I would really appreciate that. I’ve been almost to the point of going to my neighbors house (who I’ve never met, but has the same year truck) and asking them if I could look into their engine bay to see where their plug goes haha. Probably not the best way to introduce myself.
And I followed the steps in the trouble shoot guide and it kept leading me to the same question that I couldn’t answer, I think it was #7
Greetings densobro,
I've got a '99 C2500 where the wiring looks to be factory original. I've read your thread with interest,
and I decided to try to help by physically verifying the "Horns Schematics" in the Service Manual with
how my circuit is actually
physically wired. The good news is that my '99 matched the wiring schematic
*exactly*.
Disclaimer: Now given that your '96 (with unknown previous repairs) won't match my '99 exactly, at
least you will be able to see what it looks like when the truck is wired per the schematic.
****
OK, I took
@97Kharon 's schematic & marked it up so that when we look at the actual wiring underneath
the Underhood Fuse Block it will make more sense:
Color coded overlay on factory Horn Schematic
You must be registered for see images attach
Healthy Circuit Behavior:
1) Working backwards from the horn assemblies, +12 volts is sent
only during actual horn operation
on the
green wire between the relay output and the horn connectors. The (verified) physical path
is from the Underhood Fuse Block to
C100, (main connector on firewall to IP
**) then to
C102,
(IP Harness Inline to Forward Lamp Harness) which then runs from beside the engine's black box
all the way over to the horns in front of the single battery on the passenger side. NOTE: In a subsequent
post I'll share the physical path photos for this green wire so that you can compare what I've got to
what you have.
2) The path between the steering wheel horn switch and the control input to the relay is colored black
to denote a ground circuit, but for troubleshooting purposes I'd like to point out an important fact.
If you look closely at the circuit, as long as there is a charged battery in the truck & the Horn Fuse is
not blown, if you were to take a voltmeter to any part of the wire feeding the horn switch you will see
+12 volts parked on the wire. Of course, there is zero current flow
until the driver smashes the horn
button, applying the ground, current flows, and the relay is energized by this flowing current.
I share the above because you can use this knowledge to your advantage while troubleshooting. As
you follow the wiring from
C100 to the "Convenience Center", you can check pin '
F' at
C(onnector)
210,
and if the +12 volts is there, then on to
C266 (IP Harness Inline to Steering Column Harness) pin
A11.
If the power is now missing, we know where to look. Otherwise, it's up the steering column & to the
horn switch & the associated ground.
NOTE: Most people prefer to check for voltage, while the old, grizzled shade tree mechanics would apply
a ground to the points listed in the previous paragraph. Ground to pin F = horn blow! Ground to pin A11 = horn blow!
Now they would have it narrowed down to either an open in the steering column or the horn switch/ground itself.
CAUTION: Using a voltmeter is being a
lot more cautious than applying a ground while troubleshooting.
Why? Because if you NEVER make a mistake, applying a ground is a valid troubleshooting method on this
side side of the horn circuit. On the other hand, what IF you miscount & apply ground to the
wrong pin
in the connector? Best case, you will have to find the fuse on some unknown circuit that you just blew.
Worst case, you may very well just smoked something unrelated yet spendy!
Conversely, voltmeters make their measurement with very low amounts of current, and therefore are
very gentle
(think butterfly wings) on auto circuits = very forgiving not
if, but
when you hit the wrong pin. :0)
****
Apologies for dragging you through the circuit, but now I can better show you what I found on the underside
of the Underhood Fuse Block on my truck:
Check this out - Orange, Green, & Black wires just like the "Horns Schematics" promised!
You must be registered for see images attach
NOTE: A better description for the black wire might be: "Ground from steering wheel horn
switch" (current to ground energizing relay when switch depressed/closed.)
One last thing. I did the 'trust but verify' thing by first removing the Horn Relay & verifying that the horn no workie. Reinstalled relay &
removed the
20A horn fuse -- also no workie! Given this, I now have 100% confidence in both what the schematic and the photo above is showing.
****
OK, for those reading along but you haven't needed to find the horn fuse and/or relay, I've attached a couple of photos to give all this
a proper context. The Underhood Fuse Block is in the right rear corner of the engine bay closest to the driver as seen from the front. (See attached.)
In my next post I'll document the physical path that the green horn wire takes from relay to the horn assemblies for your viewing pleasure.
**IP = Instrument Panel
