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 > Can someone help design a 5 volt circuit

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time2roll

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Posted: 04/25/22 11:54am Link  |  Quote  |  Print  |  Notify Moderator

Not sure where the lever and linkage connects but if the tunnel is that tight maybe a switch topside at the other end would work just the same.

Be very cautious with modifying the neutral safety switch. Could leave the vehicle stranded if it fails open or provide a lurching start for yourself or unknown user if something fails connected.


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Posted: 04/25/22 08:09pm Link  |  Quote  |  Print  |  Notify Moderator

If just adding a switch, I would recommend a momentary contact switch. That way, no one can accidentally flip it on, or accidentally leave it on. You have to physically hold the switch on for it to energize. Release it, and it de-energizes.


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2112

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Posted: 04/26/22 11:09am Link  |  Quote  |  Print  |  Notify Moderator

Have you considered having the neutral safety switch control a quality automotive grade DPST relay.

You might also consider placing a manual backup toggle switch across the contacts driving the starter solenoid in case the relay fails.

[image]

* This post was edited 04/26/22 03:37pm by 2112 *


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Posted: 04/27/22 12:16am Link  |  Quote  |  Print  |  Notify Moderator

Thanks 2112 I didn't even know that a double pole relay existed. I'll have to think about your suggestion as it takes the neutral safety switch out of the start circuit and relies on the relay alone.

I might have to decide that is good enough. Or I might have to put more thought into an added switch on the linkage.

* This post was edited 04/27/22 12:33am by opnspaces *


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Posted: 04/27/22 01:42am Link  |  Quote  |  Print  |  Notify Moderator

Amazon search
TYCO RELAY
They last 10 times longer than cheap Chinese garbage

2112

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Posted: 04/27/22 05:51am Link  |  Quote  |  Print  |  Notify Moderator

My understanding is you are trying to pull codes from a 1993 OBD1 EEC-IV controlled engine.

The neutral safety switch on the 1993 donor vehicle controlled pin 30 on the EEC. The EEC verified the neutral switch position on pin 30 prior to entering the self test mode. If the transmission was not in park or neutral it won't initiate the diagnostics sequence. Your 1977 vehicle does not have this feature. As you stated, the 1977 NSS controls the starter solenoid directly. The good news is you can force the EEC to think the NSS is controlling pin 30 by connecting EEC pin 30 to pin 46.

I assume you used the original 60 pin EEC connector during the swap and I hope you left some wire on each pin to splice onto. Not knowing what vehicle your '93 donor engine came out of the following are assumptions.

What you call 5V OUT should be STI on EEC pin 48. It's actually an input being pulled to ground to initiate the self test. Grounding this pin starts the self test sequence

What you call 5V Return should be Test Ground on EEC pin 46

Once you enter self test mode, the codes can be read as pulses on EEC pin 17

Are my assumptions close to accurate?

* This post was last edited 04/27/22 08:37am by 2112 *   View edit history

bighatnohorse

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Posted: 04/27/22 08:20am Link  |  Quote  |  Print  |  Notify Moderator

This might work: https://www.amazon.com/gp/product/B07TCF........_yo_dt_b_search_asin_title?ie=UTF8&psc=1


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Posted: 04/27/22 05:03pm Link  |  Quote  |  Print  |  Notify Moderator

Yes you're pretty much on the money. I initially didn't want to get to far into the computer details because I didn't want to cloud the waters or dissuade suggestions because it sounded too technical. So I left it as I have a 5v out and 5v return that I need to make work with my one old school NSS.

Donor was a 93 Mustang GT AOD automatic with a C3W computer. It was a complete swap, motor and harnesses but no transmission. It is smog legal in California with a BAR label on the door. I do have the extra wire available but unfortunately I did this swap 20 years ago and don't remember the actual pin numbers. I just have the two bare wires free under the hood next to the self test connector.

To pull codes I twist the wires together. Then I jump the STI connector to the diagnostic connector and read the codes from the blinking check engine light.

I'm assuming when you are talking about tricking the EEC into thinking I in park (that the NSS is controlling pin 30) that you're referring to me twisting the two wires together.

I've run like this for 20+ years with no issues. My hope is to design a system that when it's in park the EEC knows it's in park, and when it's not in park the EEC knows it's not in park. PLUS I need the NSS to safely control the starter solenoid.

I've received a lot of good ideas off this post and I'm going to try a few of them out on the bench and see what I can come up with.

Thanks for the ideas on the double relay by the way I really like that.

Thanks

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Posted: 04/28/22 07:44am Link  |  Quote  |  Print  |  Notify Moderator

You could bring all 4 wires to a DPDT rocker switch under the dash. Reach down and flip the switch while sitting in the drivers seat, turn the key and start counting flashes. Just remember to flip the switch off when done.

I had a '86 Mustang manual tranny, no MIL. The clutch had to be held down during the test while I counted voltmeter needle bumps under the hood. I volunteered my daughter to be the designated clutch crew. I could have rigged up something to make it easier but I only needed to do it a few times in the 15 years I owned it.

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