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'86 honda civic si fan wiring


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geezrx 
Member - Posts: 19
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Joined: May 08, 2014
Location: Oklahoma, United States
Posted: May 09, 2014 at 8:39 PM / IP Logged  
Vehicle has electric fan with thermo sensor control in bottom of radiator. I want to install an illuminated switch to manually overide this sensor when desired. The switch I want to use is a rear defroster switch from the same model car as seen in the picture below
'86 honda civic si fan wiring -- posted image.
I know from trial that I can simply jumper one wire of the thermo sensor to terminal B & one to terminal D on the switch and it will allow bypass as desired...however, as I am "electrically challenged" I'm concerned that this would not be the correct/safe way to accomplish this. Below is the circuit schematic from the Honda Electrical Troubleshooting Manual for my vehicle
'86 honda civic si fan wiring -- posted image.
Taking into effect that I struggle with schematic diagrams, could someone detail a correct and safe wiring plan to implement the above switch into this circuit on my non-air conditioned vehicle that would in fact allow illumination on terminal C in the "fan on" mode? Thanks in advance for any help given!
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geezrx 
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Location: Oklahoma, United States
Posted: May 10, 2014 at 9:22 PM / IP Logged  
OK...sorry,just realized that the last statement in my original post should have read "allow illumination on terminal E...not C.
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oldspark 
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Joined: November 03, 2008
Location: Australia
Posted: May 11, 2014 at 4:43 AM / IP Logged  
Being a rear demister switch it may handle the fan current, but you'll need a relay anyhow...
Use a typical 30A relay. Wire its NO contacts (30 & 87) across the Temp Switch. That can be done between the fan's GND wire and chassis or other electrical GND if that's easier (and cooler & cleaner etc).
The demister switch B to IGN +12V (eg, Fuse #13); D to relay 86, and E to GND as well as relay 85 to GND.
The advantage with that method is that it's an add-on (ie, no cut & break of the existing wiring) whose failure should not impact normal/standard fan operation, and there is no high current thru the demister switch.
geezrx 
Member - Posts: 19
Member spacespace
Joined: May 08, 2014
Location: Oklahoma, United States
Posted: May 11, 2014 at 8:02 AM / IP Logged  
Thanks for the reply oldspark. I'll purchase a relay and wire this up as you suggest.
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geezrx 
Member - Posts: 19
Member spacespace
Joined: May 08, 2014
Location: Oklahoma, United States
Posted: May 11, 2014 at 5:40 PM / IP Logged  
"Electrically challenged" strikes again! In the course of trying to buy a relay I am presented with the option to purchase a relay socket harness "with or without" a diode for the coil. It states this is beneficial if the relay will be controlled by an ECU. My vehicle has an ECU so...I read the description/use for diodes on here and get that it is a one way current "valve" but have no inkling whether I need one in this setup or not...anyone care to enlighten me?
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oldspark 
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Joined: November 03, 2008
Location: Australia
Posted: May 11, 2014 at 11:55 PM / IP Logged  
Sure. Tho your car has an ECU, it is not an ECU switching the relay.
And it's a (mechanical) switch doing the switching, hence not electronic as in ECU, computer, digital or analog circuit, etc.
However, tho there is no harm including such "spike suppression" diodes, many hereon claim to never have witnessed any damage by NOT including one - even when energised by ECUs etc.
I'd argue in your case it is optional but not necessary - ie, if it costs extra or adds inconvenience, forget it.
In some cases the spike might effect other circuits. I have seen LEDs or dash bulbs flicker in response to spikes on their supplies, and have read or heard of VERY RARE cases of damage - eg, a remote light or horn relay blowing an ECU or radio etc. However I'd argue those cases involve sub-quality ECUs & amps etc.   
The one thing I argue against is relays with inbuilt spike protection diodes. IMO it is much better to supply the diode externally. You can therefore add your own or replace a blown diode, and do not have to worry about which end of the coil is +ve or -ve. [Hence the convention with (old style?) Bosch/Hella etc relays where 86 is coil +ve and 85 is coil -ve (GND). To connect those the other way for a relay with inbuilt spike diode means a short from +12V to GND thru the diode and that's not the sort of smoking session most people look forward to.]
Modern relays avoid such polarity issues. They use resistors etc instead of diodes, else make the designer/user mount the diode as part of the relay's wiring base or harness.
A bit more (optional FYI) detail...
The diode is there to prevent voltage spikes that could damage other electrics - eg, electronics.
The spike occurs when the the coil is de-energised - ie, you switch off the relay - IOW open the coil circuit. The coil tries to continue its current flow and therefore generates a big voltage spike.
