ericgrau

iTrader: (1)

I have a problem that I suspect is caused by the horn relay. When I try to honk the horn I hear a click but no horn. Sometimes in the winter the horn works. So I checked the FSM and my Haynes manual and couldn't find anything horn related at all. Where is the darn thing?

HAILERS

Inside the CPU like the free online diagrams show and it's also shown in the ENGINE ELECTRICAL section (that might be BODY ELECTRICAL I forget). Series four cars.

Stop fuse powers the relay and horns.

It's just like the jpg attached. Pull the plug off the CPU. Jumper the GW wire to the GR wires in the plug. Honk honks if it's got the wires on 'em. Proves the fuse is good. Push the horn button to honk, with all plugs on the CPU. HEar a click. Horn relay pulling in, proving the gnd to the relay and power to the relay is good.

Or leave the plug on the CPU and with a piece of wire connected to gnd on one end, and the other end put up the backside of the GW wire, relay pulls in and horn honks.

ericgrau

iTrader: (1)

Thanks, that helped a bunch.

Everything hooked up, pressed horn button, no click nor horn. Dunno if it stopped clicking today or a long time ago. Jumpered GW to GR on the plug and horn honked. Checked all interior fuses and they're good. Grounded GW to chasis with a wire with everything hooked up and also no click nor horn.

So I need to open up the CPU and deal with the relay? How do I get those tabs off? They didn't seem to budge against my flathead screwdriver. Push harder? Take it to a dealer or mechanic like the Haynes manual says?

beefhole

iTrader: (29)

I've read also that the actual horn button/contact in the steering wheel can also corrode and create problems. It's often overlooked, but try cleaning those too.

HAILERS

************************************************** ************************************************** ************************************************** *

OOPS! Another one of my ERRORS. You put a ground on the Green/Orange wire with everything connected up. Relay pulls in and horn honks.

I fear I made you blow your STOP fuse in the interior if you put the grounded wire to the GW wire. Sorry 'bout that. It shoulda blown if GW gets a gnd put on it.

See the jpg in the other post I made and how the G/O wire comes from the steering wheel buttons.

Make sure your STOP fuse is good before trying again. And to assure the STOP fuse is still good, just jumper the GW to the GR like you did before to make the horn work. Or step on the pedal and look for the stop lights to come on, proving the fuse is still good.

Terrapin_turtle

iTrader: (2)

I just fixed my horn the problem was bad solder joints in the cpu took like 15 minutes and now it works perfect. Look through the archives there is a brief write-up.

ericgrau

iTrader: (1)

So I just fiddle with the plastic tabs longer to get them off?

Scary, I hope I haven't been driving without stop lights. I'll check that fuse soon. That may be why the relay isn't even clicking anymore.

HAILERS

That may be why the relay isn't even clicking anymore.

Yup

ericgrau

iTrader: (1)

Stop fuse looked fine. Replaced it anyway. Still no clicking with CPU installed. After that I removed CPU to take it apart. Stop lights not working, but that's probably b/c I removed the CPU?

For those doing a search, its a million times easier to pry at the edge of a panel near the tab rather than pushing on the tab itself. Use a thin screwdriver or similar small flat object.

So I got the thing apart and all 4 relays seem perfect. Voltage applied to the coils cause all 4 to click. Manually closing the relays and checking for conductivity tested good on all 4. And they look clean as a whistle, including the contacts.

Great, so now what do I do? What are the common failure points to resolder/replace/etc.?

ericgrau

iTrader: (1)

Tested it with the board in the car. At first pressing relays had no effect. Then tugging on the cable made everything work: pressing relay honked horn, pressing steering wheel also honked horn. So do I clean the contacts on the connector or do I redo the connection between wire and connector? Use contact cleaner or a file? I have both.

As long as I have the CPU open, would any part of it be related to my reverse lights? Which plug? Those don't work either. Meh, either way I'm just gonna spray every connector with contact cleaner now.

beefhole

iTrader: (29)

Reverse lights are switched from the transmission.

HAILERS

Reflow the solder at the contacts where the harness plug mates with the jack on the board.

It's not the electrical plug on the hareness, but the prongs/jack that the plug mates with. Reflow the solder to each of those *prongs*.

ericgrau

iTrader: (1)

Ugh, and I just put it back together too. Okay, I took it apart, sucked off the old solder and re-soldered all the joints on the plug. Horn still works. Thanks for the help.

Gonna check my stop lights when it gets darker out. As long as I have my soldering stuff out i'm gonna give my logicon another shot. I tried just the connectors before but there were other cracked joints too, and I'm not sure how well they were soldered. I may just re-solder everything.

Thing is, this is my 2nd logicon and I'm having the exact same problems as the first: heater air control doors won't move, and the vent selector won't work either. Blower speed control, A/C switch and inner/outer air source control work fine on both logicons. I briefly tried a 2nd faceplate, but that one is missing the heater slider and the vent selector didn't work on that one either. The heater air control failed slowly; it used to work intermittently, sometimes sticking on whatever setting it was last on. After I tried swapping logicons it failed for good, even after I swapped back. It was stuck on cold so I tried leaving the slider on the hot setting for a while. Eventually it switched. Unfortunately it's now stuck on hot, so I gotta leave my blower off. The vent selector was bad before I bought the car.

Terrapin_turtle

iTrader: (2)

I've had to resolder like three different things, I think the heater control could use some love as well, Mazda don't know how to solder...

StevenL5975

Just to revive a dead horse. Today I found that my horn isn't working so I searched and found a few threads.

I have a 1987 S4 NA, EU version.

• Both horns do work if I hook them up to 12 Volt directly
• Both relays in the CPU click when I push the horn button
• Jumpering the Green/White and Green/Red pins on the upper CPU harness plug does nothing. No honk.
• Checked conductivity and soldering joints on the CPU relays -> All fine!
• STOP fuse is working because I have stop tail lights working.

Any pointers? I have checked everything that I could but still no horn ...

Brgds
Steven