Horn relay modification for 68-69 harness in a 70 charger.

[1970gator]

On my '70 I switched out the engine harness because it needed it.  I had a '68/'69 engine harness new in the box.  So, I am using it.  The 2 changes of note seem to be the electronic voltage reg on the '70s.  The plug was available at O'reillys and the conversion simple on the voltage regulator, but what about the conversion on the harness for the horns.  What will I need to do on the harness to delete the horn relay considering it is located under the dash?

[gtx6970]

You will need a wiring diagram for them both and modify as needed.

keep in mind the alternator wiring is different for 68-69 versus 70

[Nacho-RT74]

The first I would do is get the correct harness and sell the one you have. If is new, I bet you will sell easilly and that will get you the money for the correct one without headache or work on it

But if you STILL wants to convert it, you won't have to worry about the horn wiring. From iniside any year just carry on one wire for the horns, just that 68/69 carries negative source from horn switch to trigger the relay on engine bay, and 70 gets the wire already energized with positive from the relay inside to feed the horns. So, is just about the kind of signal carrying on and the wire color: earlier got black which is the color coming out from stering column on all years, 70 got green traced green which is the relay output color on all years. You'll need to be sure just the harness plug terminal location meets the cavity on your bulkhead for the horn ( which it should )

Then the 68/69 got an extra pigtail ( Violet wire )  from alt post to feed the horn relay... you simply won't use it.

About elect voltage regulator. It seems you are already set on what you need to do.

Another difference is on 68/69 the wire to coil is blue, while on 70 become brown. This is because the run circuit which is blue in all years, now need to reach the alternator fields, so to don't run two same blue wires up to front of the engine, the coil wire become on the same ign2 color, feeding the ballast, so now is brown. Then you'll find a blue wire on lates harnesses not to feed the coil, but the alt field.

Another diff ( on the kind of signal ) is on all regulators system the green wire is the regulated source, BUT, on mech regs the regulated field is positive and the constant source field is grounded to chassis to be feeded negative, while on elect regs the reg field is now negative and the new blue wire from RUN circuit up to alt field is the one getting constant positive, ( hence why both brushes are wired and isolated from alt housing )

This is what sets all differences on 68/69 againts 70.

I hope is clear

[Staxbro]

Hey Nacho. I have a question linked to this.
My 68 had the horns mounted in the wrong place (under battery tray) no relay at all and a hot feed from the fuse box, to a button on the dash through the firewall and a massive cable running to the horns. I have just finished rewiring the dash and want to reinstate the original relay. It just arrived today ( I am in UK 🇬🇧) and was wondering about the routing of the violet wire with the main supply. I assume it comes from the alt post and runs with the forward lighting harness all the way to the end at the front RH headlight and then into the radiator mounting panel? I am also assuming that the horn ground wire runs with the temp sensor along the valve cover and then over with the washer pump wire and the to the relay?

Trying really hard to put the car back to factory spec with sensible uprating in a few places. Thanks.

[Nacho-RT74]

The horn violet wire up to 69s is just a splice from the alt stud eyelet terminal straight to the horn relay, allong with the horn switch wire from stering column... both wires are part of engine harness and reachs directly from alt the horns relay attached in radiator core support on right hand, just like you mentioned, the valve temp sender wire and windshield washer wire ( and coil wire if big block ), all allong the valve cover

[Nacho-RT74]

@1970gator i think you could get here a harness buyer and get the propper one for your 70 LOL, depending on what engine have both and charging and ign systems.