Hi All,

I am trying to fix my horn/cigarette lighter/cruise control problem. When I bought the truck in August 2019, the horn and cruise did work. I have since done a lot of work to it. It is eating through 20amp fuses.

Here is what I have done:

- verified 12V at the fuse block
- pulled cigarette lighter, determined it to be in-op and replaced with new cigarette lighter
- pulled cruise relay and tested for voltage (nothing with ignition off, 0.15V with ignition on)
- tried jumping wires on cruise relay connector (no response)

I pulled off the horn pad and ironically as I was pulling it off, the horn sounded once and then blew my last 20 amp fuse. What is really strange is the horn blew while the relay was disconnected.

Any suggestions on where to go from here? I read on some of the threads about jumping wires under the hood pad, but I am not sure of which (yellow and blue?).

I ordered a box of 20amp fuses from eBay which should be here next Saturday.

Thanks,

h.ubk

 

What does this 20a fuse serve?
Does it serve all that you posted, horn, lighter & cruise?
If so disconnect all of them from the truck. Unplug the horn(s), remove the wire off the back of the lighter & if your cruise is the same I just saw I think there was a plug at the unit under the hood.

With all this disconnected does the fuse still blow? If so you now know the issue is in the harness and not the disconnected units.
Good luck on hunting down the issue.
Dave ----

 

The 20A fuse is for horn, cigar lighter, and cruise control. Without using any of the accessories, the fuse will not blow.

It blows immediately when I touch the horn and it blows intermittently if I try to plug a USB charger into the cigar lighter.

So, it sounds like it is probably not a harness issue.

h.ubk

 

I would still unplug everything and only plug 1 thing at a time.
Plug in just the lighter and try the USB port and see if it blows the fuse.
BTW you can get a 20A beaker that should plug into the fuse holder and instead of blowing it trips and then resets.
If the fuse dose not blow unplug lighter and plug in the horn and give that a try.
Did not blow unplug and plug in the cruise and see if it blows.
If it does not then I would plug in say the lighter with the cruse and check and so forth.
Dave ----

 

Have you found the horn relay?

 

A partially broken wire will add enough resistance to overload the circuit. Check the power source at the start of the horn/cigar lighter circuit.

 

I don't remember ever seeing a relay for the horn on either of my 81 trucks and I had the whole wiring out of both to swap in to the project truck.
Dave ----

 

What model year?

 

Horn relays are used with cruise control.
He has an 1986.
Photo here of the relay ...
https://www.ford-trucks.com/forums/1...l#post17771445

Be sure to read the whole thread.
JIm

 

Hmm, this tidbit makes me think you had a different relay disconnected.

Wiring diagram here:

Horn & Cigar Lighter - Gary's Garagemahal (the Bullnose bible)


I'm not seeing any way the horn could sound if the horn relay was unhooked.

I'd also suggest putting a paper bag over your head and picking up one of the doohickeys at Harbor Freight:

https://www.harborfreight.com/30-amp-automotive-fuse-circuit-tester-67724.html

This takes the place of the fuse and lets you read amperage directly. I have one and it works great.

 

With Speed Control, the horn relay is located on the Speed Control amplifier, located under the dash adjacent to the steering column..

1978 and later: No Speed Control, no horn relay!

 

I did read the WHOLE thread but I did NOT know the horn used a relay on ONLY speed controlled trucks.
Sorry
Dave ----

Thanks Bill I learned something today.
Would you know if they used the relay because with the speed control & horn it over amped that fuse?
Dave ----

 

Some progress today. If I jump the two connectors under the horn pad, the horn will sound. This is with the relay disconnected (see below pics). If I reconnect the hood pad, the fuse blows immediately. The fuse blows immediately if I connect the USB charger to the cigarette lighter.

h.ubk

 

Ok tell us how the horn could blow and not have the relay plugged in?
That relay can not be fore the horn but something else but what?

Now you are saying for the horn touch wires together it blows but if you hook them to the pad it blows the fuse?
Is the pad installed in the wheel or out when this happens?
If you check for power on the 2 wires I would guess 1 is out and the other not.
The not then has to be the wire out to the horns and when the pad is installed it shorts the hot wire to ground and blows the fuse.
Dave ----

 

I don't know. I was wondering that myself. The truck has had two previous owners. I have no idea what they may have done with it.

Yes, that is correct.

The fuse blows when the horn pad is installed and I press it and also when it is just dangling out and I press it. I also tried connecting the black wire to a different ground via alligator cable and it still blows the fuse.

You would be correct.

h.ubk