MLeopard

There is no reason a soldered connection should have any more or less interference than a crimped connection. Just make sure the shield is continuous and terminated as it should be. Soldered connections must be properly strain-reliefed or, yes, they may break at the joint but the same strain that causes the wires to break can cause a crimped joint to become loose. Loose crimps can corrode or become intermittent in their connection and be a headache to troubleshoot.

You're correct that the factory merges are crimps but they are also much nicer crimps than what one typically sees in hobbyist auto wiring.

Bottom line, either will work if done to proper levels of workmanship. If Kahn is doing his soldering to the level he has done the rest of this build he should have nothing to worry about.

KahnBB6

iTrader: (5)

^^ I can confidently say I have been careful about making securely tied connections (not balled ties of wire) before applying just enough solder to fuse both wire bundles prior to the heat shrink. Those connections are not coming loose, nor are they covered in big globs of solder. Nice and neat on each one. I have seen some of the unique factory crimps that Toyota used in order to split some wiring connections and I'd love to have a mess of those and whatever special crimping tool they used but it looks very proprietary for such small crimps.

...

On the note of my current research, I think I have figured out how to get TE2 at the diagnostic connector wired, assuming ALL I actually need is to put that wire into the diagnostic port under the hood into the Lexus SC IK1 Pin #2 location. I have to assume that since the rest of my car's body harness is wired for OBD1 diagnostic controls that is all I need to put in place. The MKIV TT OBD1 wiring diagram seems to suggest this if I understood it correctly. Hope I'm right?

I am assuming the same about the MKIV IJ1 Pin #8, Blue/Red wire (“FUEL FP DIAGNOSIS POINT”) to SC300 IJ1 Pin #1. I am guessing (and this is not a very educated guess on my part) that all I really need to do is to put a wire/electrode end there on the engine side Diagnosis port and run that wire through the loom all the way to SC300 IJ1 Pin #1 to make the appropriate connection.

Less clear is what to do about the Theft Horn wire, although I did find that in the schematic... but I'm not sure if I was looking at MKIV body harness wiring schematics or engine loom wiring schematics for that one. I can run a wire for that but I am still not sure what on the MKIV engine harness it should ultimately connect to.

MKIV IJ1 Pin #5 (“TO DIAGNOSTIC BLOCK TE1”) to SC300 IK1 Pin #4... now there is a brown wire for that one in the pre-described location (the MKIV wire should have been yellow/blue)... and I COULD just solder that... but since I am concerned at this point that I am actually dealing with OBD2 wiring that I want to convert to OBD1 wiring I need to open up the diagnostic connector to see if that TE1 pin indeed has a brown wire. Since my continuity test of MKIV IJ1 Pin #5 and Diagnostic Port TE1 did not bear fruit I am concerned the TE1 wire may go somewhere else.


Those and the Heater VSV and A/C wires that have to be run... and the one big 14 gauge wire I will need to run to EA-2 behind the battery in the engine compartment for Lexus SC300 IJ1 Pin #12 (“FUEL PUMP B+”)... hopefully I will not be missing anything else that is critical.

I have also learned that OBD2 MKIV TT wiring harnesses use an additional ground for either the front or rear O2 sensor to be heated, whereas my OBD1 setup should not have this for correct function and emissions performance. So I will have to figure out where this additional ground is on the MKIV harness (I think?) and eliminate it so that my OD1 ECU doesn't have an issue or foul my O2 sensors by running rich.

gerrb

iTrader: (34)

Craig - I believe I haven't answered you last text messages ... been busy playing with grand kids .

Just to confirm :

Diagnostic Port TE2 goes to IK1-2 (SC Plug) and goes to Pin 19 of the 40 pin ECU Connector

Yes FP Diagnostic pin goes to IJ1-1 (SC Plug)

Theft horn wires ... they go only from IJ1-4 and IJ1-9 (SC Body plugs) to the horn. They have nothing to do with the engine harness (MKIV harness)

Diagnostic Port TE1 goes to IK1-4 (SC Plug)

Note : As I have suggested .. don't rely on wire colors , you can be misled .

