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I’ve got that harness from them, just trying to decide when I can install it, engine in the car but turbos off for the bnr swap as well as the UIM for secondary fuel rail and injector swap. Im debating seeing how difficult it is to do with that much room or there’s connectors I can’t snake through. The harness is exceptionally well made and not the heat soaked OEM one I’ve have since 94.
I’ve got that harness from them, just trying to decide when I can install it, engine in the car but turbos off for the bnr swap as well as the UIM for secondary fuel rail and injector swap. Im debating seeing how difficult it is to do with that much room or there’s connectors I can’t snake through. The harness is exceptionally well made and not the heat soaked OEM one I’ve have since 94.
Thats really cool you have it in hand. I like how they also label the connectors.
I found another harness on E-bay to convert to single turbo, it would be a shame to buy the wiring specialties harness just to cut it up.
I would definitely put a couple wraps of high temp silicon tape over the loom where is crosses over the turbos like the factory harness.
Since Ive done it both ways, (installed the engine/emission harness on the engine in and out of the car). My favorite way is "if the engine is already outside the car", engine transmission bolted together and harness routed between both. turbos off, UIM off, and install into car.
I know more experienced people have a way that works better for them as well, it's really what works best for you.
There are many options for upgrading the ignition of the FD3S from replacing the coils, adding aftermarket spark amplifiers, to getting new engine management. True this has been done in the past by some incredible RX7 tuners, but from what I am aware of there was not a plug and play harness until now. In this update I'm going to share a nice little upgrade that you can do for the ignition that will get you the best bang for the buck. Also the main reason for this upgrade is to give the coils direct battery power so they can charge up faster between firings, thus reaching their full capacitance for the next fire.
Lets first give a shout out to some guys who made this possible.
Xavier for all of his insight in automotive electrical systems and for creating FC Tweak and his products for the FD3S. https://www.facebook.com/FCTweak/
Jim from the RX7 club who built the Ignition Mini and Ignition Complete harnesses so that we could all benefit from this simple affordable upgrade. Jim also has many other harnesses like the plug-n-play fuel pump relay harness for our cars as well.
01. The "new" plug-n-play +12V ignition harness upgrade options
02. Igniter Restoration
03. Ignition Complete-Harness connected
01. The "new" plug-n-play +12V ignition harness upgrade options
The factory coils receive +12v power through the ignition switch, this is also shared with the fuel pump and the cars electrical system. One great upgrade to power the fuel pump is to switch the power source from the ignition to the battery via a relay. This is the same upgrade that has been done for the stock coils but now thanks to Jim we have a true plug and play harnesses.
The stock 12V pathway for the coils: Battery -> X-01 -> X-02 -> IGN/X-03 -> X-11 -> B1-14 -> Coils
Option 1. Mini-Harness 12V pathway: Battery -> Mini-Harness -> B1-14 -> Coils (can use HKS after relay)
Option 1 and 2 are very easy to use since you can leave the factory coil harness in place and just install the mini harness in between the engine harness and coil harness at connector B1-14. However for Option 2, if you have an HKS twin power you must connect it after the Mini-Harness since its performance will be affected by the relay. Option 3 requires the removal of the stock coil harness and you replace it with the Complete-Harness. Since the relay is built into the complete harness you cannot use the HKS twin power, but this option replaces your old wiring and gives the coils battery power without any additional connectors in the way. This is the way I went since I already relocated my stock coils to where the factory cruise control used to sit. OK let's get to the reason why the HKS twin power should not be used before any type of relay.
I wanted to know how the relay would affect the HKS twin power so I contacted Xavier of FC Tweak. The short answer is NO, the HKS twin power must be used after any relay and closest to the coil harness.
Here is the long answer. The Twin Power derives its name (Twin) for its dual function. Function (1): it resonates with each primary coil to convert the single ignition pulse from your igniter into a high frequency alternating current which transforms the ignition spark from a single shot spark to a multi-wave plasma (energy and dwell time remain the same but combustion efficiency and spark duration both increase and are especially beneficial at low RPM). Function (2) is its ability to add capacitance across the ground and main positive coil supply (common for all coils), thus charging up its internal capacitor while the coils are in their off state. When this capacitance is wired as close to the coils as practically possible, the energy stored in this capacitor will result in a higher 'punch' of voltage level during the coil on-time and hence increase the spark energy. If you wire up the Twin Power supply line before any relay, this capacitance effect will be cancelled by the extra inductance and resistance of the longer cable feeding the +ve supply of your coils, and hence kill all the benefits from function (2). Technically speaking, capacitive reactance and inductive reactance have opposite signs. So ideally the Twin Power should be wired up as close as possible to the coils, that's why it comes with an adapter harness which connects straight to the factory coil harness.
