Help identifying dash wiring harness plugs

Please help identify these connections. This is every plug I could find under my dash. I will update my OP with answers as others may find this a useful reference. If this already exists, I'd love to see it. It was suggested that this is a 72 harness with automatic transmission and A/C but the car is originally a 71 with manual and A/C. If you know the designation of the plug, that's even better (like c-21 or whatever it shows on the diagram).

I am also looking to figure out how to confirm if my car originally came with a tach and if this harness is for a tach

1: Rear Lighting (please let me know if you know specifically)
2: Rear Lighting
3: Trunk courtesy lighting
4: ?? (located at main wiring harness firewall pass through)
5: C-136 Headlight/Dimmer Switch
6: Optional under dash courtesy light
7: Windshield Wipers
8: Cigarette Lighter
9: C-21 (Emissions-goes to engine bay on firewall)
10: C-28 Ignition Switch
11: Turn Signals/Horn
12: 4 way flashers
13: Radio
14: Clock
15: Blower Motor
16: ? (Maybe a light)
17: [heater/AC extension plug to mate switch to blower motor]
18: Cut wires to 17
19: Center console gauges (c-114???)
20: power and output from circuit breaker to 4 way flasher
21: Turn Signal Flasher
22: optional parking brake and headlight on for convenience panel
23: RH underdash optional courtesy light
24: Seat Belt Light

351mach1 said:

Please help identify these connections. This is every plug I could find under my dash. I will update my OP with answers as other may find this a useful reference. If this already exists, I'd love to see it. This is a 72 harness with automatic transmission and A/C. If you know the designation of the plug, that's even better (like c-21 or whatever it shows on the diagram)

1: Rear Lighting (please let me know if you know specifically)
2: Rear Lighting (please let me know if you know specifically)
3: ?
4: At main wiring harness firewall pass through
5: C-136 Headlight/Dimmer Switch
6: ?
7: Windshield Wipers
8: Cigarette Lighter
9: C-21 (Emissions-goes to engine bay on firewall)
10: C-28 Ignition Switch
11: Turn Signals/Horn
12: ?
13: ?
14: ?
15: Blower Motor
16: ?
17: ?
18: ?
19: Center console gauges (c-114???)
20: ?
21: Turn Signal Flasher
22: ?
23: ?
24: Seat Belt Light
View attachment 95458View attachment 95459View attachment 95460View attachment 95461View attachment 95462View attachment 95463View attachment 95464View attachment 95465View attachment 95466View attachment 95467View attachment 95468View attachment 95469

Click to expand...

This is for an early 1971. How do I know? Your plugs 1 and 2 were changed early on.
3. for rear trunk courtesy light option
6.for optional underdash courtesy lights
12 4 way emergency flasher plug
13. radio power and lights
14. clock plug
16. For light on console?
17. This is what I call the heater/AC extension plug to mate switch to blower motor
18. Cut wires to 17.
20. power and output from circuit breaker to 4 way flasher
22. optional parking brake and headlight on for convenience panel
23. RH underdash optional courtesy light

Does the Marti Report tell if mine originally came with Tach? How can I verify if the harness in the vehicle is supposed to be for a tach cluster? It currently has an inoperable clock cluster in it but it wasn't even hooked up at all. It has the three gauges in center console

Here's what's confusing: The car is a 71 m code with 4 speed and A/C from California. It was converted to a later (73-74) engine and auto tranny. I have a hunch that there was a 72-73 donor car involved as a bunch of the dash is from a 72 [to my understanding] as it has the seat belt light above the glove box. I am trying to not make assumptions about anything that's in there. It has all the appropriate plugs for the auto transmission (and maybe an extra?). I think it would have been easier for them to just swap a full wiring harness from a donor than to disassemble two complete wiring harness' just to add the auto trans plugs.

Yep. The instrumentation group included the tach and the oil, amp, and temp gauges.

Sheriff41 said:

Yep. The instrumentation group included the tach and the oil, amp, and temp gauges.

Click to expand...

This is one of Ford's "non-Better Ideas". The Mach 1 Sports Interior included the triple gauge cluster and a clock in the LH dash pod. You had to also buy the Instrumentation Group in order to get the tachometer and trip odometer.

351mach1 said:

Does the Marti Report tell if mine originally came with Tach? How can I verify if the harness in the vehicle is supposed to be for a tach cluster? It currently has an inoperable clock cluster in it but it wasn't even hooked up at all. It has the three gauges in center console

Here's what's confusing: The car is a 71 m code with 4 speed and A/C from California. It was converted to a later (73-74) engine and auto tranny. I have a hunch that there was a 72-73 donor car involved as a bunch of the dash is from a 72 [to my understanding] as it has the seat belt light above the glove box. I am trying to not make assumptions about anything that's in there. It has all the appropriate plugs for the auto transmission (and maybe an extra?). I think it would have been easier for them to just swap a full wiring harness from a donor than to disassemble two complete wiring harness' just to add the auto trans plugs.

