Fan switch

[Curt C.]

OK, please realize I have little understanding of electricity. Here is the problem. I have the Flex-a-lite fan with thermostat. I also have an override switch. When the car is running at temp with the override switch off, one of the ignition wires gets hot as hell. When the overide switch is flipped on, the wire cools back down. Whats going on here? I can tell that this wire burned out and has been replaced before. Something is causing an overload. Maybe a better question is: what is the proper way to wire this set-up? Do I need a relay?

[Bud Man]

Most of the time, the switch is the weakest component of the circuit.

On any heavy draw component like a fan, I would very strongly recommend installing a quality relay ( stay away from Lucas), and see what happens.

Bud

[Bruce Edwards]

Curt,

You do not give much to go on. How is the fan wired? What wire is getting hot the main feed or the switching wire? What gauge is the wire?
Like to help out but need a bit more to go on.

Bruce Edwads
Gemini Motorcars Inc.

[Curt C.]

Sorry Bruce but I have not crawled under there to see whats up and what the exact wires are. This is a Classic Roadster so one of those guys should have the diagram and be able to tell me how to wire. I just noticed that a wire coming out of the steering column (ignition) was getting hot as described above. The wire has been replaced and the number is no longer there. I will thoroughly review the wiring and report back with a diagram.

[Bruce Edwards]

Curt,

So the main feed wire for the car is getting hot? Install a 30 amp relay. It sounds like someone wired the fan straight to a source like the fuse box and the load is to high for the wire size. Find the wire that feeds the fan now and use that one for the feed to the relay. Take another wire from a battery sorce and hook it on to the feed side for the fan. Hook the fan feed wire to the relay so when it comes on the battery feed will juice it. Ground the other realy terminal that is the mate for the feed from the car i.e the one that now turns on the relay.
This will take the load off the harness and put it on the battery and the larger cables that can take the load.
Easy!

Then again I have been doing this for 20 something years.

Bruce Edwards
Gemini Motorcars Inc.

[dscott]

The original Classic harness used wire # 151 for fan ignition feed. This wire went to a Black Magic fan switch which had a built in relay. If you have this wire supplying power to the fan it will melt or burn. You could be trying to draw up to 30 amps on a 16 guage wire. Use a universal relay and wire it as follows.
On the bottom of the relay it is numbered 30,85,86,87.

Run a 12 gauge wire from # 30 to the fan +. Ground the - side of the fan to the chassis.

Run a 12 gauge wire to # 87 from the battery or the firewall circuit breaker.

Run wire # 151 from the Classic harness to #85 on the relay.

Terminal # 86 will run to a fan temp sender on the engine (you will need to buy one). Jegs or Summit can supply this.

If you want an over ride switch on the dash then run a wire from # 86 to the switch or use # 157 from the Classic harness.

On the dash over ride switch you will have wire # 161 and # 157. Remove wire #161 from the switch and tape the end, it won't be used. Run a ground wire to the switch terminal that wire # 161 was on.

Terminal # 86 is the ground for the fan circuit, the temp sender and the switch both supply a ground when either the stated temp is reached or you turn on the switch.
Don

[Art Burtt]

I mounted the relay down on the frame near the side of the radiator and then followed Don's instructions to the over ride switch. It works fine and no over heating wires.

[Jack21]

Problem solved. Always put high amperage accessories on their own separate power leads. 30Amp realays should suply the power from the battery to the accessory, and should have a 20 or 30 amp breaker (instead of a fuse) on it. Only the control side of the relay is controlled or switched. Fans, halogen headlights, horns, CD ignitions, sterio amplifiers need relay operated circuits. Minimum of 12 ga wire on power circuits.

Another headache saver if installed during the initial build is redundant grounds. Redundant grounds use the chassis frame only as a backup (redundant) ground. Although these can be made easily, Ron Francis wire works (wire-works.com) makes a ground strap that connects all ground leads directly to the battery ground. I used one on the engine side of the firewall, and a second behind it on the dash side of the firewall. All component grounds terminated on one of these two busses, which was wired directly to the battery ground. A frame to bus connection was also added.

If you've ever been driven nuts trying to diagnose intermittent grounds, or corroded grounds on steel bodied cars, you'll appreciate the simplicity and reliability of a redundant ground system.

[Curt C.]

Don, Two questions: (1) Could one just replace wire 151 with a piece of 12 gauge? (2) The balck magic fan has its own thermostat. It also has a connection for "Manual" overide. Do I still need the temp sender? If not needed, what changes to the relay wiring need to be made?

Thanks for all the replies guys. Looks like I will be getting this sorted out rather quickly

[dscott]

Curt, I haven't used the Black Magic fan in about 12 years so I don't remember how they were hooked up. I quit using them because they couldn't keep the car cool. It won't help to replace just the wire that gets hot, It runs to the fuse block and the ignition circuit. I would either replace the fan with one from Spal, add the relay circuit that they sell or use the fan you have and wire it in with a relay and temp sender.
Don

[Curt C.]

