Honk and Wipe: Volvo Horn Button Fun

One of the Volvo's favorite tricks is to turn on the rear windshield wiper when the horn button is pressed. Sometimes the horn can be tricked in to sounding by pressing hard on the steering wheel on one side or the other.

This is a known issue, stemming from a grounding problem in the wheel. The steering column has several joints that can telescope and move, so that if the car is in an accident, the driver won't be crushed by the steering column. The electrical connections in the joints seem to be poor.

A pesky grounding problem, at that. I spent half an hour with a set of gator clips and could not conclusively determine the point of fault. A contributing factor is that the 1990 Volvo 740 does not use a horn relay, instead controlling the entire current need to drive the horns (did I get 3 amps on that, Kenny?). A weak connection that shows conductivity may actually be resistive under load.

The circuit is a bit unusual because the horns always have +12 volts, and pushing the horn button completes the circuit.

The maddening thing is that a working horn is -required- to pass Virginia Safety inspection. (To be clear, the inspector has always managed to make the horn blow and thus the car has never failed because of it. That said, the horn sometimes refuses to blow (though the rear window is very clean, thanks) for me when I conduct random inspections.)


Chimera.

I wanted a little red button to blow the the horn that looks like this:

Thus, I went about making a horn-always-passes-inspection button. I decided to put on a blank plate that resides in the bank of switches to the left and right of the steering wheel. I went to Radio-Trash, and purchased a large, red button and some wire taps, popped the blank plate out (it has to large tabs holding it in), and then did some precision drill work on the floor of the basement.

 Pretty much everything you need to get your beep-beep on.

Precision drill work:

I took the horn, installed in the switch plate, with two thick wires soldered on, back to the car and popped it into the dash.

The electrical connections proved to be a bit of a rats nest, because the color of the horn wire is not clear in the Haynes book (brown and yellow or brown and blue, or is it blue and brown?!). The cowel comes off the steering wheel cover quite easily, so I traced the horn wire back to the contractor. In this car, it's blue and brown. It's the wire connecting to the center of the spool shaped contractor.

A view of the underside of the steering wheel. There turn signal cams are visible here, and it's more obvious why the wipers go when the horn button is pushed... the various switches and stalks all live in the same assembly.

I attached a tap to the horn wire on the big block connector (left) and then choose an handy black ground wire and tapped the other lead. Pushing the button closes the circuit, allowing current to flow through the horns.