KahnBB6

iTrader: (5)

Thanks Gerry! No worries-- family time with the grandkids is golden time!

Thank you for confirming those!

I know I can get the missing Diagnostic Port TE2 wire routed to SC IK1-2 but is it a split connection that also joins it to the 40-pin ECU Pin #19? If so I should need to find Pin #19 or if there isn't one on this harness... add one from the cannibalized SC harness) to join to that TE2 diagnostic port wire.

FP Diagnostic pin -- got it! I will have to figure out how to get the IJ1-1 connected to that.

Theft horn wires -- If they are not part of the MKIV harness, do I have to find the wires they connect to from elsewhere under the dashboard footwell? Or run wires directly to the horn?

Diagnostic Port TE1 -- I am bothered that I have not been able to continuity test confirm that pin on the Diagnostic Port to MKIV IJ1 Pin #5 but otherwise regardless of the wire color I would just solder it and be done with it. Still, if I have to unwrap the harness to address the other wires then I will double check this one to make sure MKIV IJ1-5 is actually routed there already.

Yes-- I have tried to note the wire colors as being accurate to the guide whenever possible but I have *only* made my soldered & confirmed connections to the SC body plugs based on the MKIV pin location as prescribed and not based on whatever the color of the wire is.

I need some generous lengths and gauges of braided/insulated wire at this point so I will see if I can buy that from a local electronics store tomorrow.

gerrb

iTrader: (34)

yes it's a split on the TE2...there is a wire on that harness...ij1-17 mkiv plug... move it to the sc ik1-2

there are theft horn wires on that mkiv harness going to the bay

KahnBB6

iTrader: (5)

On my MKIV harness there is no IJ1-17 pin or wire at all. There is also no pin or wire on the Diagnostic Port in the TE2 location. Just blank pin locations where they should be. I am having to create the entire TE2 wiring path from scratch with lengths of wire I am cannibalizing from my spare 1997 SC300 Auto harness. (Note to anyone reading: the project car is a 1993 SC300 and the intention is to stay OBD1. I am just using wires, pins and connectors from a spare 1997 SC300 Auto harness and re-pinning the body plugs for my '93 OBD1 SC300).

I have enough length of clean wire from that other harness to create the main TE2 path to SC IK1-2. Then, as you've said, I will need to solder a second wire from that junction into the 40-pin ECU connector at Pin #19.

I also have no "FP" pin on my MKIV Diagnosis port. Like the TE2 location, it is just a blank space with no pin/wire. So I have to run a length of wire for that one as well to get to SC IJ1-1... however does that connection also get a spliced into another ECU connector pin location as well? There is just a blank space at the MKIV IJ1-8 (Pin #8) location as well. There is a black with red striped wire just below that space in what *should* be a totally unused location but I have no idea what it does and I can't yet trace it to anything.

If there are Theft Horn wire(s) on this MKIV harness they are not at MKIV II1-22. There should be a wire there but on my harness it is just a blank space with no pin/wire.

All of these missing pin/wire locations aren't due to anyone having messed with the harness. I see no evidence of that. This far back into the harness... no one has touched any of this or the original electrical tape and insulation since this harness left the assembly line.

The missing Diagnosis Port pins FP, TE2 and the TE1 wire that doesn't take to a continuity test at MKIV IJ1-5 are why I am thinking I may actually have a 1997 MKIV 6-speed harness set up for OBD2. I know they aren't supposed to be different in terms of USDM TT ECU control but since I have already come this far my goal is to revert the harness for full OBD1 operation, including for the operation of both TT OBD1 O2 sensors. I know that an OBD2 MKIV TT has an extra ground wire for one or more heated O2 sensors but I am sure that would negatively affect the an OBD1 TT O2 sensor with an OBD1 TT ECU controlling it.

