This is about the fan relays. I decided to set it up so that the ECU turns on the cooling fan. This meant changing pretty much everything because the old tube thermostatic switches were wired to ground pin 86 on the relays to trigger them. The ecu supplies a 12V signal, so now I ground the relays and power pin 85 to turn them on. Also, the AC/fan relay was wired so it pin 86 was grounded when the AC is turned on.

Here is the goal: 1. Have the ECU turn the low speed fan on. 2. Have the AC cycle the low speed fan on. 3. Have a manual over ride for turning the fan on. 4. Simplify the wiring. 4. EVentually encorporate a circuit, (Ed already posted this one) for keeping the fan on for one cycle after shut down. Never built it.

AT this point I have left the high speed relay as it was since I have only one programable output left on the fender mounted relay box for MSII. I could add another I think with an external wire run through the firewall from the ECU to the relay box. But I will put that off. So just assume we are currently working with two relays one for the AC and one for the ECU trigger. The high speed one has its own separate circuit now.

I wired the ECU/relay trigger by grounding pin 86 and running the trigger wire to pin 85. The supply 12v is to pin 30 and the output is on pin 87. That works as needed, (except at this point the on-temp does not agree with the actual coolant temp). Matt is working on that one with me.

I wired the AC/relay trigger by grounding pin 86, and putting a jumper wire from the clutch engage wire to pin 85 of a separate relay. I ran wires from pin 30 on the ECU/fan relay pin 30 of the AC/fan relay, and a wire from pin 87 of the ECU/fan relay to pin 87 of the AC/fan relay. When the AC clutch gets power, the relay for that effectively jumpers pin 30 and 87 for the ECU/fan relay.

So now I want to add a manual toggle to turn the fans on that does not also turn on the AC or send voltage back into the ECU. I could add another relay and have wire that in parallel with the existing ones. But I am thinking there is a way to do this to keeps the number of wires to a minimum. I think there is probably an elegant way to do this.

If I have a single12+ wire come out of the passenger compartment to pin number 85 on the ECU/fan relay, that would turn the fan on, but would feed back 12 volts to the ECU relay connection. Big damage might ensue. So one way to deal with this might be to put a diode in the signal line from the ECU. But being an electronics dolt, I know not what to buy, or how to orient it. I don't want to discover I have made a mistake with the smoke test.

And here is another goal: I would like to get a light on the console or dash that tells me when the fan is running, with a minimum of wiring. Everyone who looks at this car shakes their head at the number of wires now. I am hiding many of the wires now, but they are still there nagging at me. I got this idea from Brian Mimken who has such a light on his dash. I certainly see the value in having it. A could run a single small gauge wire from the power wire for the fan into the cabin and light a small incandescent bulb. Brian's is an LED which looks nice. I guess I could use the same single wire to power a LED, but doesn't that have to be a circuit with a load on it?. I apologize for all the words. I couldn't help myself. Help I am tying and can't stop!

Sam

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Use one relay. Put a diode in each trigger wire (+ relay coil feed) and have each and every feed activate the one relay. The diodes will keep power from feeding from any one trigger input back to the other inputs.

For the "Fan Running" light you'll need to bring in a wire from the output side of the relay. If you're using an LED you'll need a resistor too. If you really want it to be a "Fan Running" and not "Fan Relay On" you'll need to build a current shunt into the fan's power feed and use an op-amp to drive the LED.

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Joshua

Electrically smart people make my head hurt!

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I have been running mine that way for several years now.....can't imagine not having it that way. Looks nice and neat, one lighted switch to arm the system, fan light in the middle and the right side is the manual over ride switch. It is nice to know when the fan is running since it is hard to hear sometimes. All three switch panels are in a row and glued together.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I think I understand. What size resistor and diode? I'll chew on that for awhile. Helps pass the time when bored. Thanks much.

Sam

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The resistor will be specific to the LED you use. Choose an LED and then we can spec the resistor. Many LEDs meant for panel mounting have the resistor built in. This one looks easy.

The diode is just a plain rectifier diode like 1N4001, nothing fancy. The band on the diode will be towards the relay.

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Joshua

Radio Shack offers a 12vdc LED, with the resistor built in. It would be up to you as far as mounting/trim for it.

Roger

Thanks guys! The mounting part is easy. I understand that. I will go to radio shack tomorrow. Even though it works now, it is always nice to remove some wires, and I have the panels that cover the wiring removed for painting.

Sam

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OK. It is done. And all works. However,I did NOT unhook the ECU fan trigger and turn the fan on with the other triggers turned on to check the orientation of the diods on them. So if one of them is wrong, I suppose I may have done damage already. Howver, i think all is cool. But I AM paranoid.

I am going to unhook the lead from the ecu when I get home and turn on the fan manually and put a vom on the ecu trigger lead to see if there is voltage at that end. If there is, then I hope it did no harm yet. The band on the diod is pointing towards the relay, and there are no triigers connected between the Ecu and the diode. I have it covered now with heat shrink, so cannot visually verify now.

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If the band on the diode in the ECU trigger wire is towards the relay you should be fine. If the diode is backwards on the other triggers they won't work and you will feed power up that wire when the relay is activated. It sounds like you've got it all handled though.

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Joshua

The original title said it all. Geniuses did step up. I ran my test and all is fine. Took the Dart to a cruise tonight and although it never got up to the user specified temp of 195 to turn the fan on, when I got back home, I lowered the setting to 180 and the fan came on.

The logic was to think of the manual switch as the primary fan relay trigger. The AC and ECU trigger wires with correctly oriented diodes, were both spliced into that wire. This really cleaned up the fan relay area under the hood. Thanks for the great advice. Now I will look up Ed's circuit for making the fan run for one cycle after shutting down if needed.

Thanks again. Sam

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