I've been working out some of the wiring issues I had as a result of the flurry of activity that occurred while slamming my car together for the WCC 04. I didn't like my home made vacum form fan shroud and undersize (free) Saab fans. They worked ok but they LOOKED free...

I made a real nice aluminum shroud and installed two 14" street rod fans. That was the start of a whole rash of electrical back feed gremlins.

First I overloaded the thermo switch and burned it out which shut down the fans. I replaced it not thinking the added power drain from the larger fans was frying the switch. I burned the second switch in about 5 minuted.

Then I noticed when I pulled the headlight switch the volt gauge would drop to about 10.5 volts and the temp gauge (motor gauge, I have two, one on the motor and one on the radiator) would peg past 250 deg.

When I switched the lights off the gauges would return to normal. I moved the big power lead I had running up to the fans from the back of the fuse panel to the hot lead junction above the fuse panel.

That didn't help the gauges at all. When the volt gauge was reading 10.5 volts I tested the battery with the motor running. Volt metter showed 13.5 volts. That was a good sign.

I ran ground from the volt gauge in the console all the way back to the battery and cleaned (sanded and scraped )and added a star washer to the ground for the other gauges and that fixed the feed back problem.

OK, Back the the fans. I'm still burning fan switches. I want to add a relay like you do when wiring in some big running lights. I have a relay but I don't have a clue how to wire it.

There's a diagram and numbers on the relay body. The parts guy told me it's the same relay they sell for the remote car starters. So I thought that would be a good thing incase it ever burned I could get a replacement easy.

Here's the numbers they look like Bosch numbers.

85 86 87 87a 30

What goes where?

Should I have one relay per fan or will one relay run both fans?


One more update. I drove the car today for about 15 miles though the city without the fans. The car ran at 170 deg. I got into some stop and go traffic and the temp rose to 190 deg. I pulled over and clipped on my jumper wire in place of the burned temp switch. About 4 blocks later the temp was at 180 deg. I jumped on the freeway with the fan jumper still connected and the temp. went to 160 deg. on the radiator gauge and 162 deg. on the motor gauge. Once I get the fan switch relay thing figured out I should have a good cooling system.

Oh, and one more thought on the fan thing. I thought I may install one temp switch on the block to run one fan. And one switch on the radiator like I have now. This way I would start cooling the water when the motor calls for it not when the radiator calls for it. I'm not sure there would much advantage to this as both front and rear gauges seem to show very close to the same reading.

I run a wire all the way from the battery to the relay for the fans on all the V8 conversion cars.

Also: run two relays. One for each fan and trigger the ground to the relays with your thermo switch (make it hot all the time and turn on the ground side) The hot should be fused and coming from the battery.

B

Ya, ok, Thanks "B", I'll do the power wire from the battery thing.

Do you also go directly from the battery with the ground also?

Or is the chassis ok for that?

I made the positive wire to the thermo switch mistake already.... Works for home wiring.... Duh

Now what wires go to what numbers on the relay?

85 86 87 87a 30

What goes where?

Run 12V positive to 30 and 86
run a wire from 87 to your fan
and from your thermo, to 85
Your thermo should be ground switching.
Its been awhile since I did this but that should work

Thanks for the info but I'm still a little confused. I want to do this correctly. What connects to 87a? How does the relay ground the thermo switch?

Ok, when you hook up the thermo switch, one side goes to ground, when it reaches the set temp, it makes contact and passes the ground to the relay which makes the relay engage, Nothing gets hooked up to the center terminal on the relay. I just pulled the sheet I got with my radiator setup, its a little different than I used to wire up relays when I would do them. If you follow this, it will work. Here is a diagram of what you want to do. I hope this helps.

30 and 87A are connected when the relay is triggered, and it doesnt matter if 85 and 86 are reversed, it still does the same funtion(trigger the relay). So it doesnt matter which way you wire the positive wires. If you hook it to the ignition 12v the fans will shut off when you turn off the engine. If the car is hot and you wire it to non switched 12v the fans will continue to run after the car is shut off and continue to cool the radiator and will shut off when the temp goes below the thermostat temp setting. If you have a good strong battery, that would be the way I would go. Its up to you.

OK, I started working on installing the relay using Scott's diagram. I need to get some 10 GA wire and as "B" reccomended I'm going to install one relay per fan.

I'm studying the diagram and don't understand the ignition wire. I have a question.

