.

 

The 2 wire plug looks to possibly be for the mat sensor under the plenum.
There is a short harness that connects the mat sensor to that 2 wire connector.