So there you go.
02. Igniter Restoration
I never considered the igniter heatsink being an issue. I thought it was a one piece design and didn't use any type of thermal paste. So during my conversations with Xavier, he mentioned to give the igniter a refresh. This is what he said - and boy was he right!!!
Xavier - If you are keeping the factory ignitor, I recommend you unmount the ignitor module from its heatsink (2 phillips screws), clean up all the old baked heatsink compound, sand down both heatsink and module surfaces to shine finish over a flat surface, and spread new CPU heatsink compound. Replace all screws and mounting bolts with new galvanised ones and put everything back together. Fit a new grounding cable from one of mounting bolts to engine block. This should be more than enough for your setup. The relay should also help to reduce the factory cable voltage losses.
I removed the igniter and started taking it apart. There was no thermal paste at all between the igniter and the heatsink. The funny thing is I remember using a cleaner to clean the oxidation on the igniter, I didn't realize it would also remove the paste between the igniter and the heatsink. I sanded down both surfaces and used some artic silver for the thermal paste. I also got all new hardware with toothed washers for a better bite for the electrical bonding. I attached the ground to the screw that holds the igniter body to the heatsink to get the best ground connection to the igniter itself. I sanded all points that are important to grounding and I made a small ground jumper to go from the igniter to engine ground that was already ran to the shock tower area.
03. Ignition Complete-Harness connected
In my quest to remove additional electronics that have control over a sub-system, I decided to use option 3 and go without my HKS twin power. I already got the PFC boost kit to get rid of my Greddy Profec B (which is amazing by the way) to allow the PFC master use to stock boost solenoid. As mentioned before I have already relocated my coils so installing the Complete-Harness was super easy. I removed the HKS twin power and my new coil harness. I installed the new Complete-Harness and connected it to the engine harness at B1-14. Jim did a great job at making this harness and it fit perfectly. The harness is the perfect length and the power and ground reach the battery / power source in the stock location. Since I have a rear battery, I am using the JP3 fuse box holder and I connected the Complete-Harness power here. I ran the ground wire to the threads near the diagnostics box. I did chase the threads and used a lock washer to make sure I had a good electrical connection.
The results - dude - wow.
The car has better throttle response at low rpm. I could definitely feel it was more punchy driving it around the block. It starts up just fine. I did rev it to 4500 to hear the difference in tone from when the 2nd turbo starts to pre spool and the exhaust note changes. When I had the HKS twin power the exhaust tone was louder and sounded like a hint of anti-lag, with the complete-harness it is still loud but its smoothed out. Maybe it's making less spark I don't know, but it sounds cleaner - I'll try to explain.
I'm going out on a limb here and I'm going to reference audio to give an example. When we add and amplifier to our radio to make our speakers louder, it will amplify everything even the noise and distortion. The radio source needs to be clean to have a better sound to amplify. The HKS twin power is going to amplify whatever it gets. So if the 12V coming through all the connectors and the ignition is degraded or affected by other electrical systems in use, is it possible the HKS twin power can be affected by this and not be able to amplify to its full potential? Is there amplified dirty spark vs clean spark? I know you will be able to see the difference on an O'scope. Regardless, If you use the Mini-Harness, this will get you battery power to the HKS twin-power and maybe it will perform even better.
I hope this is beneficial to those of you who are having ignition problems and what to try another option.
01. The "new" plug-n-play +12V ignition harness upgrade options
Last edited by rotaryextreme; Oct 5, 2025 at 10:32 PM.
The "new" plug-n-play +12V ignition harness upgrade options
The "new" plug-n-play +12V ignition harness upgrade options
The factory coils receive +12v power through the ignition switch, this is also shared with the fuel pump and the cars electrical system. One great upgrade to power the fuel pump is to switch the power source from the ignition to the battery via a relay. This is the same upgrade that has been done for the stock coils but now thanks to Jim we have a true plug and play harnesses.
