Mark Houlahan
Tech Editor, Mustang Monthly
April 23, 2019
Photos By: Courtesy of National Parts Depot

One of the Mustang’s first print advertisements touted, “Mustang is designed to be designed by you.” In essence, Ford was promoting the many options the Mustang had available to personalize the car for each customer—from factory-installed options like engine, transmission, and interior features to dealer-installed options that ran the gamut from convenience items to performance bits. You could literally build a low-budget inline-six commuter, a high-performance tire-chirping ride, or load your Mustang up with luxury options to make it the ultimate cruiser. The choice was yours.

Early on in the Mustang restoration hobby, it was tough to add options that weren’t originally found on the car you were working on. If you wanted a V-8 engine with five-lug power drum brakes and Styled Steel wheels, you generally had to find a wrecked “donor” Mustang and transfer all the parts to your restoration project. This held true especially for “soft trim” parts like interiors. Many ’65-’66 Mustang owners have coveted the Interior Decor Group option, popularly called the Pony interior due to the running horses found in the seatback inserts. However, even though the upholstery was reproduced early on, the many other facets of the Interior Decor Group would take many years to come to your favorite Mustang parts catalog.

As the saying goes, where there’s a will there’s a way, and many owners have cobbled together the Interior Decor Group for their Mustang through a combination of reproduction, original, and owner-made pieces over the years. Our own ’66 Mustang project, which graced the pages of Mustang Monthly from 1999-2001, was the recipient of an Interior Decor Group upgrade. We remember having to make our own seat listing wires (now reproduced) and sourcing a used deluxe steering wheel from the swap meet at a Carlisle Ford Nationals show to be restored by Orlando Mustang. Today you can find everything reproduced, except for the five-dial instrument cluster back plate. You’ll also have to find original deluxe seatbelts and have them restored by a company like Ssnake-Oyl Products (ssnake-oyl.com). Is the conversion cheap? Certainly not, but if your Mustang restoration requires a full interior replacement/restoration, the cost is not that much more to go “Pony” over the base interior, considering you need seat foam, upholstery, and more anyway.

This isn’t a traditional “how-to” story. It’s more of an Interior Decor Group spotter’s and parts guide so you’ll know what the differences are between a standard and Interior Decor Group interior. We’ve also gathered up all the parts needed for a complete conversion, with part numbers, courtesy of the National Parts Depot catalog.

Parts Required for Pony Interior Conversion 
ItemNPD PN
Seat upholsteryUD-X-X-X (PN determined by color/body style)
Front seat bunsDF-56
Listing rods65446-1B
Kick-panel chrome02345-6-1A
Kick-panel carpetKPC-X-X (PN determined by color)
Woodgrain instrument bezel10838-2A
Woodgrain glovebox door06024-4
Quarter-trim upholsteryQT-X-X (PN determined by color)
Quarter-trim padding31488-1B
Quarter-trim corner caps31491-1A
Door panelsPD-X-X (PN determined by color)
Door-panel trim20942-3-1A
Door-panel mounting kit23943-2AK
Hand-cup mounting brackets (x2)240A10-1A
Door-panel cups (x2)PC-X-X (PN determined by color)
Door-panel-cup inserts (x2)PI-X-X (PN determined by color)
T-bird-type door handles22600-2A and 22601-2A
Door-handle escutcheons22620-1A
Door-handle shaft assembly21818-2A and 21819-2B
Door courtesy lamps (x2)13786-1A
Wire looms for door lights (x2)13A769-1A (W/O speakers) 13A769-1B (W/ speakers)
Master interior screw kit03000-2BK (HT), 03000-1BK (FB), 030003BK (CV)
Deluxe steering wheel3600-5A (3600-5AK or 3600-5CK for complete kit)
Steering wheel center cap3623-1B
Steering wheel lower trim3491-1A or 3491-1B
Steering wheel horn ring13A805-2A
Steering wheel springs/insulators13A891-2K
Steering wheel horn contact plates13A808-2B
Stainless steel-trimmed gas pedal9735-1A
Stainless steel brake-pedal trim2A487-1A (auto), 2A487-2 (manual)
Stainless steel clutch-pedal trim7B544-1

Additional 1965 Model Conversion Parts 
ItemNPD PN
1966 glovebox latch06072-02
Underdash harness14401-1C
Headlight harness14290-1C
Oil sending unit9278-2
Oil sending unit extension9B339-1
Alternator wiring harness14305-1E (I-6), 14305-1EA (V-8)
Engine-gauge wiring harness14289-XX (PN depends upon engine and heater speeds)
Used five-dial gauge clusterSource locally or through classified/online ads

