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91 nsx power locks and alarm issues

16 October 2021
Hey nsx homies,

I’ve been reading about the nsx power locks / keyless entry issues on the forums. I have read about how guys are taking a system from an Acura legend and changing the connectors and making it work.

I just got my nsx a few days ago and I’m greatly enjoying it but I’d also like to get this electrical situation figured out.

I’d like to stay as oem as possible but I also just broke the bank buying the car so I’m not opposed to a cheaper alternative. (Amazon alarm with new fob route)

Here’s what’s going on, my fob obviously doesn’t work and neither do my power lock buttons. Sometimes when I park and take out the key the alarm auto activates. When this happens I can press the unlock button and alarm deactivates but the locks don’t unlock. Sometimes when I get out and lock the door with the key the alarm activates but some times it doesn’t.

I found a guy selling an oem brain and keyless entry system that’s plug and play for my car but it’s kinda steep.

Please let me know what my options are and how you think I should start!

Thanks a lot !

The car is a 91 and it’s RHD
alarm issues: there is a switch inside the door lock mechanism that gets corroded and becomes intermittent. The whole lock has to be removed from the door to get to the switch and it is not a fun or easy job.

You can unplug the Security Control Unit...you won't get theft protection though, but at least your horn won't be going off.

I have yet to find a RHD KA Legend that has keyless.

PM if you need help on RHD Keyless Units
A little back ground information would be of use. You said

Here’s what’s going on, my fob obviously doesn’t work and neither do my power lock buttons.

Since you refer to fob, I assume that means that you already have a keyless unit, presumably an aftermarket unit of some kind? You then made reference to looking at an "OEM brain and keyless entry system". I presume that means that you are thinking about purchasing an OEM keyless unit to replace what ever you currently have.

Some comments based upon those presumptions.

1) If you need information on the OEM keyless units, @drew is probably the current reining expert on that system.

2) Since you have a 1991, be aware that the interposing wiring harness changed sometime shortly after 1991 making the 1991 (and the 1992? - Drew can confirm) a one -off. If you get an OEM system meant for a later car it will not be plug and play. I think the controller will work fine; but, you will need to fiddle with or fabricate a new interposing harness. Drew can give you the scoop on those details.

3) Drew alludes to this. Even if your current key fob system is non operational the other problems you are having may also be related to other systems in the car . There is a good chance that just purchasing an OEM keyless unit and installing it will not resolve your problems.

4) You said
Sometimes when I park and take out the key the alarm auto activates.

Is that the OEM security system that is arming or is it your aftermarket unit that is arming. The OEM security system does not have an auto arm function. If you add the factory keyless unit it will add a relock / arm feature. If you unlock the car; but, don't open the doors the doors will relock and the security system will re arm in about 15 seconds. If the doors were not originally locked that relock / rearm will not take place. If the security system is auto arming without you locking the doors then whatever remains of the key fob system that is installed in the car may be generating a relock / rearm output for the security system.

5) Presuming that you still have the remains of whatever key fob system was in the car, I personally would be inclined to remove it and all the wiring associated with it if it was not OEM. Whether it is caused by bad design or poor quality installation, my opinion is that aftermarket security system installations are to be avoided. On removal you may discover damage to the OEM vehicle wiring which may need to be repaired.

6) If you have problems arming the security system, be aware that all of the security perimeter contacts (hood, doors, trunk ....) have to read closed. If one of those contacts is failing to read closed the system will not arm. The erratic operation with the lock / unlock switch on the driver's door may be a switch problem or it could be a problem with the door lock control unit. Does the passenger side switch operate the locks? The lock knob on the driver's door should lock and unlock the doors. It is a completely separate switch from the lock / unlock door switch. The lock knob switch will also arm and disarm the OEM security system.

Right now your description of the symptoms is way to loose to provide a definitive diagnosis. The problem could be whatever aftermarket system you have installed, the OEM security control unit, the OEM power door lock unit or the pile of switches and contacts that are tied into those two systems. My first step would be to remove / isolate whatever aftermarket system you have to see if that resolves the problems. If it doesn't, the next step is to get a copy of the 1991 factory service manual because you are not going anywhere without it. The service manual sets out test procedures for both the security control unit and the power door lock unit including pin input and output function tests. Based upon your limited description I would start with the power door lock system and then move to the security system. The electrical trouble shooting manual can also be useful; but, the factory service manual is more important because the ETS does not include trouble shooting procedures.
@Old Guy is correct and more information required

If @Champagnegsr would like to PM me, maybe send me photos and we can work this out and post back the results. It won't do the Forum much good as non-PnP systems are one-offs.

Model designation in JDM land are by model number and not year of manufacture.

The NA1-100's do not have an integrated SCU, but they do have this elaborate add-on OEM IR Keyless+Security Unit; which apparently *almost* worked and few/if any are in working condition today.

JDM NA1-110's and higher have an SCU and a different body side connector from NA1-100's and LHD cars.


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F/U: OP's car is a NA1-100 as indicated in another post. Which means no integrated SCU. OP may have the OEM add-on, an aftermarket, or both.

I've helped two others where an aftermarket alarm was installed trying to interface with the OEM NA1-100 add-on system and they are a kludge.

Here are the pinouts for LHD and RHD https://www.nsxprime.com/threads/91-92-keyless-solved.140311/#post-2008386