12 volt key on source

[tphsmith]

please help me out here, I'm asking for guidence to where keyed source power is at on the trucks, mine is a 72. and in the cab or on the fire wall where are these 12 volt key sources at. I have schematics but it helps if you can read them, well they confuse me because I dont know how to read them.

I am trying to connect my fuel pump, (electric) and where I have it now it runs when they ign. key is in start and run, but when I shut the key off the engine still runs untill I unplug the wire for the fuel pump, this is making me pull my hair out please help

[sneakysnake]

You can hook it to the "Ign unfused"and put an inline fuse or you might consider running your pump through a relay.

[tphsmith]

welll, the pump is running threw a relay now the power to the relay is coming ign. key power source? now I just dont get it, can I maybe connect to a wire off the ignition switch?, or back to original question, where are there places I can connect this wire for I will have Ign. key on besides what shows in pic above because this is where its at now. (wire in pic)

[Elephanthead]

sweet, that is switched, now I know where to hook up my electric choke.

[mrein3]

One thing to consider and I'll relay it in an example.

I converted my non-A/C truck to A/C. I used all used parts for the conversion. This meant that I had to replace the switch in the controller, the melted switch connector, and while I was making everything good I rebuilt all the wires in the harness I bought. While doing this I decided to run the hi-speed fan off a relay with power coming from the battery. The factory relay that came with my used stuff didn't work so I purchased a relay identical to the realys I installed in other places on the truck so I only had to carry one spare for the whole truck.

I got done, everything worked, and life was good. Until a few months later. I pulled into the shed and turned the key off but the truck kept running. After similar hair pulling exercises I figured out what was happening. When the blower motor was in the high-speed position, the relay I installed was "hot". This relay was feeding +12 into another wire that was connected to the ignition wire I installed when I switched to HEI. This kept that circuit alive until I flipped the fan off high-speed.

The problem with these old trucks is that there are only so many +12 ignition and +12 always hot wires available. When you wire up a bunch of crap you can get wierd feedback loops.

Now on your truck, think about all the extra crap you've installed. Did you install another relay someplace that could be feeding back to the 12 volts you're sending to your pump relay?

FWIW, my fix was to make sure the fan wasn't on high when I shut the engine off or flip it off of high when this happens. Some day when I'm independantly wealthy I'll purchase one of the aftermarket fuse panels to run all the crap I have with more discrete circuitry.

[sneakysnake]

I got into this when I hooked an electric fan on my radiator without a relay. If your relay is wired right it cant backfeed because the points open the curcuit to the device when its turned off, Here is a simple diagram to look over to understand the workings of a relay.

[tphsmith]

sorry but I cant figure this out, today I tried a few other keyed on places to connect this issue to, but no results.
it has been a few months since this (I wired it up) but now this is a big hang up for me. maybe its because Im using a relay for the electric fuel pump and also connected is a Roll Over Crash shut off switch, this has a relay also, and the relays maybe are an over kill and they are causing the issue of when I turn the Key to shut off the engine, the engine stays running.
please everyone I need help on this.

[heavy71chevy]

why not wire it into the key switch so it only has power when the keys on...id just stick a volt meter on the wires till I found one that was only hot when the keys on and use a water tight splice to wire it in...eliminatate the problem and you could still run the crash cut off

[mrein3]

Originally Posted by heavy71chevy

why not wire it into the key switch so it only has power when the keys on...id just stick a volt meter on the wires till I found one that was only hot when the keys on and use a water tight splice to wire it in...eliminatate the problem and you could still run the crash cut off

Yes. Use a volt meter or test light and find a 12v source that is only hot when the key is on. Make sure you have everything else powered up to help determine if you are getting a feedback loop somewhere. Either one of those two "IGN UNFUSED" terminals should work. Just make sure you put an in-line fuse in the wire you run to the pump.

Also make sure the 12v wire you run from "IGN UNFUSED" is connected to "86" on the pump relay and "86" on the "Roll Over Crash shut off switch". "30" on both of those relays needs a FUSED 12v wire from the battery (always hot). "87" on the fuel pump relay should go to the red wire on the pump. "87" on the Roll Over Crash shut off switch relay should go to the red wire on the roll over crash shut off switch.

Wait a second. What is the roll over crash shut off switch? Is that built in to the pump? Or is it some other sensor?

You should post some pictures of what you have going on.

[sneakysnake]

Is your rollover switch killing your fuel or your Ignition(both)?You cant have any electric motors tied directly to the ign source (or through a relay that can get back to the ign when in open pos) or they will feed the dist coil,even with the key off the wiring is still linked, the key only stops the battery source from the fuse box but they essentially linked together. a relay not only helps to carry a large load it also isolates a device from the rest of the wiring when its turned off.

[tphsmith]

the crash roll over switch is seperate , diffrent item from the fuel pump. when I unplug the wire (i did the wiring so let me tell ya up front, this is probably self inflicted problem with my wiring) that is connected to supply voltage to the fuel pump, I have the crash roll over switch tied into this also. so when I unplug this wire it shuts everything off, engine and fuel pump. but this is not right, we all know I want the Ign. key to kill everything. So what I think I need to do is un wire the Crash switch, (I wish the guy at the Hot Rod Shop would not have talked me into buying this dang switch now, LOL) and just have the electric pump hooked up and see if this corrects the normal funtion of Ign. key off to shut the engine off. But guys I realy am asking for your help here, I am going to go look at the wiring now and hopefully get just the Fuel pump wires connected to see if the Ign key will work at that point. I'm wondering since there is 2 relays in this cluster, one for the fuel pump and one for the crash switch if they are working agianst them selves, plus the relay on the crash switch, the numbers are not 30, 85,86, ect they are 1,2,3,4 this is killing me thanks for your guys help realy

[sneakysnake]

Are you sure the fuel pump is source of feed back voltage? No blower or radiator cooling fans running?The fuel pump really should'nt run long after the power is off to cause this problem.You may have a relay feeding a relay, so that the key no longer kills the power to it after its energized. but its hard to diagnose from here.

[tphsmith]

sneakysnake, the relay double feed is what I am thinking also, I need to go back a trace this down, I will keep you dated to what I find

[69C10@16]

Here is how you would wire just your fuel pump. I dont know how your crash switch works so I cant help you there.

[tphsmith]

haa, got it, it was a double feed in the two relays, how I didnt burn wires? anyways it all works good and the sound of this LT1 running just makes me P my pants

[texanidiot25]

Originally Posted by 69C10@16

Here is how you would wire just your fuel pump. I dont know how your crash switch works so I cant help you there.

Is this diagram universal for all relays? Need to wire a relay for a different project, but don't remember what numbers are on the relay, and lost it's diagram..

[tphsmith]

yes that drawing is pretty much for all relays