Starting with a standard interior shown here, the seats feature horizontal ribs with a “wrap-around” vinyl facing. The door panels are simple flat fiberboard with a bolt-on armrest, and the metal rear quarter trim panel is simply painted to match the interior door shell.
The Interior Decor Group (which we’ll simply refer to by its popular slang term—Pony interior) raises the bar significantly just about anywhere you can look or touch in the ’65-’66 Mustang’s interior. Starting with the revised seat foam and upholstery, sculpted door panels with integral armrests, padded vinyl-covered quarter trim panels, carpeted kick panels with bright trim, a woodgrain-look steering wheel, and woodgrain appliques on the gauge cluster, glovebox, and console (if optioned).
While the seat frames are identical, to upgrade to the Pony interior seats requires new seat foam on the front buckets. This foam has revised bolstering and the proper slots/positioning for the revised Pony upholstery’s listing wire locations.
Speaking of listing wires, those too are different between the standard upholstery and the Pony option. Reproduction listing wires are available now, which saves a lot of time/hassle making your own.
Of course, what everyone sees is the upholstery with that beautiful running Pony insert panel on the front and rear seats (except for fastbacks; they don’t have the insert on the rear seat). Once you have the updated Pony-specific seat foam and listing wires, the upholstery installation is no different than replacing the base setup. While black is the most common conversion, you can find all of the original OE color combinations, including two-tone setups in the Pony upholstery. TMI Products (tmiproducts.com) even offers a Sport seat setup with higher bolstered foam and matching Pony upholstery if you want a little more support in an OE-looking seat.
Sadly the bench seat option found in the early Mustang was not available with the Pony interior; however, we’ve seen people have custom upholstery made up with the running horse insert added for a custom Pony interior bench seat setup.
The Pony interior door panels are a direct swap for the stock door panels, but the panels require additional parts, including the two-piece stainless trim and the door panel pull cup with rubber insert.
Before installing the door panels, you’ll have to update the door shell with this door cup retaining bracket and the long shaft door latch. These are both direct-fit items that require nothing more than a screwdriver to install. The bracket supports the door panel pull cup/armrest area and the longer latch is required due to the thickness of the Pony door panel.
A little-known difference in the Pony door panel installation is that it requires different door panel clips, so make sure you order this great kit which includes the correct-length clips with their foam insulators, mounting screws for the door cup bracket, and screws for the stainless trim.
The final piece of the Pony interior door puzzle is the courtesy light. Some people skip these because you do have to cut a hole in your lower door shell, but to perform a complete conversion you must do the lights. The hole isn’t that hard to do, and the wiring harness for the light plugs right into the doorjamb switches. Note that there are harnesses for with and without door speakers, so if you’re considering door speakers as well (not part of the Pony interior, but a popular upgrade), make sure you order the correct harness.
The Pony interior’s woodgrain bits are typical of ’60s and ’70s cars; adding woodgrain trim screamed “luxury.” For the Pony interior package, Ford added the woodgrain trim look to the gauge cluster, glovebox, and the doors with the use of Thunderbird-sourced “pistol grip” door handles. If the car was ordered with a factory console, the console top would receive the woodgrain treatment as well. If converting a ’65 Mustang, you’ll need to add a ’66 glovebox latch to your list along with a used five-dial gauge cluster to refurbish. Don’t forget the Pony door panel–specific chrome escutcheon that mounts behind the door handle too!
Speaking of woodgrain, one of the central Pony interior pieces that is also given the woodgrain treatment is the steering wheel. Available as a separate option, the woodgrain steering wheel is a must if you wish to do a proper Pony conversion. In the past, your best option was to restore a used wheel with a real walnut wood grip. However, you can now source an excellent reproduction of the woodgrain wheel. You’ll have to piece the assembly together by purchasing the horn ring, center cap, rear bezel, and all the screws/spacers/insulators to make the horn ring work. It can be one of the more expensive parts of the conversion, but you can do the wheel at any time for that matter if you’re looking to convert your interior in stages.
Pony interior cars carried the door panel trim forward into the kick panel using add-on trim and carpet to the stock kick panels. You can use your existing panels; simply order the lower carpet section to match your carpet color and glue it down, topping it off with the new trim.
On hardtop body styles with the Pony interior, Ford didn’t forget about the back seat passengers either. Besides adding matching rear seat upholstery, Ford added a padded vinyl cover to the standard pebble grain metal quarter trim interior panels and capped off the forward corner with a stainless trim piece where the windlace begins. You can easily add the look with pre-cut/sewn vinyl trim, pre-cut padding kits, and the stainless caps.
Even the gas, brake, and clutch (if equipped) pedals get the premium touch, with bright stainless trim surrounding the pedal pads. The gas pedal is a complete assembly, but the brake/clutch trims are simple upgrades you add to your existing pedal pads.
While you can reuse some interior fasteners or buy in smaller kits, we highly recommend these master interior fastener kits from AMK that NPD carries. Everything is brand new, the correct length and finish, and individually packaged and labeled to make your Pony interior upgrade go smoothly!
Here’s something that many don’t think about when converting a ’65 Mustang over to Pony interior. Since you’re losing the “Falcon” cluster when you upgrade to the five-dial cluster used in the ’65 GT and in all ’66 Mustangs, you’re upgrading from an oil light to an actual gauge. This means you need to change the sending unit from the small “idiot light” style to the large diaphragm model, and to do this you need this oil pressure sending unit extension to space the larger sending unit away from the block.
Specific to converting a ’65 Mustang with the Falcon-style cluster is the need to update pretty much all of the wiring from the dash forward. This includes the underdash and alternator feed harnesses (shown here), but it also includes the headlight harness and engine gauge feed harness. These harness updates are required for the specific wiring needs of the five-dial instrument cluster. If you have a ’65 GT, you’re all set since you have the five-dial cluster already.

Photography by Mark Houlahan & Courtesy of National Parts Depot