Click to expand...

The factory tach will plug into the dash harness behind that clock pod. It'll have a two position rubber plug with one male and one female connector.

The main harnesses are universal with regards to transmission type. The neutral safety switch can be unplugged and the reverse light switch harness / starter circuit jumper can be plugged in.

FWIW, with that much non-71 parts, I'd start looking for the partial VIN stamps on the outer edges of the shock towers.

Hemikiller said:

The Mach 1 Sports Interior included the triple gauge cluster and a clock in the LH dash pod. You had to also buy the Instrumentation Group in order to get the tachometer and trip odometer.

Click to expand...

Just to confirm, according to the Marti report, my vehicle should have came from the factory with a tach since I have the "instrumentation group". So I should be able to find a tach plug back there.

You are also saying that all the harnesses were generic with the auto transmission plugs already installed, just not used of it was a manual?

Lastly, I did have a heart attack the other day and pulled off the fender to check....

Hemikiller said:

The factory tach will plug into the dash harness behind that clock pod. It'll have a two position rubber plug with one male and one female connector.

Click to expand...

Does anyone have pictures of said plug and cluster? I am not finding it on my harness. Could it be number 16 in my photos above?

351mach1 said:

Does anyone have pictures of said plug and cluster? I am not finding it on my harness. Could it be number 16 in my photos above?

Click to expand...

I don't believe 16 is the tach connector. Mine is a different year, so I'm not 100%. I have the same red 2-pin connector from down by the heater controls. I'm using it to pull power for the lights. I believe that one is either meant to be for the lightbulb in the heater controls or a feed to the console lighting. I believe the corresponding red 2-pin connector is on the back of the HVAC control unit. The 2 red plugs connect.


The tach connector is a physically a couple feet away from the AC controls. I can't get a good picture of mine. It is that same shape as 16, but black. The wire is coming from over top of the steering column.

My guess for #4, if we're still guessing, is the parking brake.




On your picture of #17, that looks like the heater box in the background and possibly an orange wire running up over the transmission hump at the very top of the photo hiding in the back. The cut wires from #18 go back in there and plug into a 3-prong connector on the heater box. Maybe check if that orange wire is part of those 3 that are cut.

351mach1 said:

Please help identify these connections. This is every plug I could find under my dash. I will update my OP with answers as others may find this a useful reference. If this already exists, I'd love to see it. It was suggested that this is a 72 harness with automatic transmission and A/C but the car is originally a 71 with manual and A/C. If you know the designation of the plug, that's even better (like c-21 or whatever it shows on the diagram).

I am also looking to figure out how to confirm if my car originally came with a tach and if this harness is for a tach

1: Rear Lighting (please let me know if you know specifically)
2: Rear Lighting
3: Trunk courtesy lighting
4: ?? (located at main wiring harness firewall pass through)
5: C-136 Headlight/Dimmer Switch
6: Optional under dash courtesy light
7: Windshield Wipers
8: Cigarette Lighter
9: C-21 (Emissions-goes to engine bay on firewall)
10: C-28 Ignition Switch
11: Turn Signals/Horn
12: 4 way flashers
13: Radio
14: Clock
15: Blower Motor
16: ? (Maybe a light)
17: [heater/AC extension plug to mate switch to blower motor]
18: Cut wires to 17
19: Center console gauges (c-114???)
20: power and output from circuit breaker to 4 way flasher
21: Turn Signal Flasher
22: optional parking brake and headlight on for convenience panel
23: RH underdash optional courtesy light
24: Seat Belt Light
View attachment 95458View attachment 95459View attachment 95460View attachment 95461View attachment 95462View attachment 95463View attachment 95464View attachment 95465View attachment 95466View attachment 95467View attachment 95468View attachment 95469

Click to expand...

Thanks, you just saved me hours of work!

16 is definitely for the heater control. I just plugged it back in.

I would say you are correct for 4 as well. My parking brake sensor is missing which is why I couldn't figure it out.

So the current cluster I have is miffed. I see I can buy a new printer circuit board for it. Id love to have the original tach cluster in there.
A: how hard and expensive is it to find a tach cluster?
B: if I replace the circuit board on this current cluster, in theory should all my gauges start working?
C: I see rocketman does a tach conversion. I have more questions :|

Attached picture is the only unaccounted for wire anywhere close to the tach but it is not as described above

351mach1 said:

Does anyone have pictures of said plug and cluster? I am not finding it on my harness. Could it be number 16 in my photos above?

Click to expand...

Here's one from an eBay listing, don't underestimate it as a research tool. Red w/Light Green stripe wires, two place rubber plug, one male, one female.

351mach1 said:

Just to confirm, according to the Marti report, my vehicle should have came from the factory with a tach since I have the "instrumentation group". So I should be able to find a tach plug back there.

You are also saying that all the harnesses were generic with the auto transmission plugs already installed, just not used of it was a manual?

