Need help with my "run" and "crank" relay power source.

[jatepper]

So, I have some accessories powered by an under dash relay. I ran a 8 AWG wire from the battery to the relay for it's main power source and I'm trying to get my switched power from a power source that is hot it both "run" and "crank".

From what I understand, relays use very little power to turn them on. I found the wire (shown in the photo link) from my ignition system that is hot it both run and crank, and I'm using it to turn on the relay. The problem I have is that it keeps blowing the 14A fuse pictured below.

My question is why on earth is it blowing the fuse? It should be drawing next to nothing. My second question is I've tested tons of other wires. Does anyone have a good power source under the dash that is hot in run and crank so that I can power up the relay?

Thanks!!

20190217_153937 by Jeremy Tepper, on Flickr

20190217_153908 by Jeremy Tepper, on Flickr

 

[jatepper]

So, I thought I had it figured out. Took out the ignition switch and found this terminal had power in both run and crank. So, I made a connection from this terminal to power / turn on the relay as the switched power source.

But, I'm still blowing the 14A fuse in the glove box. What gives??

20190217_165732 by Jeremy Tepper, on Flickr

 

[DirtDonk]

That center post is the ACC circuit so is hot in both ON and ACC, but it was my impression that it was "normally" not hot in START. But if you've tested yours and found it works, great!
Normally the only two circuits from the key that are hot in both ON and START are the Red w/green and the Green w/red wires.

What color is that Red wire that you originally tapped into?
Does that fuse have a label next to it saying what it is? After all these years I still don't have them memorized. Viperwolf (and probably a few others) have posted up diagrams but I can't find one at the moment.

And finally, do you have any pics of the relay? How is it wired so far?
You're correct in thinking that just switching it on and off should not blow a fuse. But maybe something else is at work here. Including even a bad relay perhaps. Never seen that happen, but it's possible.

Paul

 

[Viperwolf1]

Fuse #2 only supplies current to the turn signal flasher, windshield washer, original radio and backup lamp circuits. Hooking up anything to the stud on the back of the ignition switch cannot cause that fuse to blow. You have a different problem in one of those circuits.

 

[Broncobowsher]

What viper said.
Tugging and pulling on the harness to do your tap may have been enough to upset Zeus (Greek god of electricity) somewhere else in the harness.

 

[jatepper]

Thanks for the replies guys.

Why on earth does that fuse blow though when I'm taking my switched power source from the back of my ignition switch and using that to turn on the relay? Makes absolutely no sense. I'm normally decent with this electrical stuff, by this has my brain hurting.

 

[Broncobowsher]

IF you disconnect that tap, does the fuse stop blowing?

I screwed up a relay wiring once that was hard to figure out. when you hook up wires that should go to the coil to the contacts instead, weird stuff happens.

Back to the basics, Retreat until the problem stops and move forward slowly again.

 

[jatepper]

IF you disconnect that tap, does the fuse stop blowing?

I screwed up a relay wiring once that was hard to figure out. when you hook up wires that should go to the coil to the contacts instead, weird stuff happens.

Back to the basics, Retreat until the problem stops and move forward slowly again.

I'm going to tackle this again this weekend. Basically, I'm using a relay to power my Vintage Air AC/heater and my retro sound radio. I ran 10 AWG fuses direct from the battery to the relay (pin 30). I ran a heavy duty 10 AWG from pin 85 to a good ground. Pin 87 feeds both my Vintage Air (really just triggers that relay which) and the retro sound radio. Pin 86 is getting power on the ACC and run position, which is perfect. So, for this specific fuse to melt everything I hook up the switched power (back of ignition switch) to power the radio makes absolutely zero sense. My mind is boggled.

 

[Broncobowsher]

So if you unhook your tap, do you stop blowing the fuse?
Simple question that will tell if your tap is the problem or not. Until you answer that simple question there is no point in continuing this thread.

 

[Steve83]

That ScotchLok tap in your first pic is the WORST way to splice into a wire. It damages the source wire, and it's NOT a reliable connection anyway. This shows the correct way to tap a circuit:


(phone app link)

This shows (& the caption explains) how to add circuits to an early Bronco for nearly any function:


(phone app link)

 

[Timmy390]

I suspect the wiring on the relay is not correct. I'm powering 6 relays off a single source off the back of the ignition switch. No issues.......Runs my complete EFI setup.....

