Ok so another engine fan won’t turn on issue. I have tested the fan with direct power and it runs. I have grounded the fan switch connected and I hear the relay click but the fan won’t turn on. I have 12v to the 20a fuse with key on. What is my next spot to test, the relay?

 

Yes, the relay 'click' should send power out. Is it doing that?

 

The red wire, which is the fusible link should have 12v at all times, is that correct? And the Brown wire which is the 20a fuse wire should have 12v with ign on? I check the relay itself with another known good relay and that is not the issue. I tested the red wire and dont have 12v there at all, which is the fusible link wire I believe.

 

So I checked the 3 fusible links at the starter for voltage both before and after the in line fuses and all 3 have 12+volts with key off. 20a fuse has 12v with key on.

To recap, I ground the green/white wire for the fan switch and get the relay to click but no fan operation. swapped out with known good relay with same result. No power to the fan connector itself, but have 12v at all 3 fusible links with key off. Only have 12v with key on at relay, but no constant power at the relay. Fan motor was tested with direct battery power and ground and works fine.

 

check for 12V at fan side of relay when it is engaged. check continuity from fan side of relay to fan.

 

Are you referring to the 20amp fuse up by the fan or the main fan relay next to the fuel pump relay? Shouldn't the red wire at the main Relay have 12volts all the time, even with ignition off?

 

The problem has to be with the main power feed to the relay. The Red wire that goes into the relay has no power when it should have constant 12v power. I have power at the Brown wire aka 20a fused wire with ignition on. How exactly is the fusible red wire supposed to be run to the fan relay? Can I just run a new fusible link from the starter to the relay?

 

All the relay is, is an electrically operated switch, that allows some small switch somewhere (ECM, fan sw, etc.) to control FAR more power than it could by itself. When energized it connects the 2 big fat wires together. IIRC they're red (12V) and blk w red stripe (to the motor). LOOK AT the connector in any case: there's 2 small wires (the coil, that turns it on) and 2 fat ones (the contacts, the thing that gets turned on).

Meaning, when the relay is clicked, you should see 12V on both the red wire and the other. If it's there, then the problem is further downstream somewhere. Since there's not a whole lot of "somewhere" in that circuit, doesn't leave many other things to check.

 

Based on the wiring diagrams for the fan relay, it appears that the fusible link which I am assuming comes directly from the starter/battery goes to the relay and has constant 12v. Is this correct? That Constant 12v power line should feed the Black/red wire going to the fan. The only power i have to the relay is the smaller brown wire that gets 12v with key on. I am assuming because I don't have the 12v constant power from the starter ie fusible link, that is the reason i have no power to the fan when the fan switch is grounded.

 

Have you run a continuity check from starter lug to fan relay?

Details of the car would help us help you assume less things.

 

The car is a 305tbi 1990 RS. Stock setup that I know of.
At the start lug, the 3 fusible link wires all seem to have 12 volts, both before and after the in line fuse.

Is there a direct wire from the relay to the starter lug is my main question.

All of the other power lines coming off the battery lug have 12v power, ie all the fusible links. The 20a fuse up by the fan has 12v power in and out. The only line that doesn't seem to have power is the power line going to the relay. I am guessing that there is a break in the wire somewhere from the battery side through the wire loom to the relay. It would require me removing all the wires in the loom. Am I correct in my thinking at this point?

 

Looks like "Fusible Link E" (at battery junction block) > Red wire to relay socket. Should have power all the time. Switched side of socket > Black/Red wire, to fan motor.

 

So I should just be able to run a new 20a fused wire from the battery lug or hot lug on starter to the hot terminal on the fan relay and it should operate as intended.

 

You should be able to.

Or you could locate the open and repair it.

 

Ok, so I tested my theory about just running a new hot wire from the battery lug to the relay and my theory was confirmed. There must be a break along the wire between the battery side and relay. Biggest issue with tracing it is that half of the wire loom is behind the motor and consists of a large number of wires. I dont like the idea of having a bad wire somewhere but the amount of work to separate all the wires and pull the loom from behind the motor is no easy task. I will likely end up just running a new fusible link as this point.

 

Yes.

Sure. Hack it up. Put a hack job on it. Yeah that's always the right thing to do. 20A isn't large enough. Hack job. HACK. HACK. Is that what you are? Is there anything I'm leaving out?

OK, now that we've got that out of the way...

