If you've just picked up a set of trumpet horns for your 1963-65
Riviera or 1964-65 full-size Buick, you may find that they don't work
real well (if at all). The horns frequently suffer from
accumulated corrosion inside, which impairs their ability to operate
as intended. The fix is a complete rebuild. The procedure is
described below. Information about the wiring
harness is at the bottom of the page.
* There are identifying numbers stamped into the flange of the
trumpet base. These numbers correspond with the last 3 digits of
the GM part number (group 2.810, part number 1999xxx).
** The 1965 small horn was superceded with the same small horn that
was used in 1964.
The first step is to disassemble the horns. The actuator and
the trumpet are attached with pop rivets. You have to drill
these out. Use a 3/16", 13/64", or 7/32" bit. Drill out
enough meat to get to the level of the mounting flange, then knock the
rivet out with a punch.
After the horns are apart, you'll probably find that the diaphragms
are covered with rust and scale. This is the root of the
problem, as it prevents the diaphragm from vibrating properly. There
may be rust inside the actuator and on trumpet mounting flange as
well. This has to come off.
Look here for some tips on effective rust removal. If you
have severe damage to either the diaphragm or the actuator, they may
not work even after they have been cleaned up. These parts are
the same in all large diameter GM horns of the era; the only unique
part is the trumpet itself.. Find some cheap donor horns (they're
stamped Delco Type-S) and cannibalize them.
Now that the old paint and rust have been removed (notice how I
gloss over that part), you need to a) perform a little routine
maintenance, b) do what you can to prevent a reoccurrence, and c)
reassemble the horns:
The only maintenance is to clean the points. I first pried
the points apart by inserting a screwdriver and gently twisting, then
I slipped a piece of emery cloth between the contacts and pulled it
across. Be sure to do this for both the upper and lower
To limit the likelihood of rust forming in the future, I painted
the horns with a rust-inhibiting primer. I painted all of the
trumpet (the horns and both sides of the mounting flange), both sides
of the diaphragm, and the outside of the actuator and the mounting
flange. I chose not to paint the actuator circuitry so as not to
interfere with the points or the solenoid. I also made new
gaskets to keep moisture from entering between trumpet and the
actuator shell. I used a 12"x12" sheet of 1/16" gasket material. There
were two problems with using thinner material:
- The flanges aren't perfectly flat. A thinner gasket won't seal.
- If the material is too thin, it repositions the diaphragm in
relation to the points. This distance is critical for adjusting the
operation of the horns.
For cosmetic reasons, I reassembled the horns using 3/8" 10-32
and toothed washers. I found that 1/2" screws were a bit too long, as
the nut would have bottomed out. After repainting the horns,
it's not immediately obvious that the horns have been repaired.
You might also consider using
Stover nuts, or conventional nuts and lock washers;
nylon lock nuts may deteriorate at the temperatures found under
Now that the horns have been put back together, you need to adjust
them. The head on the adjusting screw is, to my knowledge, not
used anywhere in the world other than on GM horns. I used
narrow-head (needle nose) vise grips to turn it. Insert the
adjustment screw, turn it until you start to feel resistance, then go
about one more whole turn. This is a good starting point.
Hook up a 12V supply to the terminals, then turn the screw until you
get good tone. If you go too far, the horn will start to
"sputter". If you go further still, the horn won't work at all.
The easiest way to do this is by using an ammeter to measure the
current draw. If you're using a battery charger as your power
source, you can use the integrated ammeter. Turn the screw in to
decrease current; back it out to increase current. According to
the shop manual, you want to draw between 9 and 11 amps, or a 7-11
volt drop across the horns. NOTE: If you supply the power
to the horns by directly touching the leads to the power terminal or
horn body, you will pit whatever you touch. It is better
to put a spade lug on a length of wire, then connect the power to the
other end of the wire.
There is no way to "tune" the horns. Adjusting the current
draw will change the volume, but not the pitch. See the earlier
table for the intended pitch. The actual pitches on my 1963
horns are C# and A for the large and small horns, respectively.
There's nothing left to do but repaint the horns and install them
in your car. I painted mine with Krylon semi-flat black.
Any kind of semi-gloss black paint will do.
A second-hand set of horns is probably missing the wiring harness.
You can make this harness yourself. An illustration in the shop
manual shows the correct routing of the harness and the position of
the connectors in the harness. If you are particular about having the
correct colors for the wire, contact
Rhode Island Wire The carry the proper black with blue
tracer wire that you need for the power lead. They also carry
the required connectors and plastic shells. Based on the wiring
specs for the standard horns, you will need to use 12-gauge wire.
If you're not that particular, get automotive wire and use standard
spade terminals. NOTE: Standard wire (e.g. from Radio
Shack) is not designed to withstand the heat and solvents under the
NOTE: The illustrations in the 1964 Buick Chassis Service Manual
(Figs. 11-186/7) are incorrect. The power lead to the horns
needs to tap into the green wire from the horn relay. The
illustrations show the lead coming from the black wire. This
will bypass the horn relay entirely. It will route the horn
current through the horn button and lighter gauge wire; they are not
designed to handle the current draw of the horns. The
illustrations in the 1963 manual are correct.