Such spikes are commonly up to 200V but almost always below 400V for 12V & 24V systems. Hence 1N4004 or 1N4007 diodes are typically specified for "spike quenching" of coils up to 500mA.
A "backwards connected" aka reverse-biased diode conducts when the spike exceeds ~0.7V, hence "clamping" any (say) 400V spike to between 0.7V below GND (ie, -0.7V since GND = 0V = zero Volts) and 0.7V above the relevant +ve supply - eg, the +12V supply (which is usually 12.7V on a full battery and typically up to around 14.5V when driving/charging).
All automotive 12V electrics should handle such a range.
In early electronic and digital car days, and more recently with cheap or pathetic designs, manufacturers may not have included suppression for spikes. However these days all +12V power inputs should handle (say) up to +16V steady-state, and spikes up to 400V etc.
Similarly any output that might be expected to drive a relay should have inbuilt spike protection - ie, a $0.05c reverse biased diode ACROSS its output(s).
Having said that, I still see the occasional "modern" product that specify that YOU must add the diode if driving a relay. (Like wth did they expect us to be using - a MOSFET or solid-state relay?)
Sorry if the above got a bit much. In retrospect it's all so easy... Once you realise a diode can only conduct (conventional current in the direction of its circuit symbol arrowhead (... and that the line on a real diode is the same end as the circuit symbol ie -->|-- ie so current can only flow out of the line end; the line (or brick wall) stops current flowing in from that end, you can begin to analyse and figure out your own use for diodes. (See the Diodes link at the top of this page.)
geezrx 
Member - Posts: 19
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Joined: May 08, 2014
Location: Oklahoma, United States
Posted: May 12, 2014 at 8:46 AM / IP Logged  
Thanks again oldspark. You answered my question and educated me at the same time...I like that!
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geezrx 
Member - Posts: 19
Member spacespace
Joined: May 08, 2014
Location: Oklahoma, United States
Posted: May 13, 2014 at 12:15 PM / IP Logged  
If I am understanding your instructions correctly, oldspark, my schematic of the circuit I will construct would be as shown below?
'86 honda civic si fan wiring -- posted image.
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oldspark 
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Posted: May 14, 2014 at 12:53 AM / IP Logged  
Yes, that is correct.
Congrats!
FYI - more learning (trivial)...
No need to "break" non-connected crossing wires.
The convention is that any "cross" is NOT joined; all joins are "T" junctions (see 3a in the pic below).
That may be best illustrated by Wikipedia's Circuit diagram's pic:
'86 honda civic si fan wiring -- posted image.
We used to use crossroads and bridges/overpasses to signify joints and non-joining wires. That got too tricky or messy to draw.
Then came dotted or not for joined & non-joined. But the dots got lost in reproductions - photocopies etc.
Hence now the lower practice - all joins are T's.   Note that old dotted/joined crossroads (1a & 1b) now have 45-degree deviations to produce the (angled) Tees (1c).
The latter is very tolerant to reproduction problems.
(Of course for OUR diagrams, we do as convenient! .. providing it's no ambiguous!)
Your "continuous" red wire is probably easier to draw, AND it conforms to the latest "standard". (Geez you're good! What is it with these people that reckon they're noobs or "struggle with schematic diagrams" - IMO they often seem to underestimate themselves. However caution is always advised, hence IMO never any harm asking for ideas, confirmation, etc.)
The "circuit operation" is easier to see if your upper & upper-right relay connections went downwards. It might then be more obvious that the upper 87 to vertically under 30 to GND is merely a parallel contact (switch) to the existing thermo switch. IE - if either are closed, then the fan operates (assuming the fan motor + has +12V to it).
That can be difficult else messy to do using "wiring schematics" - ie, circuit diagrams that use physical representations of components (switches, relays etc).
My diagrams are usually "circuit" diagrams where "pins" or terminals may be located anywhere in order to make analysis easier.
Maybe 12 to 24v automatic swap is a good example - ie compare Ween's "schematic" and my "circuit" in the 8th & 9th posts. Ween's is easier for wirers whereas (IMO) mine is easier to figure out how it works.
Note also that my circuit does not specify relay pins - I leave that up to the builder, hence they decide if they want to use Bosch type (30, 85, 85, 87 etc) or micro-DIN (1, 2, 3, 5 etc) or other relays.
geezrx 
Member - Posts: 19
Member spacespace
Joined: May 08, 2014
Location: Oklahoma, United States
Posted: May 14, 2014 at 10:23 AM / IP Logged  
I see what you mean. It is easier for me to "see" the circuit path in my revised drawing (all done in "Paint" which is so-so for this).
'86 honda civic si fan wiring -- posted image.
Again, the help is greatly appreciated!
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