The fans control box has four connectors +, -, M (manaul overide) and C for air conditioning on. As I stated the fan has its own internal thermostat. If I hook the relay up as detailed above, it will provide juice to the fan when the engine temp sender kicks in, but the fan itself will not kick on until the internal thermostat kicks on. However, I bet if I switch the power connection from + to M, it would work and bypass the internal thermostat. Or... Instead of running 86 to a temp sender / switch, I could just ground it and rely on the fan T-stat which does work. The manual overide, which is just a switched hot wire, is already hooked up. Will one, if not both of these alternative work??

On another note, my fan (Black Magic) keeps the car plenty cool with a 380 RWHP 351W and I live in Las Vegas. However, I do have a custom four core Griffin radiator in place of the one supplied with the kit.

[Double Venom]

Curt,
What Don is saying, is the black magic fan turned out to be very unreliable. The built in thermostat would vary by 20 to 50 degrees constantly. We simply removed the litle "4-pin" connector box you describe, wiring it directly to a 180 degree sending unit mounted in the intake water flow.

You asked, the answers are here.

DV..PS...the "BM" fan is one of the most AMP abusive fans on the market, at least the old ones.

[Curt C.]

Got it! I am getting the Autometer temp sender and wiring per Dons instructions. Thanks

[Jack21]

Don't confuse apples with oranges.

The Temperature sender provided by Autometer is the temp sender for your temp gauge. It does not get wired to your fan circuit.

The second temperature sender is for the cooling fan. Some fan thermostats monitor hot air as it exits the fan shroud. I prefer a t-stat that monitors the water in the block. More accurate. In my case, I drilled and tapped a second t-stat fitting in the intake right over the water jacket outlet in the head. This is a Ron Francis Wire Works fan t-stat kit.

And if both Don, and DV are expressing second thoughts over your choice of fans, I'd heed their advice. Easier to swap fans now than after car is on street (and overheating). I'm using a 16" Scotts which works fine. They swear by Spal and could give you a good price on one. The "Mutha" of the fan install is mounting the rad bracket to the frame, mounting the fan bracket to the rad, and mounting the fan to the fan bracket so it just clears the steering rack on the bottom, and just clears the hood bracket on top in the hood down position. You only want to do this once.

Theory of operation. Bat power (directly from the battery through a separate fuse or circuit breaker) goes to the control relay, then out to the fan motor on the NO (normally open) relay terminal. The fan motor can be grounded to the frame, or grounded to a grounding bar which is grounded to the battery (per previous description).

A splice on the ignition wire is then routed to the control lead on the fan relay. The only power being used on this control circuit is the magnetic coil inside the relay. The rest of the fan control is called "complete the ground".

The relay coil is energized when the magnetic coil inside the relay being powered by the ignition circuiit is grounded to the chassis or engine. This ground is completed through the fan thermostat sender. The fan sender is Normally Open sitting on the bench. When the water temperature reaches 205 deg., the contacts inside the sender close, completing the ground to the engine block, and powers on the fan from the relay. When the water temperature drops down to 180 deg, the contacts inside the sender open, the relay then opens, and the fan turns off. A fan override switch on the dash provides an alternate means of completing the ground aside from the temperature sender. A second wire can be run from the temperature sender terminal on the relay to a switch on the dash. The other terminal on the dash switch gets connected to a chassis ground. Closing or turning on the switch on the dash completes the ground, and powers on the fan from the relay.

Control relay systems like this are used when high amperage devices are being controlled by low amperage control circuits. Cooling fan is one example. Halogen headlights, high energy ignition systems, sterio amplifiers, horn, and starter are others.

[Curt C.]

Thanks Jack, but Autometer does in fact make a temp sender for its warining lites (part # 3246). The one I ordered comes on between 190 and 200. I will look into the Spal. The BM has kept the car cool since 1992. It may be suspect though due to its age.

[jwinkler]

I went through this (and solved it with this group's help ) a few years ago.

Apparently the thread that I started to ask for help is now archived, but the key is to wire in the relay like Don says so that not only are you using proper gauge wire, but you're also no longer pulling all the fan power through your fuse box. Before I rewired my fan, I blew the first ignition switch, and subsequently melted the fuse that was added when the ignition problem was fixed.

I guess a fan just doesn't have to run as much in North Dakota as it does in Texas or Nevada - it's the only reason I can think of for using such a small gauge wire - I think I rewired mine with 10 gauge for the power circuit to the fan.

I can't access archives now, but if I can find it, it will be a good supplement to get you through this.

One thing that helped me was having a multi-meter (I'm also an electrical systems neophyte) - I was able to test continuity and function for the wires and switches I needed to use, and also understand what exactly a relay does.

Good luck - once you locate all the places you need to connect the wires, it will go quickly!

JLW