I can't think of any other explanation for the missing Diagnosis port pins since all the OBD1 cars were supposed to use both TE1, TE2 and FP and B+ for diagnostic testing, correct?

gerrb

iTrader: (34)

after inspecting both odb1 and odb2 harnesses of a supra mkiv from the TIS (Toyota Information System) website where all Toyota / Lexus cars info are accessed and confirmed with another automotive maintenance vehicle information source website :

* Either it is an ODB1 or ODB2 , TE1 diagnostic port goes to IJ1-5 (mkiv plug) and repin to IK1-4 (sc plug) . If you don't find a wire on the mkiv plug then that had been modified.

* on ODB2 mkiv harnesses , there is no TE2 diagnostic port wire

* on ODB2 mkiv harnesses , there is no FP diagnostic port wire

* either it is an ODB1 or ODB2 , theft horn wires -> one goes to the 15A hazard / horn fuse and the other one goes to pin 19 of IB6 (mkiv ...check the diagrams I sent you buddy) ... move them .

KahnBB6

iTrader: (5)

Thanks for confirming for me Gerry! This has been throwing me for a loop!

I do have a TE1 wire on this MKIV harness but it doesn't pass a continuity test to MKIV IJ1-5. I think... maybe I should run another wire in its place along with the others just to be safe and leave the existing TE1 pin out.

There were no TE2 or FP diagnostic wires but upon unwrapping the harness up to the Diagnostic Port wiring area there is no way this harness was ever modified and put back this neatly and carefully. The tape itself is too old and worn in some places. It has to be an OBD2 6-speed harness that I have and not an OBD1. The wires that are missing couldn't have been removed and the entire harness re-sealed this well.

What I am doing at this point is converting what I am pretty sure is a USDM OBD2 1997 6-speed harness (since '96 MKIVs had no 6-speed option) into full OBD1 spec. The operations for the ECU, as far as I understand, are exactly the same as OBD1 so I should not need to change any ECU pin locations. The extra ground for one of the O2 sensors that is present on OBD2 I know I will have to eliminate but I think I have a guide for that... so long as the wiring for that one ground wire isn't very deep into this harness.

For the Theft Horn wire since it has to connect so far up in the harness at the front of the engine I am thinking it may be best to run a long wire for that along with the 14 gauge wire I will need to connect Lexus IJ1-12 to direct Fuel Pump B+ power.

Right now I am wiring in the following:

-- TE2 wire on the Diagnostic Port for Lexus IK1-2 & Pin 19 of the 40-pin ECU connector

-- FP wire on the Diagnostic Port for Lexus IJ1-1

-- Heater VSV wire Red/Blue & Ignition PWR to A/C ECU Red/Blue to Lexus IJ1-2

-- Heater VSV Black/Yellow to Lexus II1-7

-- Replacement wire for the existing TE1 Diagnostic Port wire which I do not trust because I cannot get a continuity test to confirm its connection to MKIV IJ1-5. If that one also has an ECU connector splice then maybe that is the reason? I am going to double check a 1997 MKIV TT OBD2 wiring diagram for TE1 to see how it differs from the 1995 MKIV TT OBD1 wiring diagram containing TE1.

Then after that before fully sealing the harness again I will:

--Run a long brown wire (not sure of the gauge needed) from EB1-7 in the engine compartment's Ambient Temp Sensor through the cover of the harness to Lexus II1-1 (splice in with the brown A/C Lock Sensor at Lexus II1-1).

--Run a long Red 14 gauge copper braided insulated wire from EA-2 near the battery through the cover of the harness all the way back to Lexus IJ1-12. I will use a weatherproof pull-apart connectors for this at the battery area. Edit: I have located the same original thick gauge wire from the Lexus harness (unfortunately I cut the wire already about 12 inches from the connector spade) and I may just try to remove as much of that length as possible from the spare/cannibalized 97 SC300 Auto harness... but it may not be enough length for this purpose.

--Run a long wire (unknown gauge but maybe 16?) from Lexus IJ1-9 all the way into the front(?) of the engine compartment to splice into the existing Lexus horn wiring.

--Locate the correct OBD2 O2 sensor ground wire to eliminate

And apart from finding the correct O2 sensor ground wire to eliminate I think... I think... that should be it?