First thing to do now is, verify that there's 12V at the red wire bringing power TO the relay, WHEN THE RELAY IS OPERATED AND FULLY CONNECTED. Reason for that stipulation is, if there's a bad connection somewhere in that wire (*cough* fusible link end *cough*) and you measure it with no load, it's entirely possible that with a high-impedance measuring device such as a DMM, that it will report that 12V is present, if there's no other load; butt then, when the REAL load gets applied, the current has to flow through abuncha green copper oxidation or elephant snot or whatever to get where is has to go, and you might find, ... .005 V or some such on that wire. In which case, since there's NOTHING between the fusible link and the relay except for that big red wire and the connector where it plugs into the relay, there are only EXACTLY TWO places where the fault can be. Either at the fusible link, or at the relay connector. LOGIC dictates this and it is beyond question. (assuming of course that the wiring is still factory and doesn't already have a HACK JOB in it somewhere, of the sort you propose to add) The wire itself has a quantum-mechanical probability (many MANY zeroes between the decimal point and the first non-zero digit) of failing. Not quite zero probability, butt in The Real World, might as well be. Which means you don't have to worry about looms and "no easy" and all that other juvenile whining. Should be less than child's play to zero in on which end of the wire the fault is at.

Above all, DO NOT apply a HACK JOB to your car. Find the problem and repair it properly. Then your car will be JUST LIKE NEW again, instead of HACKED all to hell and failing randomly and unpredictably when you are least able to deal with it.

 

A little aggressive but I get it and as I stated, I do not want to do some half *** job which is why I am trying to properly diagnose the problem instead of just wiring a switch to the fan like so many people do. I wanted to know exactly how the circuit worked and determine where the problem is, which I have done. I cant say for certain the harness was not hacked up at some point either, I got the car cheap with it missing many components including the engine wiring harness and have been slowly piecing it back together. I have tested voltage at both the fusible link end and relay end, there is voltage at the fusible link end but not the relay end, ie there must be some break or impedance somewhere along the wire between the 2 points.

 

When you say "end", exactly what do you mean?

Physically, the whole thing consists of the terminal at the end of the FL that hooks to the batt, then the FL itself, then a connection where the FL is attached to the wire, then the wire, then a terminal crimped onto the end of the wire, and last, that terminal plugs onto a mating terminal of the relay. At each of those connections - ring terminal to FL, FL to wire, wire to relay connector, connector to terminal - there is a possibility that there's a break or corrosion or whatever. You can probe the wire with a sewing needle or something, and see if the actual red wire has 12V on it right behind the FL connection; then again just before the relay connection. If the 12V disappears within the wire itself, then that wire may have been hacked on.

Remember also, if it's "not easy" for YOU to get to it and inspect it, then it's ALSO "not easy" for somebody else to get in there and hack on it. Not saying of course, that it hasn't happened; only, that the usual reason people hack on stuff like that, is because they think it's somehow "easier" to do that, than to DO IT RIGHT. In which case, it's more likely that IF in fact it's been hacked on, it's somewhere easy to get to, and not down in an inaccessible harness somewhere. I'd save checking for that until all other options have been exhausted. Again, NOT saying it "hasn't been" hacked; only, if it's "not easy", it's not as likely. "Likely" is a term that kinda describes what you should and shouldn't expect to find wrong. See my signature for why thinking about that is helpful.

Check this thread for a schematic you may also find useful. Not sure it fits your car exactly butt it's at least very similar. https://www.thirdgen.org/forums/cool...fan-won-t.html Note that the red wire is 3mm; that's just a shade smaller than 12 gauge, and the FL is .5mm which is about 20 gauge. FLs are usually 4 gauges smaller (larger gauge #) than the wire they protect; therefore since that one is 8 gauges smaller, it's that much more likely to be blown by an overload. If I were the guessing kind, I'd bet that you'll find that there's not actually 12V on the actual red wire itself, even if there is on the opposite end of that FL, because the FL is bad.

 

I have tested the fusible links at the starter terminal and have 12v.
I have tested the lug that comes off the battery for hot wires and have 12v there.
I have probed the 3 fusible links between the fuse aka plastic housing on the wire and relay, on the passenger side of the motor and have 12v there.
I probed the red wire at the relay itself and that’s where there is no power.

this leads me to believe the issue is somewhere between the passenger side where I have 12v and the relay side where there is no power.

 

OK:

Now probe where it MATTERS.

What's on the lug doesn't matter; if there wasn't 12V there your post wouldn't be about "fan doesn't work", it would be about "car is completely dead". Since that's not what you're asking about, we already KNOW there's 12V there. IOW there's no information in that "test".