The stock 12V pathway for the coils: Battery -> X-01 -> X-02 -> IGN/X-03 -> X-11 -> B1-14 -> Coils
Option 1. Mini-Harness 12V pathway: Battery -> Mini-Harness -> B1-14 -> Coils (can use HKS after relay)
Option 1 and 2 are very easy to use since you can leave the factory coil harness in place and just install the mini harness in between the engine harness and coil harness at connector B1-14. However for Option 2, if you have an HKS twin power you must connect it after the Mini-Harness since its performance will be affected by the relay. Option 3 requires the removal of the stock coil harness and you replace it with the Complete-Harness. Since the relay is built into the complete harness you cannot use the HKS twin power, but this option replaces your old wiring and gives the coils battery power without any additional connectors in the way. This is the way I went since I already relocated my stock coils to where the factory cruise control used to sit. OK let's get to the reason why the HKS twin power should not be used before any type of relay.
I wanted to know how the relay would affect the HKS twin power so I contacted Xavier of FC Tweak. The short answer is NO, the HKS twin power must be used after any relay and closest to the coil harness.
Here is the long answer. The Twin Power derives its name (Twin) for its dual function. Function (1): it resonates with each primary coil to convert the single ignition pulse from your igniter into a high frequency alternating current which transforms the ignition spark from a single shot spark to a multi-wave plasma (energy and dwell time remain the same but combustion efficiency and spark duration both increase and are especially beneficial at low RPM). Function (2) is its ability to add capacitance across the ground and main positive coil supply (common for all coils), thus charging up its internal capacitor while the coils are in their off state. When this capacitance is wired as close to the coils as practically possible, the energy stored in this capacitor will result in a higher 'punch' of voltage level during the coil on-time and hence increase the spark energy. If you wire up the Twin Power supply line before any relay, this capacitance effect will be cancelled by the extra inductance and resistance of the longer cable feeding the +ve supply of your coils, and hence kill all the benefits from function (2). Technically speaking, capacitive reactance and inductive reactance have opposite signs. So ideally the Twin Power should be wired up as close as possible to the coils, that's why it comes with an adapter harness which connects straight to the factory coil harness.
Too bad I cant edit the above post. The "Re-Cap" was me switching to option 2.
Copy paste error.
Here is what the "Re-Cap" Update 139 should have said.Bousou 7 - Update 139
Re-Cap
The "new" plug-n-play +12V ignition harness upgrade options
The "new" plug-n-play +12V ignition harness upgrade options
The factory coils receive +12v power through the ignition switch, this is also shared with the fuel pump and the cars electrical system. One great upgrade to power the fuel pump is to switch the power source from the ignition to the battery via a relay. This is the same upgrade that has been done for the stock coils but now thanks to Jim we have a true plug and play harnesses.
The stock 12V pathway for the coils: Battery -> X-01 -> X-02 -> IGN/X-03 -> X-11 -> B1-14 -> Coils
Option 1. Mini-Harness 12V pathway: Battery -> Mini-Harness -> B1-14 -> Coils (can use HKS after relay)
Option 1 and 2 are very easy to use since you can leave the factory coil harness in place and just install the mini harness in between the engine harness and coil harness at connector B1-14. However for Option 2, if you have an HKS twin power you must connect it after the Mini-Harness since its performance will be affected by the relay. Option 3 requires the removal of the stock coil harness and you replace it with the Complete-Harness. Since the relay is built into the complete harness you cannot use the HKS twin power, but this option replaces your old wiring and gives the coils battery power without any additional connectors in the way. OK let's get to the reason why the HKS twin power should not be used before any type of relay.
I wanted to know how the relay would affect the HKS twin power so I contacted Xavier of FC Tweak. The short answer is NO, the HKS twin power must be used after any relay and closest to the coil harness.
Here is the long answer. The Twin Power derives its name (Twin) for its dual function. Function (1): it resonates with each primary coil to convert the single ignition pulse from your igniter into a high frequency alternating current which transforms the ignition spark from a single shot spark to a multi-wave plasma (energy and dwell time remain the same but combustion efficiency and spark duration both increase and are especially beneficial at low RPM). Function (2) is its ability to add capacitance across the ground and main positive coil supply (common for all coils), thus charging up its internal capacitor while the coils are in their off state. When this capacitance is wired as close to the coils as practically possible, the energy stored in this capacitor will result in a higher 'punch' of voltage level during the coil on-time and hence increase the spark energy. If you wire up the Twin Power supply line before any relay, this capacitance effect will be cancelled by the extra inductance and resistance of the longer cable feeding the +ve supply of your coils, and hence kill all the benefits from function (2). Technically speaking, capacitive reactance and inductive reactance have opposite signs. So ideally the Twin Power should be wired up as close as possible to the coils, that's why it comes with an adapter harness which connects straight to the factory coil harness.
