Yet another cooling fan question

darnell · 05-31-2006, 04:56 AM

Hi again everyone. I have searched the forum (really) and I have either missed the answers to my questions or didn't search the right topic. Here's my goal on my 87 Carrera. I want to add a switch on the cooling fan. Here's how I plan to do it. I want to run 10ga wire from the relay to a switch (preferably the foglight switch I'm not using) then to ground. Hopefully I'm on the right path. Here is what I need and some questions. I need a drawing or sketch showing exactly which relay. I need to verify that the pin I need to use is #87 and finally, how do I get the foglight switch out to wire into it? As a plus (maybe) I have deleted my stereo but it doesn't seem easy to get to the fog switch. Alternately, I have a switch formerly used for an alarm that is just sitting there in the dash. I thought of using this but should I be concerned about it's ability to handle the amps?

Thanks in advance for the help. I really want to get this done before the weekend.

Wil Ferch · 06:26 AM

Ok... we need to be "clear"....

You (maybe) want to do this for the front fender mounted oil cooler fan? Your text is not very clear on this. Some folks might think you're talking air fan on the engine at first.

I've done this. There are a number of ways to go. I don't have the capability to upload a wiring diagram, which would be the best, so I will try text.

You need to understand electrical circuitry. Pardon me if I'm wrong, but I'm not 100% certain that you do, based on your text. Doing something wrong electrically can be a big deal, so excuse my less-than Emily Post etiquette.

A relay "pin-out" is fairly generic. #30 and #87 are the end-points of a switch that opens/closes on the main power circuit. Try to visualize a knife-switch that has a handle on it so you can open/close it by hand ( you'll see where this is going later). The other pair of contacts....#86 and #85 are the end-points of an electromagnet that when energized.....act like your "hand on the lever" and close the contacts 30/87. So the 86/85 pairing is the "control" circuit and the 30/87 pairing is the "main power" circuit".

here's something that helps visualize a relay--> http://electronics.howstuffworks.com/relay1.htm

So now you know the various contact points on the relay.

I wired my system this way:

- at #2 ( 16A) fuse of my 10 fuse block on my 85 Carrera....took wire from the output ( bottom) and fed to #30 on relay. ( This is existing power from battery thru a 16A fuse). 1987 and 1985 Carrera's use similar (maybe even identical in this area...but CHECK) fuse boxes.
- fed wire from #87 to positive (+) connection on motor. Fed wire from other motor connection to ground.
- I decided to fuse the "control" circuit" and not JUST the power circuit as Porsche does stock for the 87+ cars. Found a wire from ignition switch to fuse #5 on my block. This has a common bridge to fuse positions 4, 5, 6. Number 4 is lowest amp fuse of these three ( 8A)....and I fed a wire from the output of #4 ( bottom) to my dash mounted switch ( Dorman model 643-224 that has an amber light)...connection #3 ( labelled "power" on the switch). Connection 1 (labelled "ground) on the switch went to ground. Connection 2 on the switch ( labelled "accessory") went to connection #86 on the relay. I fed a wire from relay #85 to ground.

Something along these lines may work for you too but you are advised to find a model-year specific wiring schematic for your car. Another point...the relay "pairings" are fairly generic, but are bi-directional. Pairing #30/#87 might be interchanged....and #86 /#85 might be interchanged. Doesn't matter.

Hope this helps.....draw it out..it'll help in the visualization.

Doing it "this" way...minimizes the "amp" draw on the switch. The switch is not "directly" part of the power circuit...as it seems you wanted to do. My switch only controls the relay's electromagnet...which is orders-of-magnitude less amp draw. The relay power contacts, then "act" as the switch. Most relays have a 30A rating..plenty for the fan and wiring.

- Wil

darnell · 05-31-2006, 06:21 AM

Wil,

Thank you. Yes, I am wanting to wire a switch into the oil cooler fan on my 1987. I remember last year simply running a wire from the relay (I believe pin 87 but don't remember) to ground and the fan ran always. I don't want to do that this year. Unfortunately, I've lost the schematics and don't even remember what relay I used. My assumptions (likely false) was to run the same circuit only wire it into a switch I am not using currently such as the foglight or the one for the old alarm.

Thanks,

MattAlpha · MattAlpha's Garage

If you still want to use your fog lamp switch in this circuit, it'll be a pain to get to it. It doesn't simply pull out of the dash into the seating compartment. You have to access the switch from the trunk after removing the blower fan and some associated ventilation hoses. A major pain unless you already have the motor taken out. The knob on the fog lamp switch unscrews from the switch and then you need to unscrew the mounting plate so that you can remove the fog lamp switch from the dash via the trunk access to it.

I hope this makes sense and helps,
Matt

Wil Ferch · 05-31-2006, 06:29 AM

The switch I used was located in the empty hole ( that we all have in our 911's)...where the rear wiper switch would normally be located. It's a square hole under the vinyl ( feel it with your finger !) between the left two gauges on the dash. The Dorman model 643-224 unit I used fit perfectly.

- Wil

darnell · 05-31-2006, 06:31 AM

Matt,

That helps. I means I'll be using the alarm switch.

Thanks

mthomas58 · 08:49 AM

I just completed wiring a manual LED rocker switch addition to the oil cooler fan in my 1987. Much information here on how to wire, but, I could not get my LED to work using the fan relay #85 pin to ground side method (not enough current to light LED). I was able to get everything working on the load side if the circuit so I thought I would post my results.

Used a three pronged Radio Shack LED Lighted Rocker Switch. Prongs for Line, Load and Ground. Wired as follows:

1) Line pin on Switch to Fan Relay Pin #30 (Common)

2) Load pin on Switch to Pos lead on fan using wire splice near the factory connector in trunk near the spare tire (power lead is black/ ground is brown)

3) Ground pin on Switch to ground on chassis.

Mounted switch next to Light switch on dash. Fan will work with ingition off since Pin 30 on the relay is hot not "switched". Pulled fan fuse to make sure the fan is protected and it did not work so all is well.

mthomas58 · 04-07-2007, 08:56 AM

Test wiring

Ultimate switch location

derkpitt · derkpitt's Garage

Mark, your not bypass the relay are you?

That's not a good idea.

If you want the led to just show that the sw is on, you can pickup power for it anywhere. Do not use the pwr side of the relay thru the sw.

mthomas58 · 04-08-2007, 04:15 PM

Quote:

Originally posted by derkpitt
Mark, your not bypass the relay are you?

No, I'm not bypassing the relay. Picked up power at the common pin #30 on the relay which is fuse protected. If I pull the oil cooler fuse, the switch does not work. I think I'm OK.

Thanks!

masraum · 04-08-2007, 06:19 PM

Yes, as in the original post, the easiest way is to gound the ground pin that flips the relay with a switch. Switch on grounds the relay and triggers the fan, switch off, open circuit and no fan.

Since you aren't working with the main power to the fan, but only the trigger circuit of the relay the amps are quite low.

fintstone · fintstone's Garage

Switching the relay ground is best (safe) because if you pinch the wire somehow and short it to ground...there is no fire. Your fan just stays on.

These links should have the info you need:

Pelican Link 1

Pelican Link 2