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Here is a description from the older and newer Honda common manual of pump operation.
The "switch" is the contact points that have to open and close until pressure builds up.

There is a description of the relay circuit too. You can get both of those here=

 

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Discussion Starter · #42 · (Edited)
Hello back!

Please, dont want to bother the forum continuing posting updates about my Frankenstein... so, just tell me and I will stop now (or when I fix it somehow)

I could finally get a new pump, 3 psi just like the original VT700 1986, but without circuit, just 12v and ground cables coming out of it. Remember that VT700 86 has the original pump with an included relay circuit, and 3 wires going to it. Also I get some male/female connectors to make a clean connection (dont mind the wire colors, just the ones coming from the bike wire harness are the right colors) and an external fuel pump relay.

External fuel Shadow pump relay, mmmight not be the right one?:

And I tried to adapt the connections from a VT700 1985 fuel pump and separated fuel pump relay to my VT700 1986 like this:

Trying to follow the 85 diagram:

Adapting to 86 diagram:

It end like this:
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Result: the relay burnt :unsure:damn it! (its a solid relay, it started to leak something, so it burnt for sure), after I turn ignition key and RUN switch on, and give it start button at most 3 times I heard the sound of the relay melting (no fuses burnt anyway)

So, I for sure, I did something wrong or the relay adaptation is not possible.


Here, one question... the 3 wires coming from VT700 86 wire harness to the pump, blue signal, green ground, black 12+... must they have continuity between each other?
I test and the have continuity between each other (to my null knowledge this is wrong?), and also I get 12v+ from black and ground, and blue and ground (this one only when ignition key on and RUN switch on)

Any clue?

Thanks,
 

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Black to ground power is good.
You may show 12 volts on the blue with a meter, since it goes through the ignition coil winding waiting to be grounded by the ICU.
But with a load on it the voltage should drop low.
Put a small tail light bulb as a load and see if it drops.
If it is full power with a load there is a wiring problem somewhere sending full battery voltage on that blue wire.
 
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Discussion Starter · #44 · (Edited)
Black to ground power is good.
You may show 12 volts on the blue with a meter, since it goes through the ignition coil winding waiting to be grounded by the ICU.
But with a load on it the voltage should drop low.
Put a small tail light bulb as a load and see if it drops.
If it is full power with a load there is a wiring problem somewhere sending full battery voltage on that blue wire.
As always, thanks Swifty (will send you all some wine, promised 💪 after this karma ends, you all helped more than my called mechanic pals here :unsure:)

Here I connect a light bulb 12v ignition key on and RUN switch on.

Black wire and green ground wire to bulb I get strong light just as soon as turn the ignition key on (RUN switch on/off made no difference, as it is supposed I think)

Blue wire and green ground wire to bulb I get light, but little dimmer than with the previous connection (just a little) and not instantanly, seems it takes 1 or 2 secs to light on and slowly and stays on (little dimmer that with the black wire). When the last tests that blew the relay adaptation and maybe also the last pump circuit, it took about 10 secs until I heard electric burning with the blue wire. If I turn on/of the RUN switch, I mean the red one, it turns on/off the testing bulb.

Does this make any sense? I can try letting the bulb on connected to the blue wire and wait some more and see if it burns if it make any sense. Also I can test the amperage as you already teached me.

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PS: I will love to get a good mechanic/electrician here, I have no problem paying for knowledge and commitment but I really really really cant find any trusty one, and I went to many... they dont have the time, the patience, and knowledge... thats a hard one, its really frustrating but wont give up da#n it)
 

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This has me puzzled= "If I turn on/off the start switch, I mean the red one, it turns on/off the testing bulb".

If that is the start switch and the power to the ignition changes, that is no good.
The start switch should only send power to the start solenoid for cranking, not interrupt the ignition.
The only other circuit inside it is the headlight, and it IS turned off when you push the red button. So maybe here is a wrong wiring situation here.
Try your light test on the black/white wire to the coils and if it goes off and on there is a problem being connected to the wrong wires at the start switch.
 
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Discussion Starter · #46 · (Edited)
This has me puzzled= "If I turn on/off the start switch, I mean the red one, it turns on/off the testing bulb".

If that is the start switch and the power to the ignition changes, that is no good.
The start switch should only send power to the start solenoid for cranking, not interrupt the ignition.
The only other circuit inside it is the headlight, and it IS turned off when you push the red button. So maybe here is a wrong wiring situation here.
Try your light test on the black/white wire to the coils and if it goes off and on there is a problem being connected to the wrong wires at the start switch.
Very sorry about my terminology and english :-( what I ment with start switch... is the RUN switch (will edit the previous posts just to clarify if it helps in the future)

So, if the RUN switch is on (and ignition key on) there is 12+ on the blue wire. If it is off, there are no volts (that is supposed to be right I think)

Sorry, editing posts just now!

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Yes that is OK. It cuts power to the coils and ignition.
The blue wire is an extension of the ignition power. It comes from the coil winding back to the ICU waiting to be grounded to fire the spark.
 
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Discussion Starter · #48 ·
Yes that is OK. It cuts power to the coils and ignition.
The blue wire is an extension of the ignition power. It comes from the coil winding back to the ICU waiting to be grounded to fire the spark.
Thanks! so, seems cable stuff is OK, right? it must have been just the fuel cut relay from VLX600 or XFR750 (as the spects show) it is not completely compatible for some reason and thats why it burnt?

If it is so, I think the best thing would be leaving the "no relay built in" fuel pump directly to the black 12+v and green Ground wires... and thats all, no relay adaptation.
 

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You have been battling this too long .
I hate to say wire it directly because you lose the safety factor, but many old bikes have no safety fuel system.😕
 
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Discussion Starter · #51 ·
Yes, that kind of motocross safety device will work... but, damn I dont like it :geek:

Here found something more... after searching for cut wires or faulty stuff.

The relay Pietcard I bought (asking the factory) was specifically for Shadow VLX and XRV max voltage about 1000v and 4amps, and there is a difference in the "pulse signal kind".
This relay needs positive pulse signal to be activated, and VT700 86 (and possible others old bikes 85, 84...) needs negative pulse signal.

The realy factory told me that in this case... the relay shoudnt work but also shouldnt get burnt and that I might have another thing malfunctioning in the circuit. I also read that sometimes the CDI (the pulse unit) has some kind of problem where it wont give the negative pulse to activate the pump and the coils (not my case because coils seems to work fine, at least last time I started it up, for sure)

So, will install the pump directly to black +12v (leaving unconnnected the blue pulse signal wire) but will add a fuse of about 3 or 4 amps, as the 2 wires fuel pump (3 psi) I get asked about consumption and factory told it wont pass 1.8amps.

If I manage to get a "negative pulse fuel pump relay" will report back :p

Thanks for the support, as always.
 

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Another easy safety switch might be an angle sensor that if the bike falls over it stops the pump.
The newer bikes have them but I think it kills the engine first.
 
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