P700m4 Auxiliary switches and lights

[Jayrock]

Hello Guys I recently completed adding two aux switches to run lights and power to the rear for a sprayer. Then I added another 12 volt connect to charge phones, cameras etc. I also added a light to tell me when the fan is running. This is where I ran into trouble, I found the fan wires one blue and one green, both are hot when the fan is running and the green drops out when the fan goes off. Can you tell me where to connect the hot lead from my light? Thanks Jay...

 

[Hondasxs]

U sure they are both hots?
Hang on. I'll check.

 

[Hondasxs]

Blue is 100% confirmed Hot coming from the fuse box.
Green is your choice. Should be a ground. It comes from the ECU box.
The way I thing it works is...
When the sensor in the case gets to (x) temp it grounds out. Then the fan comes on.
Remember most things on our units work off a negative switch, not positive.
therefor, it is the ground you need to be connecting here.

If someone can confirm.
I am still looking it up.

 

[Hondasxs]

Ya. thats right. The green is ground.

If you wish to confirm. Hook a test light to the battery hot. Then to the green when the fan comes on. Should have light!

 

[Tramguage1]

Not sure on Honda but have quit a bit of experience with automotive ecm's. You are correct that the ecm latch's the ground side.

 

[Jayrock]

Ya. thats right. The green is ground.

If you wish to confirm. Hook a test light to the battery hot. Then to the green when the fan comes on. Should have light!

I did try this and confirmed both blue and green would light the test light, when the fan shuts off the test light will go off when connected to the green. This would work this way, but my light would be on all the time except when the fan is running.

 

[Hondasxs]

@Jayrock.
I do believe your test light came on. I'm just not sure how to explain it.
Have you ever tested for a parasitic battery drain using a test light?
I think this is the effect you are seeing in your test light.

maybe someone who knows about this can chime in..


Anyways.
Here is the info from the service manual dealing with the fan wires.

 

[ohanacreek]

@Jayrock.
I do believe your test light came on. I'm just not sure how to explain it.
Have you ever tested for a parasitic battery drain using a test light?
I think this is the effect you are seeing in your test light.

maybe someone who knows about this can chime in..


Anyways.
Here is the info from the service manual dealing with the fan wires.
View attachment 5860

A switched negative circuit always has power so if you're trying to track down the wiring a test light will sometimes close the circuit when finding ground. You gotta think backwards. Depending on where in the circuit you're tapping to test you might be getting power on a "ground wire" you might be completing the circuit. Depends on which side of the relay that switches the circuit with the ignition you are on its still the ground side of the circuit. (According to color code and login, because the main switch or relay is where the color code changes but there is a secondary relay controlled by the ignition that gives in the case of a switched group system , ground. Instead of how we colonists wire everything where the positive feed is switched with the ignition. )

It was a PITA trying to figure out how the wiring in the Honda wiper motor was setup until @spifyd pointed out its a switch negative system. I blew several fuses in my bench setup trying to figure that one out.

 

[Hondasxs]

^^ what he said.... whatever he said? Lol.

 

[Hondasxs]

@ohanacreek, So. What we got to do to get a led light to come on when the fan comes on?

 

[Hondasxs]

I bet if u test the 2 fan wires together you will get light. If so. Blue is ur positive and green your negative = LIGHT

Ya.. that's it. Where thinking about it too hard. It should be able to hold a small led.

 

[ohanacreek]

Sounds like that might be right, not sure, might need an additional diode in the circuit (they act like check valves), you'd need to look at the diagram.

 

[Tramguage1]

I'm pretty sure that the fan has a relay that is energized by the ECM normally you don't run high current items through an ECM. So you need to find that relay and put your light on one side of the relay.
Hondasxs is there a wireing diagram for this model? If so , post it up and I will figure out where the best place is for a lite to be installed.
I installed a manual bypass rocker switch with a lite on my rock krawler and used the lite to come on anytime the fan was running.the ecm would normally control the fan buy engine temp.

 

[Jayrock]

I'm pretty sure that the fan has a relay that is energized by the ECM normally you don't run high current items through an ECM. So you need to find that relay and put your light on one side of the relay.
Hondasxs is there a wireing diagram for this model? If so , post it up and I will figure out where the best place is for a lite to be installed.
I installed a manual bypass rocker switch with a lite on my rock krawler and used the lite to come on anytime the fan was running.the ecm would normally control the fan buy engine temp.

You guys are the BEST!! I wired in my light ( backwards in my mind) the way you said to do it and it works awesome. Thanks again for your help. This is an awesome place for help, support & knowledge......

 

[Hondasxs]

@Jayrock, what did u end up doing to get it to come on with the fan?

 

[Jayrock]

@Jayrock, what did u end up doing to get it to come on with the fan?

I connected the hot lead from my light to the green fan wire and connected the negative from the light to 12 V positive and it works great.. Thx again for your help on this.

 

[JACKAL]

I connected the hot lead from my light to the green fan wire and connected the negative from the light to 12 V positive and it works great.. Thx again for your help on this.

I would have been in the same boat, would never have thought to run ground wire through the switch. Thanks everyone for clearing this up.