Need help splicing old connector to new engine wiring harness

LAUREN DC CRENSHAW

MEMBER
2003 TOYOTA COROLLA
1.8L
4 CYL
AUTOMATIC
165,000 MILES

So I had a short in my old wiring harness and wasn't able to locate it and went to local pick a parts and pulled an engine wiring harness from a 2005 Corolla and was told it works for an 2003 Corolla. Well, for the most part they were correct except for the Neutral Safety Switch, and Throttle Body. The 2005 had one connector with all the wiring going into it and 2003 has to connectors for Throttle Body, and Neutral Safety Switch was a tad bit smaller and had 2 wires that were either missing from old connector for me to splice them with and don't know where they go into the old connector, but the wires/colors pretty much matched up but then again not sure if they are correct. I have looked at wiring diagrams and have tried to figure them out and just can't seem to. I would greatly appreciate if some one can break it down to noob terms for me. I am uploading pictures. The picture of the black, white, 2 light green, brown and yellow are the wires that went to Throttle Body connector and the picture of the connector is the Neutral safety switch connector showing the 2 empty spots and the 2 wires are a blue and a blue/red. I'm not sure if it's uploading any of pics. Added pics in reply!

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Monday, August 23rd, 2021 AT 4:57 AM

13 Replies

LAUREN DC CRENSHAW

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8 POSTS

Here are the pictures I was trying to upload with my question. Thanks in advance!

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Monday, August 23rd, 2021 AT 5:00 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi, Lauren.

The best I can think of to do for you is provide the wiring schematics for both model year vehicles.

The 2003 powertrain management schematics are 3 pages long. I had to cut each pic in half to make them readable for you, but I did overlap them. Therefore, the first 6 pics of for the 2003.

I highlighted the throttle body and the park/neutral switch.

Starting with pic 7, I attached the schematics for the 2005. They are 4 pages long, cut in half, so a total of 8. I did highlight the same things.

Here is a link you may find helpful:

Take care and let me know if you have questions.

Take care,

Joe

See pics below.

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Monday, August 23rd, 2021 AT 8:06 PM

LAUREN DC CRENSHAW

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Joe,

I'm a little confused on it still, I have been trying to understand it all but I still have something wrong. The one I know that is correct is reverse due to the light coming on! But I can now crank the car in all gears! The difference between the 05 and 03 wiring is that 03 D and N are not wired as with the 05 N isn't wired. So since mine is 03, I have to go with the 03 wiring correct? They only show a few of the wires and I get lost as what to do or how to know I got them all correct. I have the same colors matched and figured that's all I needed to do, but guess I'm wrong some where. So if you can break it down to simple noob terms for me Id really appreciate it. Thanks

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Saturday, August 28th, 2021 AT 2:59 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

Yes, since you have an 03, stay with that schematic. I attached both range sensors (neutral safety switch) below. They were the same, but I don't know if the new plug is pinned differently. When you place the vehicle in park or neutral, there should be no continuation of power. Those two positions don't signal anything. They create an open circuit. Something leads me to believe you have no power to that switch.

Both model years receive power via a red wire with a white tracer. Do you have power to that wire? If you do, when you shift to reverse, drive, 1, or 2, power is transferred through the switch to the appropriate circuit.

Check to confirm power, and then check the output from the switch. When in park or neutral, there should be no power out.

One question. Did the original harness have the blue wire for drive?

Let me know what you find.

Joe

See pics below.

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Saturday, August 28th, 2021 AT 10:00 PM

LAUREN DC CRENSHAW

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This is the original NSS connector from my old wiring harness, and they were 2 wires that weren't connected if I'm not mistaken, which would be the blue and blue/red. Have another question, I have the ECU from the 2005 corolla I pulled the harness from, should I be using that one or mine? I am going to go test the wires now. Here's something else the way I have it wired now I am able to crank it in every gear, but still wont turn over. I have had the battery on charger. I used starting fluid the other day and it went to start but didn't. So i'm going to try it now with battery charger afterwards.

