Main Relay differences

I noticed the part numbers are different for Main relays based on the year:

pre 1995: #39400-SL0-003 (link)
post 1995 #39400-SL0-A01 (link)

Seems like a bracket change probably due to the location change. Does anyone know if what is in the box is any different? I know that a 1995+ car will run with #39400-SL0-003 because that is what I swapped in to my car just now to get it up and off the side of the highway, I just want to know if I need to order the A01 part or if I can continue to use the 003 part.

Thanks!

yeap its the bracket on the back I have put a 2005 main relay into a 92 for testing worked fine.

5 years I know...but I'm asking the other way around: if you change the bracket, does a A01 (95+) main relay work in a 91-94? Shawn said he did so, anyone else?

Just 'sort of' ran into this with another member on another post. Honda changed the pin number references in the service manual between the 1991 and the 1997 service manuals (what was pin #1 in 1991 is no longer pin #1 in 1997). I checked a few of the pin numbers and despite the renumbering, the function of the pins on the relay that I checked remained the same. I went to my favorite site for checking part numbers, RockAuto, and pulled up pictures of the early and late relays (that is such a useful function). Here are photos of the pins on the relays.

Early relay pin arrangement


Later Relay pin arrangement



Based upon the photos the plugs on the relays appear the same and given that the pin functions did not appear to change despite Honda's renumbering effort, the early and late relays should be functionally interchangeable, which jives with the comments of others.

Early relay mounting with bracket



Late relay mounting




The late relay from Rockauto clearly does not come with the bracket. If you look at the later relay, the plastic retaining tab in the center of the bracket is slightly different; but, it sure looks like the later relay could fit on to the early bracket. Scaling the mounting relay case mounting moldings off of the photo might confirm whether the dimensions are the same. The other option might be to see if you can pop the cover and bracket off of your early relay and just transplant the guts of the later relay into the early case.

Interesting pricing on the relays. On the Rockauto site the early relay lists for $131 $Cdn. The later relay lists for $50 $Cdn. That would seem like sufficient motivation to try the later relay as a replacement on an early car!

Thanks very much for your details. I'll forward it to a friend for who I've ordered the (wrong) part for. I'm pretty sure the electronics are the same.

My fear was about the immobilizer system but I think that was introduced in 1997 but implemented in the ECU, not the main relay.

Correct. At least on North American cars there is no interaction between the immobilizer system and the main FI relay.

goldNSX said:

Thanks very much for your details. I'll forward it to a friend for who I've ordered the (wrong) part for. I'm pretty sure the electronics are the same.

My fear was about the immobilizer system but I think that was introduced in 1997 but implemented in the ECU, not the main relay.

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No question, all main relays are the same internally, only the bracket changed when they moved it to the passenger side mount.

HTH,
LarryB

I did it and just want to confirm that it works

Perhaps a keen observer can help me locate my main relay......

98 T Manual

It's left from the ECU, has been relocated back in 1995 or 1997.

goldNSX said:

It's left from the ECU, has been relocated back in 1995 or 1997.

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Well thank you.

Kind of interesting that it’s not mentioned anywhere; at least based on my research. Also. The parts diagram shows it on the right.

shern said:

Well thank you.

Kind of interesting that it’s not mentioned anywhere; at least based on my research. Also. The parts diagram shows it on the right.

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Your research must have been limited. A quick reference to the 97+ service manual shows it exactly where goldNSX states. There are links on Prime to free downloadable .pdf versions of both the early and 1997 and later service manuals. The .pdf copies are not 100% complete; but, what is there is generally the best source.

Get one - the service manual is your friend!

Old Guy said:

Your research must have been limited. A quick reference to the 97+ service manual shows it exactly where goldNSX states. There are links on Prime to free downloadable .pdf versions of both the early and 1997 and later service manuals. The .pdf copies are not 100% complete; but, what is there is generally the best source.

Get one - the service manual is your friend!

Click to expand...

Perhaps I should have mentioned I was referring to the parts catalog drawing.

Thanks for the help.