Nb Miata Main Relay Diagram

Larry Koh created this post in the Maxxis Cup Supermiata facebook group about his son Kyle's Maxxis Cup car. I thought it would be good info to share.
Keith Tanner chimed in that he virtually lost the Targa because of this same failure.
-Emilio

Might want to inspect your main relay.

As some of you know, Kyle Koh broke twice at Big Willow last Saturday with electrical failure. First of all, a big thank you to William Chen, Jerry Awesom, Alex Renderos, Sonny Watanasirisuk, and everyone else that helped us.

It was as if the ignition switch was just turned off while driving. Crank, no-start. Ultimately what we found was that our main relay in the engine power distribution box had failed. My first reaction was that this was a 25 year old relay that had been in use for presumably ~125k miles, so this may be the reason for failure. I called every auto parts store from Palmdale to Mojave with no luck. William came to the rescue and borrowed Jerry�s main relay, as he was done on track for the remainder of the day (another story). Kyle used the relay for qualifying (P5), but at the end of the session the same failure happened. Turns out we killed Jerry�s main relay as well.

William to the rescue again, giving his own relay after the race to Jerry so that he could drive home. Thank you again, William. New relays for both of you are on their way from Mazda. Message me your addresses, and I�ll send them later this week.

Now, what happened? I�m waiting for the relays to arrive for further testing, but after studying the failed relays and the wiring diagrams that I could get my hands on, I�ll share what I know now, so that others don�t suffer the same fate, although knowing what I know now, I could have made a modification, and Kyle could have finished the day (shhhh, don�t tell him that).

The bottom line is that continuously high current flowing through the relay caused the load side contact to heat up and melt the plastic which allowed the contact to separate enough to cease current flow, which is akin to shutting off the ignition switch. What caused this? Well, my suspicion, which I�ll verify once the new relays arrive, is the recently installed AEM 50-1200 E85 fuel pump, as that�s the only high current consumer that I can find on the wiring diagram (current actually goes from the main relay to the �circuit opening relay� to the fuel pump). Most of the direct outputs from the ECU are low current (as you might expect from a solid state component). I�ll check the actual current consumption as soon as we�re up and running again. Might need to relay control the fuel pump a different way, or look for a different fuel pump altogether.

When we couldn�t get William�s relay out of his box, we removed Alan Tseng�s. I found it was quite hot when I removed it. We ended up getting William�s out, so ultimately used his for Jerry�s car, and I didn�t find his as hot, so maybe this is an NA thing? Nevertheless, if you use a fuel pump other than a bone stock one, or your relay is original, you may be setting yourself up for the same fate that we experienced. Also, it�s likely to happen over a period of time, and we just finished off Jerry�s relay which was older than ours by ~75k miles. Look at the photos, and you�ll see what I mean. Our relay wasn�t as bad as Jerry�s, but it still didn�t allow current flow through the load side.

The inspection is simple. Remove and inspect the load side pin on the bottom of the relay. If there is any sign of melted plastic, or the pin isn�t perfectly parallel to the adjacent pin, you should replace it. I would. As far as I can tell, the Denso B6S8, and the Imasen B5B4 relays are the same, although I will dissect the B5B4 when they arrive later this week and report that as well as the actual current flow of the fuel pump.

Also, if anyone has any other wiring diagrams or experience with main relay failure, or any other common failures, please comment. I�m constantly learning about our car, and knowledge is power. Just thought this information might be useful to others.

Source: https://www.miataturbo.net/general-miata-chat-9/main-relay-failure-91002/

Posted by: scottresitsesz.blogspot.com

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