short in horn in 85

[true74enduro]

i took my truck in to the shop didnt have the time to fix a bad bearin column. so i told my mechanic to fix colum, and see about fixing the horn because it was just on a push button. well come to find out he replaced the horn parts but still nothing. theres a short some where cause when you put in a fuse in the horn slot it bursts the fuse! any ideas or test i could do

[old Rusty C10]

you gotta trace the wires back from the horn itself. there is somewhere where a power is touching a ground. You can first unplug the horn itself and replace the fuse and see what happens but if there is a pushbutton to that h orn chances are the horn is good , and make sure that there is in fact only one horn or that both horns are plugged into your pushbutton . if the fuse says good its prolly the horn otherwise take an inlne fuse and length of wire and connect that to the interior part of the fuse panel to the unplugged horn and see what happens. This will eliminate the area from the column to the fuse box as a source for the short there, If that doesnt yield results, you need to go through the wiring in the area between the fusebox and the column..with a test light and lastly if the thing doesnt work you need to figure out whats wrong in the column

[true74enduro]

thanks for the help ill try messing with the thing tomorrow

[true74enduro]

Anyone here happen to know where the grounds are for the horn on these trucks?

[03glide]

Did you get it fixed? Having an issue blowing the same fuse.

Brian

[true74enduro]

Sadly I spen a while tracing the wire and no such luck on fining a wire touching a ground. From what I was told sense mines an 85 k10. The dome curtassy lights cigarette glovebox are all connected. I opened up the dome light I thought I found the problem. The positive and negative wires had melted together. I then fixed that problem and then insured that run of wire was good the rest of the way. Next I went sill plate to fuse block. Looks fine to me. Then I went to the cig lighter I think I found the problem there. Do the cigarette lighters go out? Causing a short? It has to be either that or some where in the column.

[true74enduro]

This is another post I did and I followed the guys advise. Question is the Orange wire from the dome does it connect to the back of the block or the top that's how mine looks like it's hooked up. Who know i probably had to separate electrical problems on the same curcit.

[03glide]

Thanks. I'm going to pull it apart tonight.

[true74enduro]

A place you might also check is the courtesy light switches in the door jams as those I know are a known problem for our trucks

[true74enduro]

Originally Posted by old Rusty C10

you gotta trace the wires back from the horn itself. there is somewhere where a power is touching a ground. You can first unplug the horn itself and replace the fuse and see what happens but if there is a pushbutton to that h orn chances are the horn is good , and make sure that there is in fact only one horn or that both horns are plugged into your pushbutton . if the fuse says good its prolly the horn otherwise take an inlne fuse and length of wire and connect that to the interior part of the fuse panel to the unplugged horn and see what happens. This will eliminate the area from the column to the fuse box as a source for the short there, If that doesnt yield results, you need to go through the wiring in the area between the fusebox and the column..with a test light and lastly if the thing doesnt work you need to figure out whats wrong in the column

awesome I'll try and figure it out soon as it snowed a lot here and it's colder then crud. I did have one of the horns hooked to a push button and then linked to another interior fuse. I'll have to test the other horn to see if it's not the problem.

[03glide]

The wire for the cigarette lighter housing was grounding against the ash tray.

[true74enduro]

Od I don't recall mine being grounded to my ash tray. Could please post a picture of yours maybe it will help me Out

[03glide]

Its not supposed to be grounded. That is what was causing the fuse to blow. It had come off of the housing and was resting against the ashtray.

[true74enduro]

alright well on my truck I needed to Change my battery terminal cables, while doing this I ran a new wire from the battery to my CD player. Well I thought I'd see if my cigar lighter was being grounded out like I thought it was. Well I ran a pig tail from my cigar lighter to the hot wire I ran as soon as I did that they sparked. this was a sigh of relief think that I found part of my problem on my truck. Now sense there's no more light out and I can't work on my truck I'm hoping I found the only problem as to why my horn,cigar, dome and curtassy lights aren't working.

[77c10]

Originally Posted by 03glide

The wire for the cigarette lighter housing was grounding against the ash tray.

It's almost always something simple like that.

[true74enduro]

When the fuse blows, can it also blow the relay to? I know a fuse should protect it.

[true74enduro]

Alright so I changed out m cigar lighter and it was only part of my problem in my short. This is a link to a thread I posted on the 73-87 forum and shows also what I've done.http://forum.73-87chevytrucks.com/sm...?topic=30040.0 K so I guess I'm gonna go back threw my truck and work backwards to trace my problem. This is a scren shot of a post I found. Is this an accurate way to test and see if the shorts in my column or not?

