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Old 06-26-2011, 11:16 AM   #1
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Default CEL circuit?

1994 Miata. Reading up on installing MS, and there is one thing I can't find. I've searched, and most of what comes up is "install a timing curcuit" to activate the CEL at key on.

I do know that (at least around here) they will check for it, and will fail you if it doesn't come on. This is for OBD1 (no sniffer, no ECU hookup), and it's about the only thing they can check other than for a cat and some smog stuff under the hood. All visual, so they use that CEL as a way to fail you - and make you pay to have it fixed.

So, being that electronics is like speaking Martian to me, can someone point me to a simple way to make this happen? Does it / should it be wired to the MS, or just a simple key on power source? Is there a way for the MS to control this, or is that just needless complication?
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Old 06-26-2011, 11:32 AM   #2
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I happened to be reading my Link manual and came across the instructions to do this. It seemed to be not-Link specific, but just a general wiring change.

In some areas, emissions testing requires
that the Check Engine Light (CEL) illumi-
nates when the key is turned on. The 90-95
Link ECU does not do this, but a simple
modification can be made to the wiring
harness to illuminate the CEL. The 96-97
ECU operates the CEL at key on (and even
makes it blink when a knock event occurs),
so no modification is required.
For the 90-95 procedure, remove the glove
compartment. In the cavity for the glove
compartment there is a white electrical con-
nector to the right. In this connector are a
Yellow/Black wire and a White/Black wire.
Connect these two wires together. The easy way to do this is to use a modified Quick splice
connector to jump the two wires together. Now the CEL will illuminate when the ignition key is
turned to the on position and go out when the car starts.
Under section 11 of the Link Tuning PDF on the FM site. There's a photo that didn't copy/paste that helps clear things up.
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Old 06-26-2011, 11:37 AM   #3
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Thank you!

Exactly what I was looking for, but didn't think to look under other ECUs.

Once again, thanks!
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Old 06-26-2011, 02:43 PM   #4
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Ha, that works nicely. I hadn't cared before since I haven't gotten the car smogged with MS, but it's nice to have the CEL now just in case.

The .pdf on FM shows a tap splice but I hate those things so I just took a piece of antenna/magnet/winding wire, whatever you call it, and stuck it in alongside the pins in the back of the connector to jumper them. CEL is on with the ignition, stays on during cranking, goes off when the key is released to run.
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