1985 Ford F150 Lariat
302-V8

I was doing some housecleaning under my hood to get rid of all excess wires I don't need anymore after converting from EEC-IV/TFI to Duraspark II ignition. Working from the engine compartment, I was cutting wires to take the computer out and found I accidently cut all the wires in the engine compartment that connects to the horn relay under the dash!

Here are the loose/cut wires coming from the horn relay under the dash:
1. A thick YELLOW (fusible link) wire that goes to the starter relay and it has an eyelet for it. (which post?)

2. A RED wire that I have no idea where it goes.

3. A BLACK wire that has GREEN dots along the wire, and I don't know where this goes.

4. A YELLOW wire with blue/green hash marks on it goes to another plug-in connector located in the engine compartment on the inner fender on the driver's side. (This connector plug has another cut wire that is red with a blue stripe, anyone know where this goes? Surely Ford coded these wires with colors for a reason, right?)

The only things that went out are:
1. Horn
2. Cruise control
3. Courtesy lights (under the dash)
4. Tachometer suddenly started reading too high

Can someone please help?

 

The yellow/lightblue is the power feed for the horn and the cruise buttons and the cigarette lighter. It goes to fuse #4 in the fuse box.

The black/lightgreen is the power feed to the wipers. It comes from a splice that leads to the ignition switch.

The large yellow wire is a main power feed wire.

Red with a blue stripe is the start wire that goes to the starter solenoid.

Looks like you have cut way more than the horn wiring.

 

Thanks for your response, Franklin.

Something's not right, because I didn't cut ANY wire to the fuse box. I ONLY cut wires under the hood.

However, it appears that there is a plug-in connector that has three wires going into it from the firewall on the driver's side. The other end of that plug-in connector, located on the inner fender (NOT the ignition module plug-ins, although it is the same type of connector), has only two wires coming off of it which I accidentally cut. One of which is yellow w/light green hash marks and the other is red w/a blue stripe. I assume the yellow w/light green hash marks connects to the horn relay?

My horn relay, located under the dash in the cab, doesn't have ANY wires going directly to any fuses. All 4 wires that go into the horn relay go directly through the firewall and into the engine bay. That is where they were cut.

My wipers work fine. The wire is black with dark green dots.

That makes sense. On my truck, this wire is a fusible link. I guess that is why the horn stopped working.

Start wire? But my truck starts great! Did I forget to wire up something else that has to do with the ignition?

What about the RED wire that comes out of the horn relay and routes through the firewall?

It may be easier to find out what exactly has to go through the horn relay to work?

The only things that are out are:
1. Horn
2. Cruise control
3. Courtesy lights (under dash)
4. Tach is reading too high

 

Ever consider soldering the wires back together?

 

Before I removed the EEC-IV wiring harness, I hooked up the Duraspark ignition, and drove my truck for about a year and EVERYTHING worked great. Then I decided one day to clean up under the hood and get rid of all the extra wiring I no longer needed. I would cut the wires I didn't think I needed one at a time and then check to make sure that all of my equipment(like lights, signals, gauges, etc.)still worked and the truck would start.

I simply forgot to check operation of the horn, and didn't notice the courtesy lights, and now I know the cruise works along with the horn. The tach works fine at all speeds including idle, only when it goes into overdrive is it registering too high. The horn relay is located right beside the computer under the dash, and I originally thought it was part of the computer and that is why I cut those wires. Sounds like a pretty honest mistake, right?

When I cut out that HUGE MASS of wires that powered the EEC-IV computer, it seems that the wires I cut that was still needed was intertwined with the computer somehow. Or at least they went through the computer before going to what was actually needed.

So what do you think? Any idea where the RED wire and the black wire with dark green dots that come from the horn relay go to in the engine bay? And what about the red wire w/blue stripe that goes to the starter relay? Why does my truck still start fine if I need that wire?

 

I haven't a clue about the red wire. There is no red wire going to the horn relay in the schematics. I thought the horn relay was located over near the driver's side kickpanel under the dash?

 

My horn relay is located under the dash to the right of the steering column, and is attached to a brace that holds the EEC-IV computer in. There is grommet that the wires from the horn relay (and the computer wires) go through to get into the engine compartment. The horn relay has (4) cut wires:

1. Black w/green dots
The black wire with green dots comes out of my firewall on the driver's side (where the steering column is) into a plug-in connector. The other end of this connector has TWO wires coming out of it: one is GREEN, and that one goes to the coil, and the other wire is black w/green dots.

It appears that this wire goes through the firewall again (through the rubber grommet that the horn relay and computer wires go through) and to the horn relay, because the horn relay has a cut wire that is also black with green dots.

2. Yellow w/blue hash marks
A different plug-in connector coming out of the firewall on the driver's side has three wires going into the connector, and two wires coming out. One of the wires coming out is yellow w/light blue hash marks, and the other is either RED (see 3. below) (or is it red w/ a blue stripe? It's hard to tell)

It appears that the yellow wire w/light blue hash marks goes through the firewall again and to the horn relay as well, because the horn relay has a cut wire that is also yellow w/light blue hash marks.
This must be the horns?

3. RED wire
(See 2. above)The RED wire (or is it red w/ a blue stripe) I still don't know, but I do know that the horn relay has a cut wire that is RED, so it may connect to that?

4. Thick Yellow wire (fusible link)
This wire comes straight out of the horn relay, and connects to the battery side of the starter relay on the passenger's side fender.
This must be the power to the horn relay.

As for the tachometer, I did a search last night and found out that if a factory tachometer is being used with a V8, the the tach has to be grounded, or else it will read too high. (An I-6 engine doesn't use a ground wire.)
That explains my tach reading too high.

Someone suggested that the tach is grounded through the distributor if using stock Ford parts (which I am). Is there a seperate wire for grounding the tach? If so, where is it grounded?

Is the horn relay supposed to be grounded as well?

Sorry, I don't understand electronics at all, and I don't really understand what "grounded" means.

 

I am thinking that you are not working with the horn relay, but are actually messing around with the old EEC relay that powered the old computer. The EEC relay does have a red wire, and the other wires seem to match too.

The grounding part of the tach is just a seperate wire on the back of the tach that is grounded to select 6 cylinder or 8 cylinder. Grounded means the terminal or wire is connected to the - of the battery. Of course the - of the battery is connected to the engine block and sheetmetal, and all of this is called a "ground".

I believe you are going to have give yourself a crash course on reading diagrams, and get yourself a Haynes manual. For your year truck, they have very good diagrams in the back. It has all the info you are looking for. If that seems over your head, maybe you can get someone to help you.

 

This the power wire for the horn relay and the power to the speed control via the horn relay coil.
It runs from the horn relay to fuse #16.

The horn relay should have three wires to it:
DK BLU -- Coil to brush in wheel to supply power to speed control/ground horn
YEL-LT BLU -- to fuse #16
YEL-LT GN -- to horns

This is why your horn and speed control does not work.

There should have been a light green wire with yellow (stripe/dots/hash?) running from the headlight switch (fuse #8) to the door switches and on to the Instrument Panel courtesy lights (a black wire with a blue stripe here).