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JBD's Project CQ - Merging the 7A & 3B Harnesses

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 Post subject: Re: JBD's Project CQ - Starting on the 3B Swap...
PostPosted: Thu Jan 14, 2021 9:43 am 
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yodasfro wrote:
That's for the 7A sub harness, MFTS coolant temp sensor and oil pressure switches.


Thanks Austin!

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sun Jan 17, 2021 9:20 pm 
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So, that sub harness feeds those signals to the Autocheck system, right? If so, it seems I won’t need them on the 7A harness since the 3B harness has those same connections and I have the spreadsheet (BostonCQ’s) that shows where to tie those in to the 7A Autocheck.


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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sun Jan 17, 2021 9:30 pm 
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mostly aux gauges

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Tue Jan 19, 2021 4:35 pm 
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Swimming in wiring diagrams and harnesses, but I think I have a handle on everything needed to run the engine. Things that are still left to figure out 100% are as follows.

1) carbon canister/evap. I don’t see where the 3B controls the second valve (shut off) like the 7A has.

2) AC wiring. I think I have this one figured out, but not sure if the manual HVAC swap is going to throw a wrench in things.

3) 3 stage cooling fan. I think I just need to dust off the wiring plans I’ve found over the years and figure out how to use the OEM UrS resistor pack I have.

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Tue Jan 19, 2021 8:35 pm 
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Hey Brent! I have the fan resistor packs from both the 200’s if you want them. Maybe next week some time we can meet somewhere if it’ll help you out. I can’t drive until Monday, recovering from foot surgery.

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Tue Jan 19, 2021 10:03 pm 
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1) carbon canister/evap. I don’t see where the 3B controls the second valve (shut off) like the 7A has.

only one N80, blue connector

3) 3 stage cooling fan (i assume you want to use 500 watts fan, if not, dont change anything
E1, E2 in, E3 out (use E1 for low speed, after run, use E2 for mid speed, direct 12+ for high speed)


Attachment:
respack.jpg
respack.jpg [ 21.92 KiB | Viewed 349 times ]

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Wed Jan 20, 2021 6:20 am 
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czd3my wrote:
Hey Brent! I have the fan resistor packs from both the 200’s if you want them. Maybe next week some time we can meet somewhere if it’ll help you out. I can’t drive until Monday, recovering from foot surgery.


Hey Chuck! I have a brand new resistor pack that should do the trick, but I really appreciate the offer. I wouldn't mind a spare though. Don't make a special trip for me, but next time either of us head in the other's direction, maybe we can meet up then.

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Wed Jan 20, 2021 6:39 am 
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varia wrote:
1) carbon canister/evap. I don’t see where the 3B controls the second valve (shut off) like the 7A has.

only one N80, blue connector

3) 3 stage cooling fan (i assume you want to use 500 watts fan, if not, dont change anything
E1, E2 in, E3 out (use E1 for low speed, after run, use E2 for mid speed, direct 12+ for high speed)


Attachment:
respack.jpg


So, it'll be okay to leave the N115 (carbon canister shut-off valve) unplugged? Or do I need to convert to a 3B carbon canister setup?

Yes, I have a 500w fan and an RS2 fan shroud. That's what i was planning...going off this wiring diagram I found.

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Wed Jan 20, 2021 8:19 am 
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yes it good for guidance, but select decent connectors, wire gauge, relays cos that thing pulls over 50A when starts and 40A when running.

you can leave the carbon canister out if you want, you can use b4 in the fender. i never used the b3

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 Post subject: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Thu Jan 21, 2021 6:14 am 
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I think I’m ready to start soldering. I was in the garage last night mocking up the two harnesses. What’s left of the 7A harness is on the left and will go through the original firewall hole. On the right, is the 3B harness that will go through a new 2.5” hole in the firewall near the AC lines. I’m going to try and tuck the ECU in the same spot as the 7A ECU, but there’s a lot more lead between the firewall grommet and the ECU plug. So, we’ll see.

Based on my time spent with the wiring diagrams, most (but not all) of the splicing occurs between the wires circled in red. Exceptions are for the AC, after run, and 500w fan circuits.

It’s hard to tell if I’m going to have too much wire or not enough wire for each of the connections to be made. In most cases, I think it’s the former. I suppose I could do the soldering in the car, but that doesn’t sound comfortable. Any tips on this or the rest of my plan would be appreciated.

I made this document while reading the wiring diagrams to use as a guide for the merge effort. Please let me know if you see any issues with it. Hopefully it will be useful to others.

https://drive.google.com/file/d/1kBweR2 ... sp=sharing

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Fri Jan 29, 2021 3:45 pm 
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Splicing on the wiring harness is almost done. I decided to invest in a ratcheting open barrel crimper and have been pleased with it so far.

I have a manual HVAC swap question for to folks.

There’s a wire from the 7A MFTS to the climate control head that tells the system it’s okay to run the compressor. It prevents the AC compressor from coming on in an overheat scenario. Does anyone know where that wire goes for the manual HVAC?

This signal also goes to the 3B ECU, pin 36. I’m thinking it needs to go to the AC clutch relay, but not sure which terminal. If anyone has a wiring diagram for a B4 cabriolet manual HVAC, I should be able to figure it out.


