find the Original wire it should be in the main harness, if not you could use the temp sensor off the T stat and hook that up to a relay this is the way the OEM relay works.

 

I can only imagine the reason they bypassed the oem wiring in the first place is because the fans weren't coming on, and they couldn't figure it out. There would be no other reason to do this.

I think it might be easier at this point for me to wire up my own fuse and relay rather than trying to troubleshoot what was already there. I would just need some help with how to wire it. I already have a spare starter relay that I could use for it.

 

Ive seen this done alot, and theres never a good reason to do so. Fairly simple system most likely cause is a bad thermo sensor which is an easy fix

 

I'll see if perhaps I can trace the wire from the fuse box.

 

not necessary infact it may not even go to the fuse box (Pretty sure it goes to the fan relay), easiest method is to find someone with same model. look to see what portion of the wire harness it comes out from and match the color up, additionally if they did cut the wire hopefully that is the only wire that was cut

 

A lot of the wiring was cut up when they did the B swap. This isn't the first electrical issue I've had.

Also, I'm pretty sure there are zero '91 HF's left in Minnesota, at least that aren't in even worse shape than mine.

Ill see if I can't locate a schematic. Otherwise I'll either start probing wires or just invent my own wiring.

Whats the risk of not running a fuse or relay? That's how it's been for years with 2 fans and no problems.

 

Causing a short circuit burning up wiring and or causing a fire. Also if you mean hooking the fan up directly to battery without an activator thats not smart as the fan should only go on while needed this way there is less stress on the fan and your keeping your engine at optimal temp.

you can run a relay + a fuse using the temp sensor here you go this should be correct

 

Find the fan switch, unplug the fan switch, grab a paper clip, put the paper clip in the plug, turn the battery on. That will tell if its the relay or a short somewhere

 

Thanks for the schematic! This is awesome. I really think it's quicker to wire it myself rather than locate oem stuff, because everything has been tampered with and a lot of oem stuff doesn't work.

I picked up the relay, connectors, some 10ga wire and a 30a inline fuse today. Should be ready to go once the fan and radiator gets here.

 

yup thats a good method, your basically bypassing the temp sensor when you do this, if all relays and wiring is in order your fan should come on, If fans come on with this method but not at operating temp you have a bad temp sensor

 

What if I wanted to wire it up with a toggle switch that could override the temp switch to turn the fan on when I wanted?

So, anytime the switch is on, the fan is on regardless of ECT.

When the ECT hits 195 or whatever triggers it, then the fan would be on whether the toggle switch is on or off.

Doable?

 

Why don't you just buy a quality "thermoswitch" in the on off points that you are after, say on at 190F off at 180F and a "thermostat" that would agree with this switch, with say a 170F open point.
(I swear you guys were killing me with the improper thermo this and that terminology...)

 

you actually don't want a low temp thermostat Honda used the precise temp for a reason, too cold and you can damage bearings etc.

thermoswitch is not needed as you can adjust the temp your fans come on as needed with Hondata. I'm sure other ems has similar settings for this.

totally agree that the toggle switch is a terrible idea tho it's not practical at all and pretty much impossible to be monitoring temps while driving all the time

 

Yeah right now it is just a toggle switch, and I completely intend on wiring it back up to the (thermo, temp?) switch, whatever it's called.

Wiring the toggle in parallel to the thermo switch would serve the purpose of having a backup in case of a failed thermo switch, wiring problem, etc. But yeah otherwise I guess there should be no need. I just like having control over things.

 

lol I think you are worrying too much. They don't have high failure rates, and even so this is why we have temp gauges and there's also an alarm thru Hondata that will put the cel on when overheated.

my concern is that the fan will be on when it should not such as at highway speeds when natural airflow becomes superior to the fan and the fan has adverse effects.

 

Are the switch that turns the fan on and the sensor that sends the ECT to the ecu separate, or are they the same component? Can anyone post a pic or diagram of exactly which one controls the fan?

I am wondering because if I just wire up my own complete fan circuit, and wanted to just cut the wires to the fan switch to tie into, I don't want it to mess up my ECT signal to the ecu if it's the same sensor.

 

There are 3 sensors ECT, Fan control, and the one for gauge cluster.

The cluster signal is a single wire in the head near the vtec solenoid or dizzy
The ECT is a dual wire connector in the head near the vtec solenoid or dizzy
the fan control is a double wire connector in the thermostat housing

First pic is fan control sensor
second pic shows the Single pin gauge cluster sensor, and the one in the guys hand is the ECT sensor for the ecu

 

Perfect, thanks for all the help!

 

170 is not that cold and not cold enough to damage anything. That is actually the oem temperature for my honda bike.

 

Yah I don't completely disagree with that, however pretty sure Honda chose 180 for a reason

 

Emissions mainly. As well as keeping the Throttle body/ IACV/ FITV free of ice. Possibly aiding in burning off any condensation inside the engine. But like I said, Honda went with a 170F thermostat in their more performance oriented power sports products, so 170 would still be more than safe and warm enough, while further aiding in cooling and increasing knock threshold.

A 170F thermostat doesn't mean that your engine will always stay at 170 degrees, it just means that it cracks open at 170 and allows coolant to start flowing. It would probably be beneficial in your situation to get the coolant flowing a little earlier as well as the fans on a little earlier too. I think a 170F thermostat and 195/185 thermoswitch would be optimal, when paired with quality fans, that are being properly powered.

As far as your setup being safe, no, using the ignition power supply to power the fans is a bad idea. Now, if you had a relay and a separate power feed directly from the battery (fused) while using the ignition power source and that switch to signal the relay on and off, it would be safer and more efficient. Though you really should just get a schematic, figure the wiring out, ditch that wiring hack job /switch and set it back to factory (with upgraded radiator/fans and possibly upgrade thermostat/thermoswitch as well, depending on how well it cools).

 

Alrighty. I got the half rad mocked up, fits really nicely and hooks up in about 30 seconds.

However, I don’t think I’ll be able to fit a 12” puller fan with my wastegate. 12” is the full width of the radiator, and the wastegate is less than 1” away from it. I could maybe do a 10” puller and keep it offset to the side.

What would be the best option? 10” puller fan, or 12” pusher fan?

 

I would recomend the 12" SPAL pusher medium profile. Its what I use

Dont cheap out on the fan or youl be sorry you did

 

Oh yeah, I’m definitely getting a SPAL fan with the highest flow rating that I can. Everyone says a puller is better, but for the layout of my engine bay I think running a pusher will be ideal and hopefully still give me plenty of cooling capacity.

 

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I would still do the puller.

But go to the SPAL site and get the exact diagram measurements they provide and make va small card board mock up based upon those measurements. Then you'll know for sure