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Monday, August 30th, 2021 AT 5:05 AM

LAUREN DC CRENSHAW

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Here is pictures of the switch. So I'm not sure if I did this right, but I did voltage test on wires having red connected to positive on battery and used the negative to each wire separately. It read 12.2 for just about every gear and every wire. Then when I connected to light green voltage dropped when I put it on light green wire and it was in low gear. Does this mean I wired it wrong or good?

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Monday, August 30th, 2021 AT 2:57 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

If you are getting output voltage to all wires regardless of the gear selected, are you sure the switch itself isn't bad? When you hit neutral/park, that should cut power.

I would keep the PCM that came with the vehicle. It is designed for your car.

Joe

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Monday, August 30th, 2021 AT 6:35 PM

LAUREN DC CRENSHAW

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Hi,

Here are the pictures of me testing each wire, and not entirely sure I did it right or set on the right setting. As far as I know the switch is good well it was good before engine swap, I think I may have it wired up wrong. When I was wiring them up I accidently bumped two into each other and the starter started to turn over, which surprised me. If I can't get it worked out today then I will take it back and try to get same year.

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Tuesday, August 31st, 2021 AT 4:00 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi, Lauren.

You've done so much work already on this. Not being there makes this really hard for me because I am jumping between multiple pages of schematics and your pics. By the time I get to the next schematic, I forget what was on the prior or your readings. Ugh.

For some reason, I feel the switch is shorted. I was able to find the diagnostics for the switch and CC I attached them below. Take a look through them and test that switch to see if there is a problem with it. They provide specific voltages based on positions. Let me know if they match.

Joe

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Tuesday, August 31st, 2021 AT 5:36 PM

LAUREN DC CRENSHAW

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Joe,

So here's the update, which might help solve my issue: Something was telling me to change out my main (100) fuse, and when I started to unbolt it, I noticed that on the inner side there were 2 bolts and a wire supposed to be connected to each bolt with a hollowed circular connector on each end and one was not where it should of been and was touching both pieces and this is where I found my wires had melted and touched each other. So I taped them off as best as I could. But haven't tried starting the car yet or anything. I wanted to try what you sent me but unsure of where it is located. Is it behind the speedometer or is that the ECU under glove box?

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Friday, September 10th, 2021 AT 10:29 PM

JACOBANDNICKOLAS

MECHANIC
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Hi,

Wow, there are a lot of bare wires. I'm not sure which one you are referring to. However, I copied a portion of one of your pics and circled something. Is that a fusible link? Also, which specific wire are you referring to?

If you look below, I attached 3 pics. Pic 1 is from your picture, pic 2 shows the ECM location, and pic 3 shows three wiring connectors that go to the ECM. Also, yes, the ECM is behind the glove box.

I hope this helps. Let me know.

Joe

See pics below.

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Saturday, September 11th, 2021 AT 7:37 PM

LAUREN DC CRENSHAW

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Joe,

So what I was trying to show you was the wiring that is under the relay/fuse box under the hood. Some how, something ended up shorting out(think old starter) and it went all the way to the wiring up under fuse/relay panel. I pulled it off to change main fuse(100amp) and that's when I noticed a few wires that were melted together and bare wires. So I wrapped them in electrical vinyl tape. Hopefully I did a good enough job. So this may be a reason as to why I couldn't get the car into gear, could be the reason why I'm having issues getting it started now, who knows. I not entirely sure if it is a fusible link, but I think it may be. I am going to try the voltage test hopefully sometime today, haven't had a chance because I've been working on a 2001 Chevrolet Malibu. But I am finished with it and just putting the last parts back on. I will keep you posted on readings. By the way thanks for all your help so far.

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Thursday, September 16th, 2021 AT 4:32 AM

JACOBANDNICKOLAS

MECHANIC
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Hi,

First, you are very welcome. Looking at the wiring, I'm surprised there wasn't a fire. As far as the fusible link (possibility), check to see if there is continuity from one end to the other. If it's bad, there won't be.

Let me know what you find or if there is anything I can do to help.

Take care,

Joe.

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Thursday, September 16th, 2021 AT 7:32 PM