Q.) If I run the car until the thermo switch grounds the fans and then turn the key off before the temp drops will the key turn off the relay and stop the fans?

I haven't completed the wiring so I haven't tested it out. I don't want to run a bunch of wire and then have to re-run things.

Thanks for putting up with my questions. Wiring is always a challange.

I think I know the answer, maybe someone else will chime in.

If you make the 10 GA wire hot all the time the fans will continue to run, if you make the 10 GA wire hot with the key the fans will shut down when you turn the key off.

That is correct, I am going to wire mine hot all the time so the fans will continue to cool the radiator after I shut off the car. I am going to run a big strong battery to make sure it wont run it down enough to kill the battery. It should shut off when it cools down, If I run into problems I will put a switch on it to turn it off manually or on manually as needed.

Scott, what is up in that diagram? It looks like you are wiring the fans directly to the battery, and then using the relay to control the ground??? Is that correct? Is there a particular reason to put the relay on the ground side rather than the power side??


Rich, a relay is an electrically-operated electrical switch. The Bosch relays with the terminal numbers 30, 85, 86, 87, 87a work like this:

When there is no voltage across 85/86, a spring inside the relay will connect 30 to 87a. When there is voltage across 85/86, then the relay will connect 30 to 87. (Note that it doesn't appear to matter which of 85 or 86 gets ground and which gets ~+12V; as long as one does have voltage and the other has ground the relay will trip and connect #30 to #87.)

Generally, the relays are set up so that battery power goes the #30. #87a is usually not connected to anything (you might want to tape it up so nothing shorts to it), and #87 is used as the "output"--it goes to whatever you are powering; in this case the fan(s).

So the typical wiring is: Battery (to fuse, within 18" of wire run from the battery!) to pin #30 on the relay. Pin #87 to the fan. Pin #85 to a "switched power" source. Pin #86 to the thermo switch. (This assumes that the thermo-switch provides no connection when cold and provides a ground when it is warmed up.)

--DD

Scott did say the diagram was not the way he runs the relay normally. This electrical stuff is cool and confusing.

Nice observation Dave, the diagram was written by Rod Simpson and that is how he has been wiring them for many years. As for the relay, yes, it is triggered by the thermostat when it reaches temperature. The 12v coming from the battery goes through a circuit breaker instead of a fuse so that it will reset itself in the event of a short rather than to have to replace a fuse all the time. I used to wire alarm systems for power window and door lock triggers the same way and remote starter systems in cars. In order to activate the relay, you need a power and a ground, you would never run 12v positive through a thermostat so it has to be the way it is in the diagram. Its much safer to run the ground from a switch to the relay and fans in case it shorts out. Worst case there would be the fans dont shut off and your battery goes dead. Better than starting a fire. If you use the relay to trigger 12v positive to the fans, you would need a seperate circuit breaker for each one and 3 relays instead of one. Wiring it the way in the diagram, you only need one relay and one circuit breaker. If you use a switch to trigger the relay, then when the switch is off, the fans will not run, if you just put a jumper across from 30 to 86 then it will run anytime the temperature is above the setting of the thermostat. I thought the diagram was quite efficient. Could you elaborate on what you see as a problem with it?

My bosch guru friend from Clevland showed up at my door this morning. We went for about a 15 min drive. Left the car idle and changed drivers, came home and left the car idle for about 5 minutes in the driveway while we played with the fuel mixture. (NO FANS!)

My car runs so cool I may not even bother with a fan at all. I could drive non stop without a fan if I didn't get caught in traffic too long. Even then 3 or 4 stop lights don't seem to be too big of a problem.

We don't need no stinkin relays!

Problem? Nope. I was simply confused by it.

You don't need three relays if you switch the positive side, though. You use the ground from the thermo-switch to supply one of the "triggering" signals, and you use power from the ignition switch to supply the other of the "triggering" signals. That way when the ignition is on and the thermo-switch is closed ("hot enough") the relay's "input" gets connected to its "output" and you get power going to the fans. You can use one large relay and mount both fans in parallel, no problemo.

If the above is how Simpson has been doing it for years, I won't argue. But I still don't see the particular point of having the fans wired direct to the battery and having the relay on the ground side.

--DD

A very informative thread.........I'll earmark it for reference. In the meantime, here's a site with a lot of very good info (though nothing specifically on fans). Security systems and general info has some interesting reading.

http://www.the12volt.com/installbay/default.asp

Andy

Rich,

My Renegade radiator came assembled with fans installed and all wiring ready to connect (+/- wires). It has a single relay and positive wire is connected directly to battery with 30A fuse for protection. Negative side is attached to chassis. Being somewhat electrically challenged myself, I opted for this plug and play setup.

