Help with identifying something on fuse box

[8lugnutz]

I have a 1980 K10, built 12/79, and the fuse box has an addition to it that I haven't seen before. On the right just above the flasher is an additional block that is empty, and I can't figure out its purpose. There are three wires that are coming into it, a pink/black fed from the main fuse block, a dark green, and a black. Here is the pic:



The black and green wires disappear into the harness and I have no clue where they go. I searched the wiring diagrams that forum member Hatzie has posted, and I can't find any reference to this additional panel. Any thoughts?
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[Jonboy]

Pretty sure pink is switched power, and the black will be a ground. I would be a little concerned about the wire pulling power from the flasher. Looks a little sketchy to me. I think I have a '79 wiring diagram somewhere, but need to look for it. They are pretty readily available on ebay for around $10. I used mine quite a bit on my'79.

[8lugnutz]

The orange one isn't pulling from the flasher. It's a non switched for the radio that came unplugged, it's now in the right spot. My presets on the radio kept disappearing, that's what got me started on this rabbit trail..
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[8lugnutz]

Does anyone know what the additional plug on the top right above the flasher is for? Maybe a seat belt buzzer or something? I know my truck isn't that unique.

[motornut]

Originally Posted by 8lugnutz

Does anyone know what the additional plug on the top right above the flasher is for? Maybe a seat belt buzzer or something? I know my truck isn't that unique.

i think the buzzer is higher up(can see one)
but some were combined with headlights too
pink and black strip seems to power the cluster/running
could it be low power relay ,turns on a bigger relay/flasher for something,

[willett]

Sorta looks like a spot for a horn relay
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[8lugnutz]

Motornut - that was my thought too, maybe a relay

Willet - horn works, so I don't think that's it. I'll try to trace the two wires and see if I can figure out where they are going.

Thanks for the replies, but it's still a mystery!
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[8lugnutz]

So.... If you have been following my build thread, you would know that I am working on my dual fuel tanks..... Turns out, this is the mysterious green wire I was looking for that goes to the switch, which would explain why I had no voltage at the tank. Who knew that these two would be related!?!?

On the back of this little doo-dad is four wires:

Pink/black = Switched power
Orange = Constant power
Black = Ground
Green = +12v to fuel tank switch

Now what I can't figure out is what goes in that slot. Its kind of odd shaped, take a look:



Far as I can tell, it has to be either a relay or a circuit breaker. Any ideas?

[superwade57]

I've got a dual tank 80....in storage.... ill have to try to remeber to look this weekend.
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[8lugnutz]

Thanks, Superwade, I also pinged TexasJeff who has an '80 model too. He helped me out with a picture of his switch bezel on another thread.

[hatzie]

If the diagrams will help. Full foldout page PDFs of the 1979 & 1980 10-30 GM light truck diagrams are in my signature.

[8lugnutz]

Hatzie, those were the exact diagrams I was referring to in the original post, and linked to on my build page. I didn't see any reference to a sub panel on the fuse box, and there is no mention of a relay or circuit breaker.

Your diagram thread was the first one I subscribed to!

[8lugnutz]

Ok, so I got this all figured out. The space in the fuse panel is for a relay, part number 14014527. According to the guy I talked to at the dealership, it is specific to the 1980 year model, so I guess our 80 model trucks are that unique after all. Be warned that this is a discontinued part!

Here was his explanation. In earlier model trucks if you ran out if fuel on the primary tank (default tank) and switched over to the secondary, as soon as the ignition switch was engaged, it cut the power to the solenoid, which in effect would default back to the empty tank. The solution to the problem was the relay, which explains why there is both a constant power (orange) and a switched power (pink/black). When the pink/black is cut off by use of the ignition switch, the relay switches to the constant power to keep the solenoid engaged into the secondary tank, provided that the switch is in the LH position.

Here is a picture of the relay:

[hatzie]

Originally Posted by 8lugnutz

Ok, so I got this all figured out. The space in the fuse panel is for a relay, part number 14014527. According to the guy I talked to at the dealership, it is specific to the 1980 year model, so I guess our 80 model trucks are that unique after all. Be warned that this is a discontinued part!

