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fan motor switch honda vt750

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Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: January 14, 2015 at 2:58 AM / IP Logged  
IMO yes to your verbal, but no the diagram.
Keep the "fan motor switch" to GND 85 of the FAN relay - ie, 86 to IGN, and 30 & 87 in series with the fan - ie, between its + and +12V (battery; fused) for a grounded FAN.
It looks like your fan is "single wire" - ie, its GND is thru case to bike chassis/engine GND - but if the Fan motor "-ve" has a wire INDEPENDENT of (case) GND, it could go thru FAN Relay contacts 30 & 87 to GND.
The latter is how usually done on vehicles since "GND switching" requires less wire (no wire to +12V, instead a wire to a nearby chassis GND) and that parallel relays or switches for alternate fan-on commands/sensors are simply paralleled whereas the +12V switch's equivalent requires diodes to prevent power backfeed to other +12V sources IF they are different (eg, battery, IGN, ACC, ECU +12V, etc). Also no lengthy +12V cable to short to chassis.
The FAN MOTOR SWITCH (sensor with switching to handle fan current) has a lower setting than the "TEMP LIGHT" switch which (probably) is a mere warning of impeding engine damage or that their may be a FAN or coolant problem etc.
If the "TEMP LIGHT" merely indicated "I'm hot and the fan is on", it would switched by the FAN circuit.
A relay (86) from the TEMP LIGHT with 30 & 87 connected in parallel to FAN RELAY's 30 & 87 will switch on the FAN in case of FAN MOTOR SWITCH or FAN RELAY failure. (If it's a relay fault you interchange the 86 & 85 between the relays (ie, FAN MOTOR SWITCH relay and TEMP LIGHT relay) to resume normal operation.
Using the temp warning to turn on the fan is a great backup, but it's not good long term for the engine, but it's still way better than the engine blowing if you the light wasn't working, or if you ignore etc... [KIDDIES - please learn to check initial IGN-on warning light tests, and do NOT ignore them if they light later...   {I recall the driver that ignored the little red "O" light. The next 2 minutes cost them >$1000... the engine seized. d'Oh!}]
Adding an extra temp sensor - maybe a $5 Klixon temperature switch - means sensor redundancy.
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