Red Optima battery is mounted in front trunk making connections about as easy as it gets. System has been in service for about 2 years now without any problems. I use a 100 amp alternator. The fans will run for 1-2 minutes after engine is turned off but has not caused any starting problems. In addition to the normal accessories (lights, stereo, etc.), I also run a/c with a "switched" fan in front of condensor. This one is relay protected as well.

Spinning my 10.5:1 compression engine over after running a/c for over a hour, fans running for a couple of minutes after key is turned off, there appears to be the same amount of juice to spin starter as noted by the rate engine turns over in this situation.

I would not omit the fans since you already have them mounted. It will be just a matter of time before you get caught in traffic.

It appears you have enough info here to wire the relay properly. If you need additional info/pics, let me know.

John

Thanks for all the great suggestions. I'm just kidding about canning the fans. But my car is really running cool. I'm very happy with the "Howe" radiator I used. I'm thinking the outboard tubing may be helping with the cooling. I put 30+ miles on today. I went to Menards to pick up some 10 GA. wire for the power lead to the fans. I drove through town with no fan wiring. the front and rear gauges sat at 170 deg. and only went to 180 deg. for about 4 blocks after I was caught at a couple of lights.

I was remembering one of the conversations I had with one of you guy's at the WCC 04. Sorry I don't recall who it was. I spoke with so many people. Forgive me for not extending credit where credit is due. Anyway, someone suggested adding a light to the fan cuircut so you would know when they turned on and off.

Anyone ever do this? and how did you wire it in?

I run a fan "status" light on mine as indicated by the green lens on attached image. Bought it at Radio Shack for about $2.

Wiring was simple. Find a hot wire (12volt) at fans or wiring supplying 12v to fan that is energized only when fans are running (should be terminal 87 on the above sketch). Jumper across your thermo switch to determine what is hot and when to be sure. Run a wire from that source to your new fan status light (red wire). The black wire from fan status light can be connected to any ground at gage cluster (brown wire). Or, a new ground can be made by securing to chassis.

The red wire on my instrument cluster is a idiot light for high water temperature. It is connnected to my VDO dual water sender unit, mounted on intake of engine.

All total, 4 cooling system indicators. Two gages with senders in different locations on engine, one idiot light for high temp. and the fan status light. My fans are activated by a thermo switch mounted at top of radiator. This piece turns fans on at about 179F.

With the fan status light installed, you should notice fans will not activate while in cruise mode above 45 mph. While in traffic and fans activated, you should see fans turn off once returning to cruise mode in about 1-2 minutes. This can vary depending on how much heat your engine makes and of course the efficiency of your cooling system.

The fan status light is simple to install and can be your first indicator a cooling system problem is present. If you have a problem (slow leak, head gasket, trapped air, etc.), it will let you know before the small change in temperature gage readings. As you spend more time behind the wheel with status light installed, you will become accustomed to what is normal.

One more thought. A true test of the cooling system should be performed in summer weather (temps. at or above 90F). Spend more than 20-30 minutes/miles during your trial runs. I like to log 100 miles for a true test. The engine/cooling system would be more properly tested if you mix up the driving conditions (city/highway driving) and with longer durations. As you learn the cooling system and how it responds with the measuring devices you have installed, be prepared to see change when the ambient temp. drops by 10 degrees or more : )

Checking my system a few days ago, I saw 170F while on the interstate running 80 mph for extended periods using a 180F Mr. Gasket high flow thermostat. Outside temp. was 92F and I was running a/c the whole time. Fans would come on only when operating in town, below 45 mph and while at red lights (temp. in this mode varies around 180F). Fans turn off above 45mph and about 2 minutes after returning to cruise mode. I would not be alarmed if temperature readings were at or around 220 if extended time was spent in traffic. I call "trouble" anything above 225F or a large fluctuation in temperature (180-225) in a short time.........I call this spiking and can have many contributors.

John

Attached is thermo switch used to trigger fans. This piece is screwed into radiator. Note on and off temperature settings etched on unit as prescribed by Renegade Hybrids.

Various water senders I have used. I prefer the unit in center of pic since it provides source for gage and idiot light. Also note depth of probe. Depending on where your sender is installed, I feel this one provides a more accurate reading with sender submerged deeper in water.