[hatzie]

Download the 1985 GM Factory wiring diagrams. See below..

There are only two systems on that fuse. The horn and the lighter. The dome and footwell lamps are on Circuit #40 and are fused elsewhere.

The horn button grounds the electromagnet in the horn relay so if that wire were shorted the horn would activate. Don't ask...

There are two circuits in the hot side of the horn output and power feed.
When are you blowing the fuse... Immediately when you plug it in (power feed) or when you push the horn button (output)?
The answers will isolate the circuit to trace.

If you are blowing the fuse when you push the horn button your short is in the output side between the horn relay and the horn. Trace GM Circuit #29;

• Dark Green from the horn relay to the bulkhead plug in the cab.
• Black/Green from the bulkhead plug to the horn in the engine compartment.

If the fuse blows immediately... Your trouble is on the Power feed side. It's GM Circuit # 240 Orange wire that's entirely inside the cab;

• The orange lighter wire should be to the centre pin of the lighter socket. If you somehow managed to hook this to the side terminal it's grounding on the dash.
• The lighter power wire daisy chains from the fuse through the horn relay coil-power/common terminal on the fuse-relay block to the lighter. If you have a short in this wire it'll blow the fuse.
• The $5-$10 Horn relay could be the problem. AC Delco D1776 or Standard Motor Products HR151. I've seen the spring terminal break off inside a relay and rattle around inside the case. Unplug it and see if the fuse still blows...

[true74enduro]

Sorry thought I listed model and year. Its a 1985 Chevy k10 lwb 305 with 700r4. Awesome thanks for the input. My horn fuse blows instantly when being installed.

[true74enduro]

Originally Posted by hatzie

Download the 1985 GM Factory wiring diagrams. See below..

There are only two systems on that fuse. The horn and the lighter. The dome and footwell lamps are on Circuit #40 and are fused elsewhere.

The horn button grounds the electromagnet in the horn relay so if that wire were shorted the horn would activate. Don't ask...

There are two circuits in the hot side of the horn output and power feed.
When are you blowing the fuse... Immediately when you plug it in (power feed) or when you push the horn button (output)?
The answers will isolate the circuit to trace.

If you are blowing the fuse when you push the horn button your short is in the output side between the horn relay and the horn. Trace GM Circuit #29;

• Dark Green from the horn relay to the bulkhead plug in the cab.
• Black/Green from the bulkhead plug to the horn in the engine compartment.

If the fuse blows immediately... Your trouble is on the Power feed side. It's GM Circuit # 240 Orange wire that's entirely inside the cab;

• The orange lighter wire should be to the centre pin of the lighter socket. If you somehow managed to hook this to the side terminal it's grounding on the dash.
• The lighter power wire daisy chains from the fuse through the horn relay coil-power/common terminal on the fuse-relay block to the lighter. If you have a short in this wire it'll blow the fuse.
• The $5-$10 Horn relay could be the problem. AC Delco D1776 or Standard Motor Products HR151. I've seen the spring terminal break off inside a relay and rattle around inside the case. Unplug it and see if the fuse still blows...

Just making sure circuit 240 should be where my problem is. I maybe my wiring diagram for my 85 isn't correct I don't see #240 I see #140.

[true74enduro]

Sorry I didn't realize I forgot my year make model. It's a 1985 Chevy k10 lwb 305/700r4.
My horn fuse blows as soon as it is installed. Just making sure you said circuit #240. I only see #140.

[true74enduro]

Other pic

[ray_mcavoy]

Originally Posted by true74enduro

Just making sure circuit 240 should be where my problem is. I maybe my wiring diagram for my 85 isn't correct I don't see #240 I see #140.

Download the factory wiring diagram that hatzie recommended from his signature and you'll be able to find circuit #240.

The ones you have pictured appear to be the "typical" / "generic" diagrams from an aftermarket Haynes or Chilton type manual and are not as detailed as the factory diagrams.


The Horn fuse also protects the BATT receptacles up above it in the fuse box. So if you have any factory or aftermarket accessories plugged in there, check them and their wiring for shorts to ground too.

[hatzie]

The only factory accessory plugged into the fused Batt positions is the optional clock.

Your first slide looks like a MOTOR manual. The others are from the Haynes manual. One size does not fit all... RTFM

[true74enduro]

Thanks a lot Hatzie for the help in what to do on my truck and to all the others. I'll let yall know what was wrong in the wiring.