1970 (and 69) Heater Box Wiring Variations

[Midlife 814]

While refurbishing 69 and 70 wiring harnesses, I've seen at least four variants of 1970 heater box wiring. All four variants are all electrically equivalent, but have different connectors (some with extensions) and locations for where these wires break out of the main harness. I am at a loss to understand why these versions are so different, but that may be because I am unfamiliar with the 70 heater boxes, of which there may be variations in design and/or location. While the advantage I have is seeing well over 200 harnesses, the drawback is that I don't know the factories or VIN numbers associated with them. Very few harnesses have stickers still attached to help decipher if there was a sequence in time of designs.

 

The first style is what I call "standard", and covers roughly 75% of all 70's and 95+% of all 69's. This style has the three prong spade connector (red, blue, black/yellow) that plugs into the heater box breaking out of the harness near the passenger side door jamb switch.

"Standard" style:

 

What I call Style A has the break-out on the portion of the harness going towards the firewall plug, and the plug is a three-prong flat bullet plug. I believe there is an extension that converts this bullet plug to the standard spade connector in "standard".

Style A:

 

What I call Style B has the same position for the wire breakout of the main harness, but has a longer length and ends up in the "standard" spade plug.

Style B:

I have one picture of this style used in 1969. Almost all 1969's have the "standard" style, which may suggest late 69 and early 70's may have started as Style B.

1969 Style B:

Style C is the rarer of all, and is a combination of "standard" and Style A in that there are two heater box connectors: one breaking out near the passenger side door jamb and the second on the firewall portion of the harness. The heater switch connector itself has doubled up wires.

Style C pictures:

 

 

 

Here's what I can tell so far about these variants. "Standard" style has stickers that show the parts end in at least -B9 and -CH; Style A has a B0, and the 1969 Style B has a -BC suffix. I can't correlate the four variants to the presence of AC, tachometer, or Mach1 configuration. With AC, tach, and Mach1 configurations, there are at least 8 basic configurations for 1970 harnesses (standard or tach dash, with or without A/C, Mach1 or not).

 

What can y'all tell me about 1970 heater boxes? Were they different throughout the year? Different locations?

[miketyler 15]

My Mcode 70 Mach had the C variant with dual fan plugs. My car is a real Mach with 351c, FMX, AC, standard gauge cluster, PS, PB and distributor modulation. On the AC box, the blower fan is located center of the dash and the plug is close to the firewall. The heater-only box must have had the blower very close to the middle of the glove box as thats where the extra plug was located. I have a post or two on this around here somewhere.

 

BTW, the harness you reconditioned works great with no magic smoke released. The tach conversion works fine even with the purple resistance wire removed and he 1/2watt resistor added for the 3G alternator. I get oil and ALT light at key on. The only odd thing is the ALT light stays lit after engine is started but is very dim. The 3G does great and puts out about 14.5v at idle. Am not too worried about the ALT light.

[buening 63]

Mid, have you noticed a variance in the color of the plastic instrument cluster connector on those particular harnesses? I could be wrong, but I think the Mustang used a black connector whereas a Cougar often had either a white or a brown connector.

 

Style C in my opinion is for an A/C car.

[Midlife 814]

Mid, have you noticed a variance in the color of the plastic instrument cluster connector on those particular harnesses? I could be wrong, but I think the Mustang used a black connector whereas a Cougar often had either a white or a brown connector.

 

Style C in my opinion is for an A/C car.

I've not seen a white dash cluster connector, but I see both black and brown all the time (about even distribution) from 69-73. I suspect there were two separate suppliers of that connector (and it is not reproduced separately today nor are the contact pins).

[danno 128]

They had a standard heater box, they had the one with AC, and they also had a "Power Ventilation" option. I thought it would have used the same wires as the standard heater box, but maybe not?

 

My notes are for a 69, because that is what I have. In that year they had 5 different part numbers. C9ZZ-14401 is the basic, and a -B is with a tach, -AC was for a 6 cylinder, -AF is a V8, -AJ is for a V8 Deluxe and AC, and a -BK was tach and AC.

 

The style C is definately from a AC car, because of the little green wire on the fan switch. The green wire goes to the AC mode switch. The AC mode switch is on only when the heater control lever is in the AC mode. It then goes to the thermostat and on to the compressor clutch. But why is there 2 connectors to the resistor/fan??? Maybe this is for the power vent option? Maybe it had an extra fan in it?

[Midlife 814]

They had a standard heater box, they had the one with AC, and they also had a "Power Ventilation" option. I thought it would have used the same wires as the standard heater box, but maybe not?

 

My notes are for a 69, because that is what I have. In that year they had 5 different part numbers. C9ZZ-14401 is the basic, and a -B is with a tach, -AC was for a 6 cylinder, -AF is a V8, -AJ is for a V8 Deluxe and AC, and a -BK was tach and AC.

 

The style C is definately from a AC car, because of the little green wire on the fan switch. The green wire goes to the AC mode switch. The AC mode switch is on only when the heater control lever is in the AC mode. It then goes to the thermostat and on to the compressor clutch. But why is there 2 connectors to the resistor/fan??? Maybe this is for the power vent option? Maybe it had an extra fan in it?

I've seen all three styles with and without AC for the 70's. 2 connectors to the resistor fan? Look again: there are three of them: blue, red, black/green.

 

As far as I know, there's no difference between 69 underdash I6 and V8 harnesses. The 1969 model is the most consistent within model years of all of the vintage Mustangs, with only variations for AC and tach.

Edited August 17, 2013 by Midlife

[danno 128]

Yes, I cannot imagine why they needed a different harness for a 6 cylinder car. That is the notes I had on it, and they could be wrong.

 

Maybe someone with a master parts catelog could solve the mystery. 1970 was when they started doing funky things for air pollution, but that should have only been under the hood.

[buening 63]

Lots of pics of a powervent here: http://www2.cougarpartscatalog.com/p-vent.html

 

Nothing really jumped out at me regarding extra wiring, as it is mostly vacuum controlled like the A/C cars.

 

Below is how my car is set up in regards to the A/C and heater blower. You have the extension harness and that is it for the blower. The extension harness plugs into the dash harness. My car is an early 70 Metuchen

 

 

 

I also found this Ford diagram online and noticed the three prong plug coming off the heater blower switch labeled as "Not Used"