Mystery wire (1 Viewer)
- Thread starter Jakey77
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
That wire goes to a temp sensor in a small bracket hanging down off the exhaust manifold near cylinder 4 or 5, which I can see is present in the last photo. The carb fan is only supposed to come on after you turn the truck off and only if the engine bay temp is high enough.
A quick test is to ground that wire to the body, turn the key to “on”, then to “off”. Carb fan should come
On if the motor brushes are good and it has 12V. Check for 12V at the electrical connector to the fan - one probe from your meter to a clean unpainted part of the body (or a bolt head) and then test the contacts in the connector with the other probe. Maybe that connector only has one contact, I can’t recall.
A quick test is to ground that wire to the body, turn the key to “on”, then to “off”. Carb fan should come
On if the motor brushes are good and it has 12V. Check for 12V at the electrical connector to the fan - one probe from your meter to a clean unpainted part of the body (or a bolt head) and then test the contacts in the connector with the other probe. Maybe that connector only has one contact, I can’t recall.
- Thread starter
- #3
Thanks! So that temp sensor is connected in some way/communicates with the carb fan? Carb fan definitely not coming on. Just not sure if this wire is related or not.
The temp sensor is a thermistor: a simple temperature-dependent resistor. The bracket is grounded through the engine to the body (or should be), so the thermistor is the ground path. As it heats up the resistance goes low and provides a path to ground for the 12V that’s present at the fan - the fan comes on. As things cool down the resistance rises and eventually the fan turns off because the electricity isn’t able to flow to ground.
Try the tests I mentioned above. You need to see if you even have 12V at the fan first. Also check the proper fuse. The factory service manuals will have the details on which one that is.
- Thread starter
- #5
Awesome …I’ll test and report back
.
i have been mending various wires and this was in front of me and this is what happend after i correct ID'd it as the Carb / EFI manifold Fan Thermistor Wire also
.
- Thread starter
- #7
That’s hilarious…I’m sure this is my problem. Just funny I’m like “what’s that wire for?” As I’m trying to fix my fan
- Thread starter
- #8
In my situation the wire to the temp sensor is connected to the sensor but not the carb fan…are you saying take the wire when it is connected to fan…disconnect from sensor and then ground it? If so I’m not sure where this wire is suppose to connect to the fan
That wire should go to the wiring harness on the inner fender, and through there to the connector for the fan.
To test, I plug the ground wire from the thermistor (temp sensor) and ground it out. Turn the truck on, then off. Fan should come on.
Are you saying the ground/sensor wire fell out of the connector?
- Thread starter
- #10
Yes the wire is just dangling off the temp sensor…
- Thread starter
- #11
Ok…just watched a video and figured out the ground wire situation. The plug the ground wire is green up top by the carb. I thought it was the plug coming off the fan. Anyways …I touched the broken wire coming out of the green plug by the carb to ground and viola…fan runs!
So now that I’ve diagnosed that…this wire needs to go to the thermocouple on the manifold?
I believe so. Where is the thermistor’s wire currently going?
Also, the entire wiring diagram is in the back of the Body & Chassis FSM. Top of the page, click the Resources tab, narrow down to 60s. All the manuals are there.
- Thread starter
- #13
Ok…thermocouple wire is just dangling. I’m assuming it goes to the broken ground wire but not sure as it’s been repaired before and is different color wire …I’ll try tomorrow
- Thread starter
- #14
Ok ..all fixed. The ground wire is coming off the green plug up by the carburetor. It’s not coming directly off the fan plug. When I touch that ground wire to frame fan came on I splice a new wire onto that and attached it to the thermal coupler on the manifold. Drove around for a while to get the truck up the temperature and Walla the fan comes on thanks for all your help everybody. I tried to upload a video of all this, but apparently mud doesn’t allow videos.
I just looked at my 60 and yes, the thermistor wire comes into the harness at the same place the fuel control solenoid wires do. That’s the green plug on the carb, so I followed those wires back to the inner fender and that’s right where the thermistor wire joins. It must feed through the harness for a couple inches and then go to the plug at the fan. Nice work.
- Thread starter
- #16
Man, thanks for the help. Easy fix after some research. Pretty cool design with the thermoresistor. Those fans do what they are suppose to…I was getting vapor lock on hot Oklahoma days. No more looking like an idiot when my “cool” truck won’t start.
The fan really works on the carbureted trucks!