Here was his explanation. In earlier model trucks if you ran out if fuel on the primary tank (default tank) and switched over to the secondary, as soon as the ignition switch was engaged, it cut the power to the solenoid, which in effect would default back to the empty tank. The solution to the problem was the relay, which explains why there is both a constant power (orange) and a switched power (pink/black). When the pink/black is cut off by use of the ignition switch, the relay switches to the constant power to keep the solenoid engaged into the secondary tank, provided that the switch is in the LH position.

Here is a picture of the relay:

So this keeps the valve energized in the START position... not with the ignition off...?

[legendman]

I have a harness out of a 82 K30 with dual tanks, I remember those color wires - pink,green and black running to the dual tank stuff.
I will check when I get home later

TREED OPs post above lol

[kalbert]

That doesn't make any sense at all? The relay turns on when the key is turned off to keep the tank selector valve energized? Seems like that would be hard in the battery? Isn't the tank selector switch a momentary contact that energizes the solenoid briefly to make the valve change while you're pushing the switch? The valve is not sprung it isn't normally closed or opened, it is flipped whatever way the current last ran through the coil isn't it? Not calling the guy a liar or an idiot, it just doesn't seem right and I'm wondering if there is more to the explanation.

[8lugnutz]

Originally Posted by kalbert

That doesn't make any sense at all? The relay turns on when the key is turned off to keep the tank selector valve energized? Seems like that would be hard in the battery? Isn't the tank selector switch a momentary contact that energizes the solenoid briefly to make the valve change while you're pushing the switch? The valve is not sprung it isn't normally closed or opened, it is flipped whatever way the current last ran through the coil isn't it? Not calling the guy a liar or an idiot, it just doesn't seem right and I'm wondering if there is more to the explanation.

Kalbert, forgot to address your questions. As it was explained to me, yes,
the relay turns on when the key is in the start position or is turned off to keep power supplied to the solenoid, but only when the switch is in the LH position. The RH position doesn't provide power. I will be digging into this further and searching out the facts when my relay comes in, and will post my findings here.

Regarding the switch type, as I understand it the older models came with an ON - ON switch. In the newer trucks, the switch is momentary. My '87 CC had a momentary switch, with the bezel that said "Depress Fully", if I remember right.

[8lugnutz]

Makes sense if you think about it. If the default tank is empty (RH), and you need gas supplied from the LH tank, when the ignition switch cuts power to the solenoid, it moves back to the empty tank. With the relay in the picture, when the switched power is cut, it engages the always on voltage supply to keep the solenoid engaged, and therefore drawing from the LH tank. The solenoid requires voltage to move to the LH tank position. The system was designed to always move to the default (RH) tank in the event of an electrical failure. At least that is how it was explained to me.

[Sabaka454]

[8lugnutz]

Switched power is provided when the ignition key switch is in the "run" position, but not the "start" position. When your ignition switch is in the "start" position, meaning that you are physically turning the switch all the way to engage the starter, there are electrical circuits that stop providing power. Your radio circuit is one of these, it gets turned off when you start the vehicle. Power is cut on the fuel solenoid circuit in the exact same way, or it was prior to adding the relay. It makes sense to me. Not sure if this is only '80 model or not.

[kalbert]

Ok, I think it makes a little more sense now, the turning on while cranking part anyway. I'm still skeptical that it would be on all the time though, I'd expect that to drain the battery overnight if not sooner?

[superwade57]

This all may explain why you have to push and hold tank selector in the later trucks instead of just push the toggle either way?

[superwade57]

heres whats in mine,,,

[8lugnutz]

Superwade, That confirms the part number, thanks for the snapshot!

Hatzie, that is my suspicion, but I won't know until my relay comes in and I do some testing. I will definitely reply to this thread with what I find out.

[8lugnutz]

The relay came in yesterday, and I did some testing this morning. Below is the wiring diagram of my truck, and the results of the testing that I peformed. To answer the previous questions regarding the operation of this relay: once this relay is plugged in, and the keyswitch is moved to the RUN position for the first time, that relay is engaged, until power is removed from fusebox by disconnecting either the battery cable or the constant power (orange) wire. The position of the selector switch either sends power to the solenoid (LH position) or not (RH position). See the diagram below, and let me know if there are any questions, I will try to answer them.