KahnBB6

iTrader: (5)

I have traced the original Diagnostic Port TE1 wire on this harness directly to the 40-pin ECU connector at Pin #20. No spare splice wire that would allow it to connect to any MKIV body plug. I know it has to be connected to Lexus IK1-4 but should that Pin 20 connection to TE1 also remain to allow it to operate on OBD1 function?

Edit: What I am seeing in the MKIV Supra OBD1 1995 wiring diagram is that TE1 should remain connected to the 40-pin ECU connection at Pin #20 but that it should indeed splice into its native MKIV IJ1-5 (and thus for my SC it splices from there to also join SC IK1-4).

Also on this harness it is not a Yellow/Blue wire but is instead a Yellow with Green Stripe wire.

KahnBB6

iTrader: (5)

I'm getting there.

I followed the reverse of the instructions in this thread: http://www.supraforums.com/forum/sho...D2-ECU-Upgrade

...in order to convert the MKIV harness to OBD1 function. Every single wire change required for that DIY was consistently in the place that an MKIV TT OBD2 computer would have needed it be from the factory and every pin that would have been used for OBD1 on the ECU connectors was consistently blocked off with little plugs.

So doing the reverse of all that thread's instructions effectively changed the original OBD2 wiring to OBD1 wiring.

I changed those, added FP and TE2 wires to the Diagnostic Port, traced TE1 to the correct Pin #20 at the ECU connector and tomorrow I will have that spliced to its correct SC body plug location. I also added a TE2 wire to the ECU connector at Pin #19 that will get spliced together with the Diagnostic Port TE2 wire and SC IK1-2.

I also found the OBD2 O2 sensor ground exactly where that thread above said it should be (for an OBD2 MKIV TT). I removed that. Haven't checked the wire to the O2 sensor connector yet or taped off the loose wire wend yet. I think I may just leave it on the harness.

There was also a wire on one of the MKIV ECU connectors that I had to take from one pin that only applies to OBD2 and insert it into a pin location that only applies to OBD1. Serial communication wire, I think. The pin I took that wire from is as you'd expect only used for an OBD2 ECU and not for an OBD1 ECU. The thread above describes that procedure also.

......

I did end up taking the original thick gauge (14ga?) B+ fuel pump wire from the scrap SC300 harness and I routed that through the chassis grommet of my MKIV connector. The wire is very long but it does have factory splice crimps in a couple of places. I think I will seal those off with electrical tape and further find another way to insulate them. They are factory crimp connections and very solid so I am reluctant to cut them and re-solder this very thick wire any more than will be necessary.

Or... I could just use the wire as a reference and locate some fresh 14 gauge stranded wire. Honestly it looks MUCH thicker than what I'm used to 14 gauge wire looking like. It came straight from the SC IJ1-12 connection which uses a BIG spade.

.....

I took out a long length of brown wire in similar gauge for the Ambient Temp Sensor which has a factory crimp splice. That will be used for Lexus II1-1 along with the A/C Lock Sensor from MKIV II1-20. The long section of that brown wire I will run through the upper plastic cover of the MKIV harness with a little 3M Super 33+ electrical tape to hold it in place. I believe this factory Toyota wire is 16ga but I am not sure. It does look consistent to the gauge of wire for that connection wire on SC II1.

.....

I removed the SC heater VSV wire with long ends from the SC harness and grafted it into the MKIV harness. Just have to solder those connections into appropriate II1 slots now.

.....

Note: when I followed the instructions to reverse OBD2 wiring to OBD1 there is an ECU pin picture diagram with pin locations but I found this reference to be more consistent:



^^ Note that the above ECU pinout is SPECIFICALLY referencing a 1993.5-1995 USDM Supra TT OBD1 ECU. The pins that are not used for OBD1 are therefore marked with an "X". If you were to look at a similar (but different) visual pinout of a USDM TT OBD2 ECU you would see different unused pins marked with an "X".

.....

