1974 Charger SE tachometer wire harness puzzle.

[74ChargerSE440]

The manuals and wiring diagrams seem somewhat contradictional and my wiring is a bit messy unfortunately. Confusing to say the least. So let's ask this forum (again). I could not find a definitive answer yet.
- How does the wiring go through the firewall? Slot 4 in the bulkhead or via grommet in firewall?
- Which color does this wire have?
- Is the wiring from tachometer to firewall part of the main harness or is it a separate wire?
- Did the wire harness set up undergo a midyear change as some ebay seller suggests? I have a 1973 build, more precisely the 8th of November.

Pictures always help!

Thanks.

 

[Gold Rush]

Per my FSM the tach signal comes from the coil negative terminal on wire # T11 18GY* to bulkhead connector CE2 pin 4. From there on to the tach as wire # T11 20GY*. The other tach wire is T13 20 DBL to CI 40

Hope that helps. Can't tell from what I see but expect that wire would be part of wire bundle for protection.

 

[Nacho-RT74]

on 71 and 74 the tach/coil wire runs throught the bulkhead at the NSS harness plug. on 74 at the only cavity free by the NSS harness. 72 and 73 throught the firewall with a grommet.

The power comes from a yellow rubber mold power feed (tan wire), 3 bullet terminals provision coming out from underdash harness, hanging out from the tape close to the brake pedal area

 

[74ChargerSE440]

on 71 and 74 the tach/coil wire runs throught the bulkhead at the NSS harness plug. on 74 at the only cavity free by the NSS harness. 72 and 73 throught the firewall with a grommet.

The power comes from a yellow rubber mold power feed (tan wire), 3 bullet terminals provision coming out from underdash harness, hanging out from the tapeclose to the brake pedal area

Thanks for your reply. What is NSS?

 

[Gold Rush]

Hey Nacho, from time to time I've read you pointing out some features are done such and such a way if the vehicle was built is some country other than the USA. Is this one of those situations? The 1974 FSM I have does not give any other connection possibilities than the one I described. Also is it possible early or later production dates would come into play?

 

[QuickBpBp]

Thanks for your reply. What is NSS?

Nuetral Safety Switch

 

[Nacho-RT74]

Hey Nacho, from time to time I've read you pointing out some features are done such and such a way if the vehicle was built is some country other than the USA. Is this one of those situations? The 1974 FSM I have does not give any other connection possibilities than the one I described. Also is it possible early or later production dates would come into play?

I’ll have to check since I’m speaking from memory, without talking about the code connection’s used on 74 Diagrams (diff from previous years) like you mentioned. But if you say about I could be speaking the Venezuela assembled models, 74s were wired kinda similar to USA 71s, without anything of the interlock system. I’m really talking about the USA versions perspective.

In any case the cavity 4 is located into the NSS harness bulk. And the Tach is normally feeded from accesories feed which is the one I’m describing.

on a side note: I rewired my car just like 74 USA versions, adding every feature they came out from factory up there, including the interlock system.

 

[Nacho-RT74]

while I don't have my 74 FSM to check for the conection code ( it's 6500 miles from me, along with my Charger ) this is what the 73 diagram shows I have and is pretty much the same for all 71/74 for all the 71/74 accesories.

This is the mold to search for ( circled 1 )

 

[Nacho-RT74]

I do have the 74 master diagram on my laptop, not the legend thought, and it shows, as you stated, the CI40 conector. WHICH if you search on the connections legend on the FSM, SHOULD show the same mold.

Diagram shows same accesories to the same CI40 conector, so even I don't have the legend with me, just the scanned master diagram I post, tracking the wiring on diagram takes to the conclusion, is the same mold shown above with same tan wire to feed that mold

 

[Nacho-RT74]

Now, about where the coil signal to tach leaves the cab ( or enters into the cab ) changes along the years there is a reason why was made on that way.

On 71 the NSS harness got just the reverse light signal into the cab, not the safety ground signal thought, so two cavities were empty on them. These cavities were used to the A/C wires ( blower and compressor, green and blue respectively ), but the engine harness got one cavity left... used for tach if equipped ( I correct myself, was not the NSS plug on 71... memory failed ). Heater cars just the blower wire on this NSS plug.

on 72 and 73, the safety ground signal needed to get into the cab to make work the seatbelt system warning signal ( 71 was a time delay flasher controled just like the ign courtesy light... no buzzer for it thought, just the light ). Hence the NSS harness plug got 3 cavities in use. The empty cavity left was used for blower, since no matter if A/C or Heater the blower was allways present. The empty cavity on engine harness was used on A/C cars for the compressor. The tach was less common than A/C cars, so this wire run throught the firewall with a grommet.

On 74 the NSS harness plug composition was the same than 72/73, getting the safety ground signal to the interlock. BUT the FULL A/C HARNESS ( blower and compressor ) did run throught the firewall with a grommet. Why? the interlock control system needed to run an extra wire on engine harness for the dual starter motor signal, one for the starter motor relay and the other one for the interlock control bypass button. Not anymore cavities left on this harness. With the new A/C harness path throught the firewall and not the bulkhead, the NSS harness plug got a free cavity again, being used for the tach if equipped.

Now I have the doubt about if a Heater car which uses just one wire for the blower, got this wire running thought the firewall or, if being a non tach wire, used the NSS harness plug, like 72/73. Would need to check further for this on diagrams options.

However I can show this bulkhead and firewall disposition for the full option cars on 74. The firewall grommet for A/C shows heater should get its blower wire configured on the same way. I guess to keep the standard configuration no matter the car options