Tim

 

[Dannyboy71]

Did you check all your ground wires?

 

[jatepper]

So, I have it figured out....kinda.

I have a retro sound aftermarket radio. I unplugged the harness and the antenna from the back of the radio. Fuse did not burn up. I plugged in just the harness, fuse was fine. When I plug in the antenna to the radio that is when the fuse burns out.

So, I guess there's a short in either the antenna or the antenna cable? Still seems weird that the fuse that burns is the radio fuse considering the there is no power from that circuit going to the relay?!

 

[jatepper]

OK. Once again I'm stumped!

So I removed the antenna from the fender, plugged in the antenna cable from the radio to the antenna, and the fuse did not blow. Obviously the antenna is grounded once mounted on the fender. So, with the Bronco running, I grounded out the antenna mast and sure enough the fuse blew.

So obviously I'm thinking my antenna mast is bad, but what gets me is the fuse that keeps blowing is not tied up in to the circuit at all! I have relayed power going to the radio and the switched power for the relay is coming from the stud on the back of the ignition switch. With that being said, why is it that this fuse continues to blow?? This fuse one supplies power to turn signal flasher, windshield washer, original radio and backup lamp circuits. Original radio is long gone and I'm running a Retro Sound.

20190217_153908 by Jeremy Tepper

 

[DirtDonk]

I would not look at your antenna as the fault just yet. Since that power is not supposed to go through the antenna, there is a fault either in the radio itself, or something in that power circuit has shorted out to the antenna circuit somehow.
Not sure how that happens, but it's obviously happening or your fuse would not be blowing.

What happens when you leave the radio disconnected and ground the antenna?
Does grounding the antenna have any effect when the other end is disconnected from the radio chassis?

Paul

 

[DirtDonk]

And does this happen whether the key is on or off? Just on, right?

Paul

 

[jatepper]

DirtDonk - Good troubleshooting tip. I unplugged the harness going to the radio, left the antenna plugged in, and grounded the antenna and the fuse did not pop.

What are your thoughts now? When the radio is powered, it's sending current through the antenna and for whatever reason fuse 2 does not like it. Again, so confused because this is not even powering the radio!!

Only happens when the key ignition is on or in accessory.

Also, just for fun I removed the blinker and turn signal switch from the plugs to see if that had any impact on the fuse blowing when I grounded the antenna mast. It does not, so I imagine those circuits are just fine. I'm absolutely stumped. I don't think the radio is bad, but who knows!

Thanks for your feedback. Appreciate it.

 

[Broncobowsher]

Is this the antenna jack, or a wire marked "antenna"
If it is the jack, the radio is bad.
If it is a wire marked "antenna" that is a common wire used by most aftermarket radios. It is used to signal the power antenna motor to extend. Back when power antennas were a big deal. The wire is a hold out from those days. It is also used to as a signal wire to turn on external amps. So it should go hot when the radio is turned on. Hooking it to an actual antenna you are probably creating a dead short, and your antenna is probably bad as well.

 

[jatepper]

Is this the antenna jack, or a wire marked "antenna"
If it is the jack, the radio is bad.
If it is a wire marked "antenna" that is a common wire used by most aftermarket radios. It is used to signal the power antenna motor to extend. Back when power antennas were a big deal. The wire is a hold out from those days. It is also used to as a signal wire to turn on external amps. So it should go hot when the radio is turned on. Hooking it to an actual antenna you are probably creating a dead short, and your antenna is probably bad as well.

I'm plugging the antenna wire directly into the antenna jack on the back of the radio. So let's pretend the radio is bad...why does fuse 2 (turn signal, back up lamps, and radio ***RADIO IS NOT POWERED THROUGH THIS FUSE***) keep blowing? This still just makes no sense.

 

[Steve83]

why does fuse 2 (turn signal, back up lamps, and radio ***RADIO IS NOT POWERED THROUGH THIS FUSE***) keep blowing?

There are several possible reasons... You might not WANT the radio to be powered through that fuse, but it MIGHT still be somehow. We can't see all the truck's wiring to check, so either you have to check, or you have to find someone local who can check for you. Another possibility: something ELSE powered by that fuse is grounding through the antenna. Check all the body grounds. There should be at least one from a welded (not bolted) piece of sheet metal (like the firewall, core support, or inner fender) directly to the battery (-) post.