relays - someone set me straight on Mark VIII fan install - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 11 Old 10-31-2003, 06:26 PM Thread Starter
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Exclamation relays - someone set me straight on Mark VIII fan install

So I'm dicking with the relay to get power to the fan but I have a weird (in my opinion ) problem. I can't get any power to the side that sends power to the fan at all. I'm hooking up my relay as follows:

30 - Positive power from battery (through a fuse link)
87 - Positive power to fan's positive terminal
86 - Thermostatic switch
85 - 12V source from red MAF wire

I hooked up my volt meter to the 30 terminal to make sure I have power. I had ~12V thank gawd, and the 87 does not (at least it shouldn't, heh). However, when I ground the thermo switch and the relay closes, I lose all power at the relay's terminals...even the 30 terminal. So in other words, once I ground the the switch, there's no power at either the 30 or 87 terminals. Why would this happen??

If I haven't provided enough info, please let me know. I'd really like to understand what's going on. Thanks...


Jordan G.

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Ford Motorsport 351 balanced shortblock w/ KB flat tops, TFS TW heads (port/polish/milled for 10.5:1), TFS 351 U&L intake, 76mm C&L MAF, 70mm Accufab TB.
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post #2 of 11 Old 10-31-2003, 08:49 PM
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For a quick answer I would say that you have terminals 85 and 86 reversed. Keep in mind this is coming from an electrical moron. Worth a shot anyway.


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post #3 of 11 Old 10-31-2003, 08:59 PM Thread Starter
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Quote:
Originally posted by John91coupe
For a quick answer I would say that you have terminals 85 and 86 reversed. Keep in mind this is coming from an electrical moron. Worth a shot anyway.
Pfff, yeah, electrical moron with a gorgeous 9-second car . Seriously though, thanks for the response...

Well, I did a search and from what I gathered, 85 and 86 are interchangeable. I might try changing them around tomorrow for grins if I don't get any other leads. Thanks again...
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post #4 of 11 Old 10-31-2003, 09:23 PM
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What relay are you using? The 75A Bosch relays that I use do not have an interchangeable 85 and 86. 85 is negative and 86 is positive. Most other relays are interchangeable though. If you are not using the Bosch relay, I would try eliminating the thermoswitch out of the equation for test purposes. Just connect it to ground.

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post #5 of 11 Old 11-01-2003, 11:24 PM Thread Starter
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Quote:
Originally posted by Oktavius
What relay are you using? The 75A Bosch relays that I use do not have an interchangeable 85 and 86. 85 is negative and 86 is positive. Most other relays are interchangeable though. If you are not using the Bosch relay, I would try eliminating the thermoswitch out of the equation for test purposes. Just connect it to ground.
Thanks for the response Oktavius...

I am in fact using the Bosch 75amp relay also. I went ahead and tried switching the 85 and 86 posts with no luck. The relay closed, but I'm still losing power to the 30 and 87 posts?! Also, yeah, for simplicity's sake, I have been grounding the thermo switch on some bare metal.
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post #6 of 11 Old 11-02-2003, 08:35 PM
 
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I'm curious about the red MAF wire hook up. a relay would need two "grounds" right?
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post #7 of 11 Old 11-02-2003, 08:53 PM Thread Starter
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Quote:
Originally posted by FISHSTUNTS
I'm curious about the red MAF wire hook up. a relay would need two "grounds" right?
I don't think I do, but I might be wrong.

I think you need a 12V source and a ground to close the relay, and a power source coming in, and a power source going out to the thing you want to power. I'm basically just following this pic I have (I think I stole it off this site, heh):



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post #8 of 11 Old 11-03-2003, 12:43 AM
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I am stumped. I read through your post a couple of times and can't think of what is wrong. I dont understand how you couldn't read 12V power on the 30 terminal when the relay closes. It should read 12V no matter what position the relay is in, since you should be reading straight from the battery (well through a wire). I would check over your grounds again.

FISHSTUNTS is right about 2 grounds. There is terminal 85 on the switch side and there is terminal 87 on the power side which gets its ground after the fan. Just like the schematic above in the lower right corner.

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post #9 of 11 Old 11-03-2003, 12:59 AM Thread Starter
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Quote:
Originally posted by Oktavius
I am stumped. I read through your post a couple of times and can't think of what is wrong. I dont understand how you couldn't read 12V power on the 30 terminal when the relay closes. It should read 12V no matter what position the relay is in, since you should be reading straight from the battery (well through a wire). I would check over your grounds again.

FISHSTUNTS is right about 2 grounds. There is terminal 85 on the switch side and there is terminal 87 on the power side which gets its ground after the fan. Just like the schematic above in the lower right corner.
Heh, leave it to me to make the possible, impossible. Who'd have thought a freaking relay could be so difficult

I see what you and fish are talking about now. I mis-interpreted his post. Lemme get this straight...

30 - Positive power from battery (through a fuse link)
87 - Positive power to fan's positive terminal <----So you're saying this eventually goes from the + terminal of the fan to a ground, right?
86 - Thermostatic switch i.e. ground #2
85 - 12V source from red MAF wire

I guess I'm going to tinker with it tomorrow to see what I screwed up. If I can't get it right, I guess I'll call my mechanic and give him a good laugh
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post #10 of 11 Old 11-03-2003, 01:13 AM
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That is the idea, but you still have 85 and 86 switched around. I know that mine would not work with them reversed. The diagram is right on the side of the relay.


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post #11 of 11 Old 11-03-2003, 01:29 AM Thread Starter
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Quote:
Originally posted by Oktavius
That is the idea, but you still have 85 and 86 switched around. I know that mine would not work with them reversed. The diagram is right on the side of the relay.
Well, even though this relay is still goofy, thanks a million for your input/help

I'm gonna switch the 85/86 tomorrow one mroe time and see what happens. Thanks Oktavius...
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