Lastly, I did have a heart attack the other day and pulled off the fender to check....

Click to expand...

Yes, since the Instrumentation Group is listed on your Marti Report, it was equipped with a tach. Now, whether the harness that's currently installed has a tach plug is another matter entirely.

Yes, there is no difference in a dash or headlight harness for a car with an auto or manual transmission.

From your pic below - Blue - seat belt warning system (shouldn't be present in a '71), White - auto shifter illumination, not used on manuals. Black - NSS connection, manuals have a sub-harness that plugs into this connector, with a jumper for the starter circuit and a connection to the reverse light switch on the shifter body. NPD has reproductions of that harness. You can see the harness on my toploader below.





FWIW, much of the information you're looking for is literally in the palm of your hand. The color codes on the wires will guide you to the answers. There's two methods I use, one is to simply look at the color listings on the pages of the wiring diagrams, the other is to cross reference them to the PDF I've attached. Ford used specific color wiring for specific purposes, and there is very little cross-pollination or overlap. IE: Red w/Yellow hash marks is always the emissions circuit, it powers the anti dieseling solenoid and the distributor modulator system (which you car was likely equipped with. Pay attention to the circuit numbers as well, those will also help.

The plug to the tachometer will have a re with light green stripe wire on both sides of the plug.
You might want to download the wiring diagrams from our Wiki, it will make it easy to determine what plugs are for, based on wire color codes:
https://cdn.imagearchive.com/7173mustangs/images/1971_full.pdf
You can also get colorized wiring diagrams with the shop manuals from Forel Publishing or from Mustang parts vendors.
The Electrical Assembly Manual, part of the Assembly Manuals, also has a lot of useful information.

Thank you everyone for your help and enduring my questions and pointing me where to find more information.

I think we can conclude that this is not the original harness as it does not have the input for the Tach but also the dash cluster is the 18 pin variety instead of the 12 pin.

Following up, in your opinion, [given that I have a 72 harness w/out tach) what is the easiest way to get my dash back to original operation i.e. Tachometer and center gauges working correctly.
-My thought is the cheapest way is to add an aftermarket tach.
-Is it possible to get the center gauges to operate while using the clock version of the instrument cluster?

Final question, why does the 18 pin connector and instrument cluster pins not line up? More mish mash of parts?

It would appear that your harness does have the 5v wire coming off the back of the instrument connector. That feeds the center gauges. And you have that 8 pin connector in your photo #19. Those, and the sending units, should be enough for the center gauges to work if you had a set of them.

And if you don't have the hookup for the factory tach, then I think the rocketman conversion would be the easiest to wire up. Just hot, ground, and connect a wire to your coil.

For your question about mismatched cluster and wiring harness, maybe the mismatch is because the wiring harness is not from a car with the same options. Like not all cars had the dummy lights in the dash.

First off, in 1971, you could get a standard dash cluster (clock, speedometer) with the 3 gauge cluster as an option. For 1972 and 73, you could only get the 3 gauge cluster WITH the tach dash cluster.
Several things bother me about your harness. The seat belt interface in the engine bay (blue square plug) wasn't used early in 1971, and the 4 pin engine gauge feed harness started in 1972. With confirmation of the early 71 harness (tail-light connectors indicate that....), I believe your main engine bay harness is a 72. It's reasonably compatible with the 71, but not with AC hookups. I'll bet you'll find a pink molex connector near the fuse box/headlight junction box that's attached to the engine bay harness. If so, that would confirm the 72 engine bay harness.

Alternatively, someone may have swapped your underdash with a 72, made changes to have it interface with the 3 gauge cluster and the tail-lights.

midlife said:

I'll bet you'll find a pink molex connector near the fuse box/headlight junction box that's attached to the engine bay harness.

Click to expand...

Is my number 9 in the photos above what you are referring to?

351mach1 said:

Is my number 9 in the photos above what you are referring to?

Click to expand...

Yes it is! You definitely have a 72 headlight harness. Do you have sportslamps? Just curious...

@midlife Yes, I have the sportslamp

I replaced the circuit board on my cluster and plugged it in as it is currently wired and everything seems to work correctly including the gauges. Unfortunately the gauges work intermittently and I cant figure out where the loose connection might be. It doesn't seem to be triggered by bumps in the road. Just randomly as far as I can tell for now.

I then installed new instrument illumination bulbs for the light switch, wiper switch, and cig lighter. The light switch bulb wont illuminate and I am reading ~2 volts at the socket. Also, there was some loose connection associated with the cigarette lighter causing all the accessory illumination bulbs to flicker. I removed the cigarette lighter wires and that seemed to solve flickering lights but now when I turn on the headlights, I can hear strain on the engine and an alternator belt chirp which I never noticed before. It could have been like that before but I just now noticed it. Also, now the instrument gauges stop working as soon as I turn the headlights on. Once I turn the headlights off, the gauges work again. Prior to this point the gauges were intermittent randomly. Anyone seeing a pattern here to look into?