LT1 Conversion will not shut off

[Badley]

Ok, so its taken me two years to almost complete my LT1/ 4l60E conversion. I fired it up for the first time the other day and it wouldnt turn off. I pulled the battery cable, kept running. Pulled the Alternator wire and it died.

OK so i figured the diode Ihad put in the wire from the alternator to the ignition must have been backwards. I open up hte harness and flip flop the diode. Car starts and will not turn off. I pull the battery cable and the car dies this time.

So I must have had the diode backwards the first time, but what else have I wired incorrectly to make it keep running with the key off?

[Samckitt]

Is your power to the PCM on a switched 12v source? I am guessing not, otherwise shutting off power to it would kill the engine.

[Badley]

Well I thought it was. I ran it off the origional hot wire to the distributor. The way I understood it i needed a wire hot with the key on start and run.

If you can tell me a better wire to run it from ill go and swap the lead out.

[Samckitt]

I had my factory harness reworked & on it was two wires I had to connect to a 12v source, one is hot with key on in the run & start positions, the other is hot all the time. I ran my keyed on wire from the fuse box.

[MonzaRacer]

While you may have a diode in the alt harness the 12 KO wire to distributor and the alternator must be on separate circuits. I have yet to make diode trick work consistently.
So what year and model was the LT harness from?
Oh yeah, pulling battery cable to shut it off, bad idea, if you need to kill it, pull power to ignition coil.
I have actually just used a heavy duty GM relay key switched to run the ignition coil power. The heaviest of GM relays are the Oval ones.

[Badley]

Monza,

The harness is from Sreet and Performance. Its a 95 setup.

The S&P harness has no provision for the Alt. I am usuing the Mad Enterpises Alt setup. I wired it up per Mark Hamiltons directions. The wire i put the diode in runs back into the junction block on the firewall with the rest of the cars stock harness.

[69LT1Nova]

Like Samckitt said, I also sourced my switched 12v from the car's fuse box. You are asking for problems by using the wire that fed the original distributor - keep in mind that this wire was for a points and condensor set-up and that it is a 20 gauge (dinky) wire with a built in resistance (not what you want for the computer). Also, that ignition wire is only 12v at start up, then drops to 6v! Wire the signal wire from a true 12v switched source.

I fought a long battle with that effing yellow ignition wire. I burnt it up the first time when I wired it to the starter (like original). Replaced the wire, then fried the starter solenoid. Turns out, I didn't need the thing! I cut it out, and all works great.

[Badley]

Im catch what yall are throwin at me. Can you give me a example of a true 12v switched source. I dont wanna go hacking away at my harness.

I replaced the origional dinky distributor wire with a 12 ga wire from the bulkhead forward. But i did not know that the volts droped down to 12.

[69LT1Nova]

PM replied. Happy wiring!

Yeah, that frigging yellow wire drops down to 6v after start-up so that the original ignition wouldn't fry the points. Go figure.

[69LT1Nova]

Found a pic for ya. (not my car)

Simple as a female crimp-on connector.

[Badley]

I switched it to the ignition slot on the fuse box. Same thing. I talked to Street and performance and they thought i was getting a backfeed from my fan relays... I unhooked them... Same thing... I unhooked my alternator...same thing... so the only thing left getting power was the fuel pump relay.... i unhooked it and ran it to the ignition slot on the fuse box along with the previouse wire and wah lah it started and turned off. My only question now is what is suppling my computer full time power. According to the tag on the fuel pump wire it says "to battery" and has a fuseable link. That wire also pigtails off to the ECU and I thought it was its constant source of power.

[Samckitt]

On Mine the PCM controls the coil side of the fuel pump relay. On the switch side one end goes tot he fuel pump & the other to the battery. It is two totally separate circuits, power from one side should not go to the other.

[Badley]

Ok so I got it figured out. I created my own problem because i assumed what a wire did. I mounted my computer in the trunk so i have a long harness. There was a wire in the harness that runs from the computer to the front of the car. The wire was labeled power to fuel pump. Well I thought i would shorten the length of the wire, so i cut it and ran it to a constant power junction block in the trunk, which worked fine. Then I got the great idea of powering my igniton from the junction box on the firewall. I decided to use a butt connector on the before mentioned cut wire, which I thought was just a through wire, and then tied it into the junction box on the firewall. Well come to find out, the power to fuel pump wire, recieves a positive feed from the oil pressure switch. The oil pressure switch serves as a backup system for the fuel pump in the event the fuel pump relay should fell. Any time oil pressure is above 5lbs, 12 volts are porvided to the to the fuel pump.

So what was happening was once the car started, the ignition wire was recieveing voltage from two sources. I would turn of the key killing one source but the oil pressure sending unit would continue to send 12 volts to the computer.

So lesson to be learned here:
1. Never assume anything, it always makes a a** of u and me.
2. Dont muck with someone elses wiring harness.

Thanks to all those who chimed in on this.

[Samckitt]

LOL, well at least you figured it out. There are 2 things I hate working with when there is a problem. One is computers & the other is electrical.

[MonzaRacer]

My big issue is working on aftermarket "custom" harnesses and not having proper diagrams to work from, get to be a bi***h after a while till you get a feeling for how it works,,guess it comes from working on cars all day too.