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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sat Jan 30, 2021 4:43 pm 
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Worked on the battery relocation today. Just mocking it up in the engine bay because I will need to do some painting. I plan on running an Odyssey PC925 with the following:

  • Negative 2/0 to gas tank bolt
  • Negative 2/0 from passenger front frame rail (procon-10 bolt location) to transmission
  • Positive 2/0 from battery to 200 amp breaker
  • Positive 2/0 from breaker to battery terminal at firewall
    * Positive stock cable from firewall terminal to starter
    * Positive stock cable (from 7A harness) from firewall terminal to fuse panel
    * Positive from firewall terminal to headlight relays
    * Positive from firewall terminal to 70 amp high speed fan relay

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Last edited by jbrentd on Mon Feb 01, 2021 12:45 pm, edited 1 time in total.

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sun Jan 31, 2021 11:56 am 
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I got something like that for my firewall battery cable pass through.

https://www.amazon.com/Bulkhead-Battery ... B075FGQP1Z

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sun Jan 31, 2021 1:07 pm 
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ralleyquattro wrote:
I got something like that for my firewall battery cable pass through.

https://www.amazon.com/Bulkhead-Battery ... B075FGQP1Z" onclick="window.open(this.href);return false;
In hindsight, that would definitely be cleaner, since you wouldn’t need any of the cable in the engine bay.


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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sun Jan 31, 2021 7:51 pm 
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jbrentd wrote:
Splicing on the wiring harness is almost done. I decided to invest in a ratcheting open barrel crimper and have been pleased with it so far.

I have a manual HVAC swap question for to folks.

There’s a wire from the 7A MFTS to the climate control head that tells the system it’s okay to run the compressor. It prevents the AC compressor from coming on in an overheat scenario. Does anyone know where that wire goes for the manual HVAC?

This signal also goes to the 3B ECU, pin 36. I’m thinking it needs to go to the AC clutch relay, but not sure which terminal. If anyone has a wiring diagram for a B4 cabriolet manual HVAC, I should be able to figure it out.


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To follow up on this...

I did some testing on the MFTS and the 2/R terminal (the one that goes to the AC clutch relay) is a normally open circuit. In other words, it doesn’t send the signal until the temp is high. Although not ideal, I’ll probably roll without that signal. That’ll mean my AC won’t shutoff automatically in an overheat scenario.


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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Mon Feb 01, 2021 5:21 am 
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Looks like that signal goes to terminal 13 of the AC Clutch control module.

https://12v.org/urs/1996_Audi_Cabriolet_System_Wiring_Diagrams.pdf

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Mon Feb 01, 2021 6:22 am 
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jonas-k wrote:
Looks like that signal goes to terminal 13 of the AC Clutch control module.

https://12v.org/urs/1996_Audi_Cabriolet_System_Wiring_Diagrams.pdf


Thank you! So, if I'm not mistaken, the B4 cabriolet's AC clutch control module/relay (aux panel positions 3 & 4) is different from the B3 AC relay (aux panel position 4).

This shows what you confirmed...that the MFTS 2/R wire goes to terminal 13 on the AC clutch control module.

Image

And for the B3, the MFTS 2/R wire goes to the AC control head. From here, I assume it goes to the AC programmer and then to the AC clutch control relay (terminal 5/T).

Image

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Mon Feb 01, 2021 3:45 pm 
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jbrentd wrote:
Thank you! So, if I'm not mistaken, the B4 cabriolet's AC clutch control module/relay (aux panel positions 3 & 4) is different from the B3 AC relay (aux panel position 4).

That's how I'm reading it, but I'm no expert.

jbrentd wrote:
And for the B3, the MFTS 2/R wire goes to the AC control head. From here, I assume it goes to the AC programmer and then to the AC clutch control relay (terminal 5/T).

Makes sense. What's missing from much of the Bentley is an explanation for how it all works together. But I guess from a repair perspective that isn't really needed.

Also, I really enjoy following your build. Very useful for when I did my own 20vt CQ swap this past June. And it keeps giving me reminders for all the things I need to do when next I have the engine out, etc.

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sat Feb 06, 2021 4:14 pm 
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Battery now lives in the trunk. Not sure why, but the idea of relocating the battery used to stress me out. I would over think cable size, relay location, etc.

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sat Feb 06, 2021 5:31 pm 
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Nice, now strap it down.

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sat Feb 06, 2021 5:52 pm 
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varia wrote:
Nice, now strap it down.
Thanks. Yeah, I plan to get one.


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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sat Feb 13, 2021 8:40 pm 
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For the radiator fan wiring you might want to have a peek at this thread with refrence to how I wired mine, Depending on the quality of your fan, The cheaper ones don't do well with the sudden start of a relay switching on.
https://www.motorgeek.com/viewtopic.php?f=5&t=215329
HTH

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sat Feb 13, 2021 9:32 pm 
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rally3 wrote:
For the radiator fan wiring you might want to have a peek at this thread with refrence to how I wired mine, Depending on the quality of your fan, The cheaper ones don't do well with the sudden start of a relay switching on.
https://www.motorgeek.com/viewtopic.php?f=5&t=215329" onclick="window.open(this.href);return false;
HTH
Thanks for that. I do remember seeing that thread.

I plan on driving the 200’s 500w fan via an OEM resistor pack for speeds 1 & 2 and a 70 amp relay, using the original wiring.


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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Sat Feb 13, 2021 9:57 pm 
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you should use a decent wire (like 6 awg) for the high speed fan.

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 Post subject: Re: JBD's Project CQ - Merging the 7A & 3B Harnesses
PostPosted: Mon Feb 15, 2021 8:19 am 
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Just to clarify, I’m using the original wiring as a trigger for the 70amp relay. Using new, heavier gauge wiring for the high speed between the battery/fuse/relay/fan.


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