There aren't "3 fusible links" in the fan circuit, therefore that's irrelevant. The ONLY ONE that matters is the one that feeds the fan relay. What's on the other 2 wherever you tested them (you don't say which end, or what) doesn't matter. There's no information in that, either.

There's no such thing. A fusible link is a piece of wire, sized such that it will melt (aka "fuse") when the current in it exceeds the safe level for the wire it protects. Remember, it's NOT a "fuse", in the sense that it's protecting against whatever the LOAD is, developing a fault; it is ONLY intended to protect THE WIRE. The FL itself melts to keep THE WIRE (the Big Red one in this case) from catching fire. That's really all it's there for, is to keep the car from burning to the ground in case that wire gets pinched or chafed or something. It is NOT designed to protect against a fault in the motor, in the manner that the fuses in your fuse box are designed to protect against faults in the devices they supply power to. There is no "fuse" of that sort anywhere in the fan circuit. The "plastic housing", if you're talking about the round clearish or black thing about an inch long and 3/8" diameter with the FL coming out of one end and the Big Red Wire out of the other, is merely the cover for the connection (splice) where the FL is spliced onto the end of the wire it protects. If your FL needed to be replaced you'd cut all that off of the very end of the Big Red Wire, throw it all away, and crimp the NEW FL's splice onto the end of the Big Red Wire.

Get yourself a sewing needle and poke it through the wire insulation at each of the points I describe, while everything is completely hooked up, and the relay is clicked. Making sure that you're testing under those conditions is VERY IMPORTANT. "Testing" with the circuit disconnected or not operating can easily give you a "false positive" reading, such that your "test" makes it LOOK LIKE there's power there, when in fact, there ISN'T enough to work the fan motor. Therefore we want to measure the circuit WHILE IT'S OPERATING AND UNDER LOAD. Reason being, a connection can be "good enough" that if there's NO load, a DMM or the like, which is only a VERY TINY load (on the order of a millionth of an amp), can "see" 12V; butt the connection can be NOT "good enough" to allow LOAD CURRENT (tens of amps) to flow through it. Kinda like, testing a faucet for water pressure when it's turned off, and there's a restriction in the pipe feeding it that's so tiny that only a few molecules of water at a time can squeeze through: you might put a pressure gauge on it and the gauge show pressure, butt when you open the faucet, it might only drip one drop every 5 seconds. Hardly enough to wash your hands. Electricity works EXACTLY the same way. In which case, there will be 12V on one side of the bad connection, butt 0V on the other side, WHEN IT'S UNDER FULL LOAD.

Is there 12V INSIDE the fusible link RIGHT AFTER the ring terminal? There can't be 12V any farther along if it doesn't make it into the FL.

Is there 12V INSIDE the fusible link RIGHT BEFORE the splice connecting it onto the Big Red Wire? There can't be 12V any farther along if it doesn't make it all the way through the FL.

If you probed inside that splice during the time when everything is connected and the relay is operated and the fan SHOULD be running, and there's 12V there, then the FL is good, and you can skip the 2 previous tests. There IS information in that test, IF AND ONLY IF, everything was connected, and the relay was calling for the fan to run. Now the next thing you need to know is, does the 12V successfully flow through the splice and into the Big Red Wire when it's under load, since that's one of the points that there can be a bad connection.

Is there 12V INSIDE the Big Red Wire right behind the FL? There can't be 12V in the rest of the wire if it's not there right after it passes through the FL and the connection from the FL to the wire. This one RIGHT HERE is the main one that's untested as of yet.

Is there 12V INSIDE the Big Red Wire right before the connector at the relay? See above.

Is there 12V on the relay connector that's crimped onto the wire?

As you work your way LOGICALLY along the circuit while it's fully connected and under load (i.e. at a time that the fan motor should be running), you'll find 12V somewhere, then no 12V anymore where there should be 12V. The fault is then somewhere between those 2 points.

 

Thank you, I will go through those procedures.

 

Let us know what you find at each spot. Might help somebody else in the future, esp if what you find seems to be a likely common failure point.

 

Maybe this will help turn the light bulb on. replace the light bulb, with your fan. Now you can see why you need to measure 12V on both side of the relay.

 

Often times, when a wire or wire/connector interface is compromised, you can simply pull on the wire around that area, firmly. The wire, or connection, being broken (or corroded through) already, will separate, and stretch the insulation. The insulation will "hourglass" slightly where the break is being pulled apart...it'll be obvious. Easy Button way to find broken wires or connections.