So there you go.
Option 02. Ignition Mini-Harness with HKS Twin Power Connected
My car has leaking coolant seals and makes it harder to start the car without the HKS Twin Power. Once it is running it's fine. I did have some trouble starting recently without the HKS Twin Power so I bought the mini-harness for myself so I could use the HKS Twin Power. Now I will use option 2 and use the Mini-Harness with the HKS twin power. I installed the new Mini-Harness and connected it to the engine harness at B1-14, then I connected the HKS twin power haness to the mini-harness, then connected the stock coil harness to the HKS twin power harness. The fuse and really are mounted on the same screw that holds the HKS Twin Power. Now the coils and the HKS twin power will get a voltage boost straight from the battery. Jim did a great job at making this harness and it fit perfectly. The harness is the perfect length and the power and ground reach the battery / power source in the stock location. I ran the ground wire to the threads near the diagnostics box. I did chase the threads and used a lock washer to make sure I had a good electrical connection. This is also proof of concept for C.Wan's car since he is running option 2 as well.
The results - great as expected.
The car starts up great and idles strong and smooth. I did free rev it and it seems to rev easier to higher RPM's. I have not driven it yet but I'm sure it will be good since the HKS Twin Power is now getting constant battery to amplify to the coils.
I need help. I have an addiction. I'm always finding excesses to buy something for this car.
I have been wanting sleek lights for a while.
Since I have the C-West spoiler I figured it would be ok to get the C-West sleek lights. I regretted not getting a near new set which was clean, but recently another decent set of C-west headlights popped up on e-bay so I got it.
I feel the Spoiler and the headlights are the hardest things to get. The body kit can be had a lot easier.
Yea, I have one of those problems too! Except now the name has changed from addiction to money pit at my house
The lights look like they have a lot of potential with a little elbow grease....
Yea, I have one of those problems too! Except now the name has changed from addiction to money pit at my house
The lights look like they have a lot of potential with a little elbow grease....
Those were the Ebay pics. When I got the lights, unfortunately they were not CATZ lights, all were no-name brand. The seller was really cool and let me return them. They are back on ebay. But there is also a new unused kit on ebay as we speak.
I ended up buying the R-magic type lights with LED light from Elite-TI.
I went to that link you put up, those are really cool looking lights, I've really never been a fan of the flip up lights on the FD. They look great when retracted
and bug eyed to me when in use. I'm in the process of trying to get mine running after a twin to single conversion, I'm definitely gonna upgrade all my lighting
starting with the rear lights but I don't want any junk or cheesey home brew looking crap on my car. I have spared absolutely no expense in this build, can't turn back now.
I'm gonna keep checking your build thread, update after you get your new setup installed. i'd love to hear how good the actual light performance is , I'm old, good head lights are very important to me as I love to go make a hard run at night when everyone else is at home asleep.
I went to that link you put up, those are really cool looking lights, I've really never been a fan of the flip up lights on the FD. They look great when retracted
and bug eyed to me when in use. I'm in the process of trying to get mine running after a twin to single conversion, I'm definitely gonna upgrade all my lighting
starting with the rear lights but I don't want any junk or cheesey home brew looking crap on my car. I have spared absolutely no expense in this build, can't turn back now.
I'm gonna keep checking your build thread, update after you get your new setup installed. i'd love to hear how good the actual light performance is , I'm old, good head lights are very important to me as I love to go make a hard run at night when everyone else is at home asleep.
100 percent!!! - on quality lighting.
I do like pop-ups, but these light work so well with my future build.
Im taking forever to build my car. When I have time Ill hook them up to a battery for you. I think Nathan has some pics. I need to get those too.
I received my Elite-TI R-Magic style lights and the exhaust bumper protector this weekend.
A+ Quality. It also comes with a PNP harness so it will work with the factory hi/lo beam controls.
They do not come with the clear lens so I will try to make some.
I might also try to open the window where the low beam housing is blocked.
I'll try to get power to them soon to see what the beams look like.
I'm sure fitment is spot on, but they will sit in storage for the next year or so.
Last edited by rotaryextreme; Apr 21, 2026 at 11:00 AM.
