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Hayabusa Killer
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Discussion Starter #1
I am going to be wiring up my fuel system tomorrow and need to know which wire to use as my trigger on the relay. This is my setup I will be using.

2 stock pumps
single 75 amp Bosch relay
I am going to use the + and - that go into the hanger as +'s and I will ground out the pumps on the hanger then ground the top of the hanger to the body of the car.


The relay has 4 connections and this is how I will run them

pin 85 will be 12v trigger ( I need to know what wire to use from the fuel pump ECU)
pin 86 grounded to body
pin 30 battery input wire the battery is located in the truck so it will go straight to it
pin 87 will go out to the + terminals on each pump


What wire should I use to trigger the relay? I want it to have 12 volts all the time but I also want to keep the safety feature that the fuel pump ecu gives you (if the key is on acc it does not run the fuel pump without the car running) My car is a 1997 so using this information which should I use, solid blue wire, or the blue/red wire?

http://mkiv.com/techarticles/12v_mod/12v_mod.htm

Thanks

Cisco
 

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well i dont own a mk4 supra but i would think that if you used a test light, and found the wire that was hot for a few seconds when you turned the key on and then turned off, you've found the wire..
 

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Hayabusa Killer
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Discussion Starter #3
I might do that tomorrow. I am just unsure if one of the wires only has 9 volts going to it and if thats enough to power the relay.
 

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I might do that tomorrow. I am just unsure if one of the wires only has 9 volts going to it and if thats enough to power the relay.
well in that case hit autozone, get a cheap lil volt-a-meter and test and make sure ur getting 12v... good luck.. how much power are you trying to make BTW
 

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Hi

well i dont own a mk4 supra but i would think that if you used a test light, and found the wire that was hot for a few seconds when you turned the key on and then turned off, you've found the wire..
I used that wire first, but had to change cus the pumps stopped... Now it`s on a constant ignition on wire...
 

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95 Supra under the knife.
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358 Posts
Im actually doing this right now. But Im also wondering which wire to splice into? Or does it not matter??? thanks Jim
 

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ex BPU'er
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I just did this. The trigger I used was the 12V source of the fuel pump ecu. Not sure if that is 100% right, but I think it works (my car is still in construction)
 

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Hayabusa Killer
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722 Posts
Discussion Starter #10
Thanks.

I also got another problem. I over tightened the prong that the positive wire on the fuel pump connects to and broke it off. There is about 3-4 threads still there. How do I go about fixing this? I was thinking about getting a piece welded on. Here is a pic of a MKIV fuel pump so you can see what I am talking about.

http://www.mkiv.com/techarticles/fuel_pumps_test_2/denso340pump-1.jpg
 

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95 Supra under the knife.
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358 Posts
I have another question about the"trigger" wire. I know alot of people on this forum do the 12v mod to there cars, you know splice 2 wires together to make the pump run at 12v all the time. I was wondering if it would be ok to do the 12v mod (splice the 2 wires together) and then use that as the trigger. Or can you only splice into one wire???
 

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You do NOT want to do the 12v mod. You want to have the fuel pump ecu trigger your relay just like the gigantic photo posted above. This way your pumps will only operate when they are supposed to. There is no splicing involved.
 

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I have another question about the"trigger" wire. I know alot of people on this forum do the 12v mod to there cars, you know splice 2 wires together to make the pump run at 12v all the time. I was wondering if it would be ok to do the 12v mod (splice the 2 wires together) and then use that as the trigger. Or can you only splice into one wire???
Doing the 12volt mod bypasses the fuelpump ECU... so there would be no trigger since it is the fuelpump ecu that generates the trigger voltage. Doing what you are saying would be the equivalent of just doing the 12volt mod with no relay.
 

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95 Supra under the knife.
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358 Posts
Doing the 12volt mod bypasses the fuelpump ECU... so there would be no trigger since it is the fuelpump ecu that generates the trigger voltage. Doing what you are saying would be the equivalent of just doing the 12volt mod with no relay.
Gottcha after I thought about it more I realize it was a stupid question. ha I forgot to mention that my car is an N/A converted to TT, So my wires are different colors than the wires used in a TT. Does anyone know what color wire I use as the trigger??? thanks Jim
 

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Hayabusa Killer
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722 Posts
Discussion Starter #16
I wired it with the blue with red strip wire. This wire is 9 volts then becomes 12 volts when the fuel pump ECU lets it. The other wire is a constant 12 volts. It operates the relay even at 9 volts. The only problem I found was when I first start the car I can hear the relay click about 3 times. I am wondering if I might be better off wiring it with the constant 12 volt wire.
 

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I wired it with the blue with red strip wire. This wire is 9 volts then becomes 12 volts when the fuel pump ECU lets it. The other wire is a constant 12 volts. It operates the relay even at 9 volts. The only problem I found was when I first start the car I can hear the relay click about 3 times. I am wondering if I might be better off wiring it with the constant 12 volt wire.
Correct. However be aware the that wiring changed colors on the OBD2 Supras. But the way you have it is the right way. My relays work just fine with the 9v signal. I would not wire it with the constant 12v.
 

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6 speed
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if i have 2 densos, can i tap 2 wires from the blue/red striped wire to trigger both relays? i want them running all the time and the third denso will be triggered by my AEM. also wouldn't it make more sense to wire the relays to a 12v mod converted wire for the relays? i thought the relays required 12v for the trigger.
 

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if i have 2 densos, can i tap 2 wires from the blue/red striped wire to trigger both relays? i want them running all the time and the third denso will be triggered by my AEM. also wouldn't it make more sense to wire the relays to a 12v mod converted wire for the relays? i thought the relays required 12v for the trigger.
Read the entire thread. The picture in post #6 shows you how to hook up two pumps. Wire it exactly like the picture. The relays will still trigger off of 9v (yes you can tap two wires off of it). The 12v mod is not something you want to do. It will make the pumps run anytime the key is in the ignition even if the motor isn't on. Just follow the picture above and have your AEM turn the 3rd pump on.
 

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Hayabusa Killer
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722 Posts
Discussion Starter #20
Correct. However be aware the that wiring changed colors on the OBD2 Supras. But the way you have it is the right way. My relays work just fine with the 9v signal. I would not wire it with the constant 12v.

Yup my constant 12 volt is solid blue (1997) and others are blue/orange (1993-1996) or black/red on (1998).

Does your relay also click when you first start the car? I am thinking its caused becasue when you are starting the car its not running for the first second and the relay is turning off and on really fast.

Now about the fuse. I am using a single 75 amp relay what size fuse would you put between the relay and battery? I was thinking a 50 amp.
 
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