The Project Pad

I'm doing a 3b swap into a 4K running the stock Motronic ecu and wiring harness. I could use some info from people who have done this. pretty please

A couple of the blaring questions are things like; do I need the Engine Control Power Supply Relay? It seems to me from the wiring diagrams that it is resundent. I have the plug in the harness but don't have the relay.

I basically need some help figuring this out. Thanks a ton

I know it can be done but I have never modified or looked at the 3B harness up close.
Multiple options to go here, but I am assuming you want to retain the stock harness for cost purposes? Only asking because if not EFI express can make you a PNP harness to work with VEMS that will be much cleaner and MUCH less headache,
If you are wanting to do it yourself I would recommend contacting paul @ s2central.
These are the connections I used to tie AAN harness into a B3 coupe listed on this page.
http://www.s2central.net/S2_Schematics/ABY_Wiring.pdf
I am not sure if Paul has a page like this for the 3B but he should have some diagrams.
If you look on bundle 5.1, those are the connections I tied in with my main fusebox, which should tie in right where you are missing a few wires from removing the old 4K stuff. There are 6 or so connections there that will provide the power to your ECU and your fuel pump (only when engine is cranking and >13 RPM IIRC).
You may also need to source a proper fuel pump relay from your parts car to put in place of the stock one
http://www.s2central.net/wiring02.html
http://www.s2central.net/motronic_pinout_3B.html
http://www.s2central.net/motronic_04_fuses_3B.html

^^^Great info here ^^^

Thanks, I am starting to get a pretty good idea now.

Is the AAN and 3B J17 relays the same? The 3b diagram shows two connections that the AAN schematic doesn't show. 50/31 to ground and 49LA that goes to nothing.

The reason I am asking is that I am trying to source a 200 fuel pump relay because the 4000 fuel pump relay has 1 output and I would like the dual outputs for proper installation.

This is my buddies car and we decided to go with the Stock ecu/harness because it fell into our hands and seemed like a challenge.

Anybody have a J17 relay with dual outputs? Not sure if the AAN relay will work although it looks to me that it should.

I used a 3b fuse box with the relays in it. made life much easier.

durq wrote:I used a 3b fuse box with the relays in it. made life much easier.

Did you try using the 4K relay panel?

It went into an '83 Urq. I don't know if the 4k boxes are different. The boxes were different enough that it seemed easier to just use the 200 box. If I remember correctly there was a pin or maybe more that the '83 box didn't have that was needed and the relays were all there and correct for the 3b (I guess that would be obvious). I am sure that the early box could be used because it has been done by others, it was just easier to swap the boxes. I bought a donor car so I had everything I needed. there were some older threads on MG that showed how to do it. PM me your email and I will send you some images that i used. There are some screen grabs which have addresses on them which may help too.

durq wrote:It went into an '83 Urq. I don't know if the 4k boxes are different. The boxes were different enough that it seemed easier to just use the 200 box. If I remember correctly there was a pin or maybe more that the '83 box didn't have that was needed and the relays were all there and correct for the 3b (I guess that would be obvious). I am sure that the early box could be used because it has been done by others, it was just easier to swap the boxes. I bought a donor car so I had everything I needed. there were some older threads on MG that showed how to do it. PM me your email and I will send you some images that i used. There are some screen grabs which have addresses on them which may help too.

assrh19@hotmail.com

Thanks a lot