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Discussion Starter #1
Usually dont post questions but I cant figure this out.

1990 Tbird SC. When I turn the key and try to turn the motor over, the entire car dies. No lights, door chimer stops, whole car goes flat. BUT if I turn the key back into the off position, it works. Already changed the ignition slide switch, still having the same issue. Using a volt meter I cant find anything that stands out. Anyone have ideas, or run into something similar? Car was complete fine yesterday.

Yes it has a 5.0 in it now but the body harness, including ignition wiring and distribution box, hasnt been touched. And currently the power wires for the 5.0 are disconneted so that shouldnt be messing with it.

Also have times where the car stays dead until I jump the starter solenoid, then the motor kicks a bit and the car has power again. But again, I havent cut or spliced any wires into the car, so its all stock wiring. Trying to get the car started so I can move on with the project.
 

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Are the battery cables clean and tight? I get this issue on my GP when one of them works just a bit loose.
 

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Are the battery cables clean and tight? I get this issue on my GP when one of them works just a bit loose.
Double checked and they are good. Tested the battery and its good. Thanks though.

Its weird and driving me nuts. When the key is out and you open the door, everything works. Turn it the key down into accessory, and the windows and lights work. But the moment you turn the key into Run or start, it dies. Like nothing works at all. And again, already changed the ignition switch.

What is kinda funny is the auto seat belts work now. They didnt when I got it.
 

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Let’s backtrack from here. So the car would start and run yesterday and today it won’t. Did this happen out of the blue or was there something you were working on on it in the interim where these key positions suddenly didn’t work?
Car hasnt run yet, but the car would atleast try to start or id be able to have the radio on. Only thing electronic wise I did yesterday was hook in the extra junction box thatll power the fan, fuel pump, and PCM. And I hooked it up on the same peg on the starter solenoid as the cars factory box. After that the car would die when I turned the key. Removed the extra box and still dies. Changed the ignition switch and it dies. Also, since a couple hours passed, I changed the starter solenoid on the fender since I messed with that with the extra box. Still dies.
 

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When you changed out the ignition switch, was there any sign of burning on the connectors? I have seen those get brittle and crack before, and cause weird power delivery issues due to poor connections.
 

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When you changed out the ignition switch, was there any sign of burning on the connectors? I have seen those get brittle and crack before, and cause weird power delivery issues due to poor connections.
No, connector was in good condition.
 

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Only thing electronic wise I did yesterday was hook in the extra junction box thatll power the fan, fuel pump, and PCM.
So this junction box is not hooked to these things yet? This is additional to the original setup, but not connected to anything?

If this is incorrect, list what it's tied to.


And I hooked it up on the same peg on the starter solenoid as the cars factory box. After that the car would die when I turned the key.
This is the output side of the solenoid on the firewall or the input side, that comes directly from the battery?

Where is the "Always on" power to the EEC connected?


Removed the extra box and still dies.
Something was either disconnected, or you've blown a fuse or fusible link. The system changed when you added the box.
Find what changed.

Check the fuses that are "Hot in Start or Run" as well as the terminals on the ignition switch.
The terminals go to a connector you can measure.

I don't have a wiring diagram for those years, so I can't help.

Changed the ignition switch and it dies.
The problem is in the wiring that was affected by the change by adding the original box.

Also, since a couple hours passed, I changed the starter solenoid on the fender since I messed with that with the extra box. Still dies.


Check the wiring diagrams for the connections to the "Hot in Start and Run" circuit. From the Ignition Switch, it should be Red with a green tracer; They're usually the same color between years.

See if Circuit 38 BK/O is live at the switch; it's on multiple terminals, see that all are live. It's the battery input.

Fuse 13, 15, or 17 may be bad, in the underhood box, if it's the same as a 96, lol.
Circuit 38 is on fuse 17, and it's a 60A fuse.


There are fuses, and Fusible links; the fusible links are in the wiring loom, and may have taken out other wiring as well.

Check the megafuse.

The problem goes back to the original addition of the "new" box to the power; it's fried something it's connected to, and you'll have to find it.
 

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Discussion Starter #9
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So this junction box is not hooked to these things yet? This is additional to the original setup, but not connected to anything?

If this is incorrect, list what it's tied to.




This is the output side of the solenoid on the firewall or the input side, that comes directly from the battery?

Where is the "Always on" power to the EEC connected?




Something was either disconnected, or you've blown a fuse or fusible link. The system changed when you added the box.
Find what changed.

Check the fuses that are "Hot in Start or Run" as well as the terminals on the ignition switch.
The terminals go to a connector you can measure.

I don't have a wiring diagram for those years, so I can't help.



The problem is in the wiring that was affected by the change by adding the original box.





Check the wiring diagrams for the connections to the "Hot in Start and Run" circuit. From the Ignition Switch, it should be Red with a green tracer; They're usually the same color between years.

See if Circuit 38 BK/O is live at the switch; it's on multiple terminals, see that all are live. It's the battery input.

Fuse 13, 15, or 17 may be bad, in the underhood box, if it's the same as a 96, lol.
Circuit 38 is on fuse 17, and it's a 60A fuse.


There are fuses, and Fusible links; the fusible links are in the wiring loom, and may have taken out other wiring as well.

Check the megafuse.

The problem goes back to the original addition of the "new" box to the power; it's fried something it's connected to, and you'll have to find it.

The additional box ONLY runs the EEC, fuel pump, and fan. The stock EEC and IRCMI were removed before I got the car. But since the lights, horn, and in general the car worked without these things, i didnt want to mess with the wiring in the car cause it worked. Guess thats the irony in this.

With the new engine, trans, and computer, I decided to get the junction box from an explorer (where the motor and EEC are from), thin out what I didnt need (abs, lights, wipers, ect.) And add it to the car. The explorer junction box uses a thick grey wire to power the box, similar to the SCs. So I hooked it on the same peg on the solenoid. I believe the input side, cause it has 12.7v all the time.

Ill douple check but the fuses under the dash and under the hood but they tested fine, and those that I couldnt because of the key issue I removed and they arent blown. If what I have read is correct the 90s didnt have a mega fuseb but a bunch of fusible links. Been trying to locate them.
 

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You're gonna need the wiring book from the original car, and the Explorer you cannibalized.

The answer you gave me doesn't help; Answer the details, with the parts I asked them, and I might be able to help.

Generalizations aren't helpful, when you're talking circuitry.

Check the colors of wires I mentioned, and report back. :)
 
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