Having some trouble locating a wiring problem.

[colbystephens]

So I have a short in my horn circuit, which also happens to be my interior light circuit on my '90. I also have simply plugged into an accessory port for my CB there. Finally, it seems the previous owner did something with regard to the stereo on an accessory port, so that is affected as well. The accessory ports I'm talking about would be represented by the "c" bank below.


Wiring-7 by colbyjstephens, on Flickr

I'm sort of a newbie to wiring diagrams. The lower left of this diagram, from the slosh page, indicates some sort of connection on the fuse block between the Horn/Dimmer, TA/CTSY, and a 10A fuse below it.

1. Should I be looking at all three of those circuits for the short, or just the Horn/Dimmer circuit? I have pulled the grille off and looked at the horn wiring, which is good. Also, disconnected them, the stereo, the CB and pluged in a fuse which immediately blew.
2. What is the TA/CTSY circuit and the 10A circuit below it? I can't decipher that acronym. Perhaps they're related? Edit: Looks like that is likely the dome light fuse, so the 3 fuses seem related?

To my knowledge, only the Horn/Dimmer fuse is blown, but the truck is at the exhaust shop, so I can't confirm till tomorrow.

Finally, I'd like to make sure to wire up the radio properly. The PO used the existing power for the stereo, so I'm not sure what the little wire running to an accessory port does. Ideas on this?

 

[p0ps45]

"TA" is actually "T/L"= tail lamp. CTSY is the underdash courtesy lights, underhood light, glove box light.

You can try to test by pulling the horn relay and see if the fuse still blows. The dome light(DM) is also powered from the same fuse as the horn through one of the c connections.

All these circuits are turned on and off by grounding, so it sounds like you have a hot wire grounded to metal because the fuse blows instantly. You may have a bad wire in your steering column.

And now that I probably have you totally confused I can get you pics of the wiring diagram tomorrow that shows the circuits from the back of the fuse block.

 

[lectric80]

The three fuses are loosely related by the fact that they are all constant hot circuits. The link you see is basically linking them all to the battery hot side of the fuse box, but they are not truly linked as it appears in the diagram.

If you are blowing the Horn/dimmer circuit, it is possible that the problem is the dimmer switch on the column, or it is the horn relay/wiring. You can unplug the dimmer switch, or the relay, and then replace the fuse to see which is the problem. If neither solves the issue, it is likely going to be a power wire that is broken and grounding on metal. The horn relay seems more likely, based on the majority I have seen being under the hood on our trucks, so check the power wire running to it from the fuse block. There are no wires running through the column related to those circuits except the ground wire for the horn, which would just make your horn sound continuously.

As for the stereo tie in, I would need to see a pic of the wire you are looking at, but I am going to guess it is the stereo memory wire, since many of our trucks didn't have a constant hot running to the stereo for the memory. It is very likely based on the C portion of the fuse box, which is constant power area IIRC.

 

[mpio13]

Sounds like a short to me. I have blown this fuse before, but honestly, I just popped a new one back in and didn't worry about why it blew, which I know I should, I just haven't looked into it yet. (hasn't popped again, either, in 7 months)

Anyways, sounds like a short. Fuses pop when too many amps try to rush through it. (obviously they're rated in Amps) so whether its a grounded circuit controlled by power or a powered circuit controlled by ground, when a wire shorts out the circuit suddenly closes but has too much resistance via the short, and the amps spike, popping the fuse.

I'd agree that the relay could be the problem, but you said you replaced the fuse and it blew instantly, right? That makes me think its shorted out. The relay would probably only pop the fuse when you hit the horn (activated the relay)

If you have a multi meter I could run you through a couple tests that've been pretty helpful to me locating shorts.

 

[brian wafer]

if you think it has something too do with interior lighting! i,ve seen problems where ,i beleive its an orange wire . which runs under the carpet might be grounded by the door sil screws.

 

[colbystephens]

Thanks for all the good info!! A couple of extra notes I thought about:

1. I've never had under-dash lights working in this truck. Didn't know there were any! I'll have to check that fuse too.

2. It used to be that the fuse would blow every couple weeks. I'd put a new one in, it would work fine for a while and then blow. Now, I can't even put one in without it popping. Additionally, you would suppose that the stereo would work if it wasn't somehow directly related to this circuit. In the past, I've had an issue where the stereo would stop, but if I shook the wires under the dash, it would often work again. If not, wait a couple days and it would straighten itself out.

I think I have some wire tracing to do. Uggh.