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Discussion Starter #1
Hi folks,

I recall some years ago seeing a post on how to rewire the fans (on an S4) that adds a relay to avoid powering the fans through the ignition switch. I've tried searching 7 ways from Sunday and can't find it.

I think I figured out how to do it but would be nice to sanity check.

Does anyone have a link to that post?
 

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But Mad North-Northwest
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Which fans: radiator fans, heater fan, or AC fan?

Radiator fans should already be on a relay.
 

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Discussion Starter #3
I'm interested in the radiator fans. There's an AC fan?

I do see a fan relay but the hot side that is connected to the fan through the existing relay contacts is routed through the ignition switch. I wanted to have power go directly to the fans via a separate relay that is energized by the existing fan relay contacts. I thought I recall others say this was a good idea and seems like one to me too.

Thanks,

Hector
 

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But Mad North-Northwest
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The AC blower fan is what I meant. Under the glovebox. The radiator fans do dual service for the radiator and AC condensor.

I know the relay trigger is ignition powered, not sure about the hot side. Doesn't really make sense to have a relay if you're just going to power the hot side through the switch, but this is Alfa so who knows. Let me take a look at the wiring diagrams tonight.
 

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The ignition switch provides the power to energize the relay which then powers the fans, it does not power the fans directly. So what you seem to want to accomplish is the way the system is originally designed.

Perhaps you are thinking of a starter relay?
 

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But Mad North-Northwest
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I think that's an older revision of the wiring diagram. The one I have shows pin 30 coming from the battery and pin 86 coming from switched power (which makes a hell of a lot more sense). I can post a pic later.
 

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Discussion Starter #8
Paul, my diagram doesn't show what you describe because pin 30 of the relay that goes to power the fans makes its way eventually to the switch (2nd connector on the left of the switch, pin 1), not the battery nor firewall junction block.

It sounds like Tom knows of an updated diagram that works the way we want. What I wonder though is if the latter diagram Tom is looking at reflects the way they did it in the model years after mine and maybe differs from how mine is wired (my manual is Rev Feb 1990 - from CarDisc). I haven't verified that my car actually matches the above wiring yet.

Hope you guys are right - less work for me!
 

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Hector - I see what you mean now. Your diagram shows the relay control connected to the hot section of the buss and the power for the fans coming from the switched section. All I can say is that doesn't make much sense from an electrical perspective. I don't own an S4 but I do own a couple of 164's and I can tell you that the wiring diagrams are full of errors, some corrected by later revisions and service bulletins others corrected by owners.

If you can't find a revision that makes sense you may have to actually physically verify this which doesn't look like it would be too difficult to do.
 

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But Mad North-Northwest
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Yeah, there are a lot of errors in the wiring diagrams. I've got a printed paper version that has many of them corrected. The original diagram you have makes zero sense from a wiring standpoint.

Corrected diagram is below. I verified on my '91 that the integrated fuse at the relay has +12 with ignition off, so this drawing appears to be correct.
 

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Yes that makes much more sense, exactly the opposite of what is shown in the first diagram posted. I suspect it was a printing error.
 

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Hector: I made the relay change that you are talking about. I had problems with the fuse in the fan relay getting hot when the fans were on. I even replaced the fused relay with a new homemade one with the fuse externally mounted so that it would cool better. I wound up using one relay for each cooling fan to split the load. Look up the headlight relay modification in the search engine, it's basically the same setup. I powered the relays from the terminal block behind the air cleaner on the driver's side fender. Other people on this board have had the same problem I had with the fused relay melting.
 

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Discussion Starter #13
Thanks very much Tom for going the extra mile with that information, really appreciate it. What is the rev date on your diagram just out of curiosity?

Bob, that's interesting - do you know if your S3 fan is wired the same as the S4s? I guess that fuse is there regardless so maybe this is worthwhile mod. What was the problem with that fuse getting hot - that it could blow or that it would reduce current flow to the fans too much?

Thanks,

Hector
 

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No, the s3 ans s4 are wired differently, the s4 has 2 electric fans and the s3 has a belt driven fan. It's been quite a while since I disassembled the s3 and I didn't pay that close of attention to that detail. I'm sure someone with a s3 could be more accurate about that. The s4 fan relay has a 15 amp fuse embedded in the relay case. Over time it would slowly melt the plastic that the fuse is constructed out of. It did the same thing to both of my relays. Someone posted a picture of a melted fuse sometime earlier this year. The 2 fans must have been pulling 14.99 amps, not enough to blow the fuse, but enough to heat up and slowly melt the plastic and eventually blow the fuse. After the first failure I disassembled the fans, checked the brushes, cleaned the armatures, and oiled the bushings. I guess the fans in some s4's just draw more current than others. My VOM meter will only read up to 10 amps DC, so I don't know the actual current that they were drawing. There were no stray resistance reading to ground from the fan relay output with the fans disconnected. When the fans kicked on I could reach under the dash to the fuse panel and literally feel the fuse heating up.
 

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But Mad North-Northwest
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Just to clarify it's a 30A fuse in the relay on an S4.

I've heard of them melting but when I pulled my fuse yesterday the terminals looked fine. It's quite possible that oxidation builds up on the contacts over time which could cause overheating and melting.
 

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Discussion Starter #17
Well this is shocking (pun intended)...I pulled the fan relay and found that connector #30 didn't have +12v until the key was turned on. This actually matches my diagram! I guess they corrected this in later cars.

I'm going to go ahead and put the relays in for the fan and the headlights.
 

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But Mad North-Northwest
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Hmm...not sure what to tell you. I'm definitely seeing ignition-off voltage on Pin 30.

The only thing I can think of is that there was a TSB issued for '90-'91 Spiders to rewire the fusebox to switch the power source for the relay *trigger*, but I don't think that did anything to pin 30. I did this years ago and had forgotten about it: TSB 40.90.04

I can pretty much guarantee that the wiring diagram you posted is not right for your car. If it were you'd have all the fan voltage going through fuse 8 and that sucker would blow. But no idea what the actual wiring looks like.
 

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...I can pretty much guarantee that the wiring diagram you posted is not right for your car. If it were you'd have all the fan voltage going through fuse 8 and that sucker would blow. But no idea what the actual wiring looks like.
I agree as the first drawing depicts the circuit as having a 40A and a 15A fuse in series which makes absolutely no sense. There is no way that a circuit could have been erroneously designed like that, it has to be a drawing error.

The question is, did the drawing error exist prior to production and did some vehicles actually get wired that way on the assembly line? That seems like a possibility although it was never intended to be as such.

If so I think the solution is to wire it exactly as shown in the second drawing. There is no need to add extra relays or a patch circuit, just wire it as it was originally supposed to be.
 
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