Popping fuses on Air on Board switch power wire

So I have a weird issue I can’t seem to isolate and am looking for ideas.
I made an aux fuse panel, powering a set of lights and an Aux power supply to my dump trailer.
Pic shows how it’s set up more or less.
I have a Continous duty solenoid that’s delivering power through 4ga wire to the rear of my truck to help charge my dump trailer. This solenoid is activated via a switch (Air on Board switch). The trigger wire is activating a relay, which in turn activates the solenoid. Both the power supply to the relay and the trigger wire are fused.
Inside the cab, the ignition controlled power supply to the switches is fused as well, stealing power with one of those add a circuit gadgets.
I am popping the add a circuit fuse to the switches. It had been a 7.5a fuse. It’s powering 3 switches. I’ve since put a 15a fuse in as that’s all I had and I needed a switch on (2Lo switch) to finish where I was going.
I’m trying to figure out why I keep blowing that fuse.
As a side note, I previously ran the switch directly to the solenoid. It worked fine for about a year. The the switch was burned out. Then the second switch burned out. So I added the relay in between now am blowing the ignition controlled fuse.
The trailer will draw 40amps. (Resettable 40a CB on trailer end that cycles off and on while dumping with high current draw)
Could the solenoid be somehow backfeeding weird causing the switch or that fuse to blow? Even shutting the switch off before the high power draw does not save the fuse.
I’ve searched for a chaffed wire to no avail. Replacing the solenoid is next but I hate throwing parts at it for no reason.....
Thanks for any insight.

 

If the switch is isolated from the solenoid by a relay, then there should not be a way for the solenoid to back feed. I am guessing that you have something hooked up incorrectly at the switch or a cut wire grounding out. The draw to trigger the relay should be minimal, have you used an amp meter to see where the juice is going? I think that would be the next step to figure out what is going on.

 

So switch to relay and relay to solenoid? Specs on the switch, relay, and solenoid? When does the fuse blow? Is it when switched on, off, immediate, random, etc.?

I know you said the switch fuse is the one blowing, but just to check, you know the add-a-fuse gadget needs to be in the correct orientation, right? If it's backwards it runs both circuits through the location for the original fuse.

 

Open fuse has one cause current draw to high for the fuse. Something shorted loose connection

Though in this day who knows fuses open lower or higher then the rating

 

As it worked for about a year without the relay (direct to solenoid) then has worked for a while with the relay, it would seem it must be a short somewhere but danged if I can find it

The switches are only rated to switch 3 amps I believe. Relay is a 40a, solenoid is 250a continuous. The fuse blows when I’m running the power through the solenoid, but usually it’s been switched on for 2-3 minutes before it pops the switch’s power fuse. I have not had an ammeter on the circuit to check that and with the intermittent popping I’d doubt I’d see anything abnormal but it’s worth a try! I must have a short to ground that I can’t see, last place to check is to pull the wiring out of the firewall. Hopefully this weekend in the shop.....
Thanks for the suggestions!

 

Try a new fuse direct off the battery too, to eliminate anything with the stock wiring.

 

Can you draw up a schematic based on what is wired in the truck? It sort of sounds like something isn't quite wired the way you think it is.

 

What "0xDEADBEEF" said.

Without a wiring diagram it will be like shooting a shotgun shell with birdshot at a humming bird; not much chance of hitting the target when all the projectiles and target are are so small.

And we need to know how many amps are on the circuit.

Without knowing how things are wired, and the amperage of each item on the circuit we will be guessing and that will not provide a good result.

Regards,

Jim

 

Thanks for the suggestions so far. Got the truck in the shop today so can better look at things. I spent more time trying to find a way to draw something neat and more understandable than hand drawing, than it would have to have hand drawn the schematic. As it worked fine for a year, I’d think it’s all ok. And the new issue is intermittent so I’m guessing I have a pinched wire someplace. I have wires routed around underneath the dash and they come in near the clutch pedal, last night at quick glance I saw the clutch pedal spring has been moving my rats nest if a wire bundle around so a better tidying job if that is in order. It’s likely chaffed somewhere up there and I just haven’t looked good enough so that’s step one today. I believe my multi meter will show me Amp draw (years ago I may have blown the multi meter fuse for ammeter and couldn’t find a replacement weird size fuse) but I’ll give it a go today as well. I Just can’t see the relays taking very much current to close....
Flurries are in the air so it’ll be a good day to have the fire going inside and tinker....

 

So.... put multi meter on the add-a-fuse line and had less than 1 amp draw with 2/5 switches powered. Also hooked up dump trailer and checked it with the solenoid powered and all was the same as it should be.
I found my solenoid trigger wire chaffed in 3 spots from the poor routing and the clutch spring catching it. This caused the failed switches.
I could not find a reason for the ‘add-a- fuse’ fuse to be blowing. Well, there was one crimped connection (On the +12v add-a-fuse line) that I had to make (rather than soldered) and it was loose-ish but not falling out, maybe that poor connection caused it.
All wiring cleaned up, loomed and tied up the way it should have been. I had done the install in the cold outside and never ‘finished’ it apparently!
I’ll have some more switches on order So I can hook the rest of my stuff back up and retest the load.

I currently have(had) : 2Lo mod, rear anytime camera, 2 switches for future lighting, and The Aux power through the solenoid for the dump trailer charging. All switches trigger a rely (minus the camera). The one light switch activates the relay when high beams are on. (This one worked fine while I had lights installed)

Hopefully problem solved. I have nothing bad to say about the Air on Board switches, obviously this was my fault! Hoping I can get new switches without too much delay!