Really, the only way I was able to get the right wires and pins so easily was because I purchased an intact spare junk SC300 harness to take the body connectors and other wires from. I thought it would be JUST the body connectors and some wire ends that I would need but being able to take anything I need from a spare SC harness has really come in handy.

OEM Toyota repair wires and replacement connectors are the only exceptions to what I have taken from that harness to convert my MKIV TT harness.

...

Now at the moment I have another minor help request! Gerry?

I have all of these connections to formally put together tomorrow prior to buttoning up the harness with electrical tape and protective shielding, but there is still one connection that I cannot find or figure out how to recreate:

For Lexus SC II1-2 (Pin #2), one wire connects to the Red/Blue Heater VSV wire but the same II1-2 pin also gets spliced into "PWR for A/C ECU"... or that "PWR for A/C ECU" wire also gets spliced into Lexus SC IJ1-2 as "Ignition PWR to A/C ECU"...?

1) I can't find any reference to where this "PWR for A/C ECU" originates from on the MKIV harness
2) I can't tell if this connection is supposed to go into SC II1-2 or SC IJ1-2

This is probably one of the more simple wiring connections but for the life of me I'm stumped on that one

gerrb

iTrader: (34)

1) you won't find it on your MKIV harness ... SC has different AC control assembly than the MKIV. That SC IJ1-2 which gets power (IG) from the 10A HTR fuse ... and provides power to that heater valve and SC HVAC control . For the MKIV , the AC assembly gets power (IG) from the 7.5A HTR Fuse through connector IF1 pin 10 .

2) It is indeed connected to IJ1-2 (SC plug)

KahnBB6

iTrader: (5)

Okay, got it! Now does this need to be a particularly thick wire to SC plug IJ1-2? I believe that connection originally had a common factory 16ga wire but perhaps since it is a power connection I need to use one that is a bit thicker?

Also, if the connection for this is not present on the MKIV harness then it stands to reason that a wire and plug for this is present on all SC300 harnesses, correct? I should be able to find a factory connector on my spare SC harness to connect right into the 10A HTR fuse?

If not, I'll just do a splice but it occurred to me this morning that there must be a factory plug on the SC harness for this that I just need to identify and trace.

gerrb

iTrader: (34)

16ga works

yes , it is present in all SC300 harness to power the heater valve and HVAC Assembly

the wire is Pin 2 on the white 12 pin body plug (II1) - that wire is spliced to the heater valve and to IJ1-2 (where it gets its power)

KahnBB6

iTrader: (5)

Okay, thank you! I have the Heater VSV connector/wire grafted into my MKIV harness with the yellow/black wire for SC II1-7 and the Red/Blue-Stripe wire for SC II1-2. That same Red-With-Blue Stripe Heater VSV wire also has a factory splice into another same-colored wire which I assume was for the "PWR for A/C ECU" that goes to the 10A HTR fuse. So I can just repair that factory splice as long as I can connect it to the fuse.

I did some research and found the 10A HTR fuse under the fuse kick panel above the driver's side footwell in the SC300. Should I just wire it directly into that location with a patch-style 10-Amp fuse? Or is there yet a way to run a second long wire from SC II1-2 through the MKIV harness into the engine bay to connect to some factory port (in the engine bay) for 10A HTR?

Looking at the main fuse box under the SC300's hood I did not see any fuse labeled 10A HTR so it appears that the driver's side fuse kick panel is the only connection point for this.

.....

It seems that the only custom under hood wires will be for the Ambient Temp Sensor from SC EB1-7 to SC II1-1, Theft Horn wire to SC IJ1-9 and the big 14-gauge (or thicker) wire to SC IJ1-12. And the MSD Tach Convertor unit.

gerrb

iTrader: (34)

you don't need to run any wire to the 10A HTR fuse .... as long as you have a pin / wire on pin 2 of IJ1 ... then you are already connected to the 10A HTR fuse . That pin 2 of IJ1 wire is spliced with wire 2 of the heater valve connector and pin 2 of II1 (those 3 are connected to each other )