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Changing Main Relay?

Joined
27 July 2007
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Location
Denver, CO
So I decided to swap out my main relay. Figured it is easy enough. Here is what Honda sent me:

2012-03-25_17-54-37_303.jpg


And here it is next to my original relay from my 1991 NSX:

2012-03-25_17-51-20_752.jpg


Ummm..... that doesn't look right. Help? :)
 
They sent you the main relay for a '95-05 NSX (part number 39400-SL0-A01). The correct part number for the main relay for a '91-94 NSX is 39400-SL0-003 which looks identical to the one on the right in your second photo.

Incidentally, I have an extra '91-94 main relay that I'm about to post for sale. It's used but known to be good. I'm about to post it for sale on this forum's classifieds. If you're interested, PM me and I can send it out tomorrow.
 
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The Main Relays for DBW and Non-DBW model
I'm guessing by your info you have a 1991 - therefore you are non-DBW.

the internal circuitry is the same, infact in the early 90's they upgrades the spring to a metal plate in the coil.

Also for the DBW cars, you'll notice that they relocated the main relay to the corner of the car near the passenger B-pillar, and different bracket too.
 

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Drive-by-wire

the cars from 1991 to 1994 used a cable to activate the throttle, the cars from 1995 and up used electromechanical actuators setup to do that, no cable ! Sometimes called ECT - Electronic throttle control.
 
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Drive-by-wire

the cars from 1991 to 1994 used a cable to activate the throttle, the cars from 1995 and up used electromechanical actuators setup to do that, no cable ! Sometimes called ECT - Electronic throttle control.

Wouldn't it be ETC for Electronic Throttle Control? :wink::biggrin:
 
Thanks guys. Ken, my old relay is working fine. I'm replacing for preventative reasons, so I want brand new.
 
Thanks guys. Ken, my old relay is working fine. I'm replacing for preventative reasons, so I want brand new.

Wow...replacing a main relay for preventive reasons? You're a better man than I! As a general question for the forum...and since I've got a '91 with its original main relay, is this a part that would be considered a "wear and tear" item?
 
Wow...replacing a main relay for preventive reasons? You're a better man than I! As a general question for the forum...and since I've got a '91 with its original main relay, is this a part that would be considered a "wear and tear" item?

Common failure, order one while you can, especially the 1991-94 verison.

Paul,

Swap the bracket, call it good;).

Regards,
LarryB
 
Wow...replacing a main relay for preventive reasons? You're a better man than I! As a general question for the forum...and since I've got a '91 with its original main relay, is this a part that would be considered a "wear and tear" item?

Yes, but you can just resolder the relay connections to the board, as is well documented elsewhere on the forum. Worked for me... :smile:
 
Wow...replacing a main relay for preventive reasons? You're a better man than I! As a general question for the forum...and since I've got a '91 with its original main relay, is this a part that would be considered a "wear and tear" item?

YES , all hondas ,not just NSX , I replaced mine as soon as I bought it (08)
call it preventive maintenance
 
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YES , all hondas ,not just NSX...

Yes, true... I had two Accords and both had failed main relays -- one at 95k, one at 150k.... I just carry a new relay in my NSX tool kit in case I ever need it.
 
Yes, but you can just resolder the relay connections to the board, as is well documented elsewhere on the forum. Worked for me... :smile:
I did the same removed a working M. Relay for preventative maintenance reasons, took a look under a magnifying glass at the relay solder traces, and sure enough there were cracks starting but not all the way through the trace from side to side. Re-soldered and cleaned the flux off and took another look with the magnifying glass. Like new. Re-installed.
Yes, I am cheap!, but I trust my soldering work. I worked on a microwave Electronics repair bench for Hewlett-Packard for 10 years.
 
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Yes, but you can just resolder the relay connections to the board, as is well documented elsewhere on the forum. Worked for me... :smile:

Yes, this is true, but I will caution everyone, this is not the only failure. The actual relay contact will burn also, over time. I have "fixed" this with resolder, but then needed to replace it later. So I always replace them now.

Also given the fact the cars are now 20+ years old, the parts will get harder to get in the future.

My $.02

Regards,
LarryB
 
Yes, this is true, but I will caution everyone, this is not the only failure. The actual relay contact will burn also, over time. I have "fixed" this with resolder, but then needed to replace it later. So I always replace them now.

Also given the fact the cars are now 20+ years old, the parts will get harder to get in the future.

My $.02

Regards,
LarryB


Is this for all NSXs or just the earlier year?

I might just replace mine just for the fun of it
 
Is this for all NSXs or just the earlier year?

I might just replace mine just for the fun of it

All NSX and most likely all Honda/Acura. More common in older car due to age. I just order one and put in my nsx parts collection for future use :biggrin:
 
If you read some posts on the UK forum you will find a lot of information about this issue just look for 'Kaz' his 57 page thread is more than informative i would consider it a mandatory read for those that want some good info on maintenance it's not hard.
Replace the main relay with the new one or at the very least get a new one and carry it around the newer models work on all years they do break.
 
All NSX and most likely all Honda/Acura. More common in older car due to age. I just order one and put in my nsx parts collection for future use :biggrin:

I've done the same , I have a mini stock pile of things that I'm gonna need in the near future...
 
Yes, this is true, but I will caution everyone, this is not the only failure. The actual relay contact will burn also, over time. I have "fixed" this with resolder, but then needed to replace it later. So I always replace them now.

Also given the fact the cars are now 20+ years old, the parts will get harder to get in the future.

My $.02

Regards,
LarryB

I repaired mine in april, it went out again yesterday. My 1st expierence was after driving 4-5hrs to run on a airstrip and as soon as it was time to run, the car wouldn't start, rather frustrating. The 2nd time, as Johnnymo mentioned, I tapped it a few times and car started. I will buy 2 2moro for backup.
 
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I'm having a starting issue myself: my (crappy) battery charger set to car-start mode sent too much juice into my electronics and something fundamental popped. In fact, I distinctly heard a rapid "click-clack" repeatedly for ~5 seconds until it just stopped, then nothing. That behavior screams relay (or fuse).

Non-ECU accessories all function normally, but IG "on" doesn't light up the instrument cluster and anything else related to engine management + starting doesn't work. In previous 90s-era cars I have worked on, this was almost always indicative of a relay or ECU on-board issue.

I have carefully reviewed all the fuses that I can find in the main 3 boxes. Its never that easy.

I have checked the starter cut relay, removed and visually inspected the ECU itself, and tested some of the basic connections for continuity. All appear normal.

My literature review has led me here, and PGM-FI main seems like it is close enough to battery that it could be the culprit in my case. I removed it and examined the solder/board, definitely getting some burn/discoloration on the backside of the board on both sub-relays.

I can't find any other relays that would be so fundamental to "key-on" operation that most of the car is dead. Any other places I should check? Sounds like I should grab an extra PGM-FI main to have around in any case...

Tapping the knowledge base: when main relay fails, does the Instrument cluster not activate (or rather, could this happen)? In most things I've read, people still can get the starter to crank, but I get nothing. Most curious.

Apologies if I have missed a key thread with more answers.
 
^ +1. This is a lazy answer because I didn't go look at the ETM circuit diagrams, but could it be the ignition switch - another item prone to failure as these cars age?
 
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