Fuse box question. - 2.7i Build

[kid325e]

I'm getting ready to swap in my 2.7i M20 into my 87 325e. The old engine harness is out already but I'm leaving the fusebox in for the time being, as well at the power junction connections, etc.

My question is, when I install the harness from a 1988 325iX into the engine bay, do i also swap in the fusebox from the same car? Or do you just move around a few pins in the connector on the fuse box side? I apologize if this has been covered but i've been out in the garage all weekend and this question has me stumped.

Any help or knowledge is greatly appreciated. Thanks for your time and Happy Memorial Day Weekend!

Paolo

[jlevie]

The things that need attention are:

The DME START, tachometer, and econometer signals. On your 87 those are via a three pin connector near the DME connector. On the 88 harness those signals go through C101.

Pin 20 of the 87's C101 connector may grounded, which will burn up your engine harness. Clip the wire to pin 20 on the body side of C101.

An 88 or later has an additional wire that connects to the unloader switch in the starter. Unless that wire is grounded the windows, power mirrors, and HVAC blower may not work.

The is nothing that needs to be done to the fuse box.

[Chriskbmx]

see this is slightly confusing to me because my buddy has an 87 dropped his engine right in and didn't have to do any wiring, but from what your saying is that the tach, dme signal, and econ signal is already taking care of by the 87 body harness near the ecu and is not an issue? so all i need to do is clip the wire that goes to pin 20? what does pin 20 control? what is this extra wire that you speak of? is it on the engine harness for the b25 and just needs to be grounded?

[kid325e]

It sounds like all you need to do is clip the wire for pin 20 on the body side of the C101.

Than somehow figure out how to get the connectors for DME Start, TACH, and Econometer lengthened and splice either via the C101 connector or just making the connection.

Or are you just saying clip the wire for Pin 20 on the body side of the C101 connector in my 87 Coupe and all is good? Sorry if i'm thinking too much!

[kid325e]

After re-reading this is sounds like the 1.3 Harness pretty much makes those three pin connector on the 1.1 Harness obselete right? No need to figure out new inputs for DME Start, Tach, and Econometer because those are built into the new 1.3 C101 Connector correct?

So just cut the Pin 20 wire on the BODY side of the C101 Connector and everything should work A OKAY?! Thanks for the info JLEVIE, I know you know your shit!

[kid325e]

I went out and verified that Pin 20 on the body side of the C101 Connector is definitely a Brown Wire (Ground). So that wire will get snipped and capped off with heat shrink..


Hopefully i'm on the right track.

[Chriskbmx]

my cars an 09/86 i wonder if its the same case of snipping just the ground?

[kid325e]

My research shows that if your car is early (No newer than late 87, but check the wire color in Pin 20 on the Body Side to be sure.) and the the wire coming out of Pin 20 on the Body Side of the C101 Connector is Brown/Ground you cut it and cap it off from grounding out, etc.

Just waiting for someone knowledgable to confirm this.

[jlevie]

After re-reading this is sounds like the 1.3 Harness pretty much makes those three pin connector on the 1.1 Harness obselete right? No need to figure out new inputs for DME Start, Tach, and Econometer because those are built into the new 1.3 C101 Connector correct?

While those signals are routed to C101 in an M20 harnesses after 9/87, your car has those signals routed to the three pin connector rather than to C101. So you either have to re-route those to C101 or graft in the 3 pin connector to the engine harness.

So just cut the Pin 20 wire on the BODY side of the C101 Connector and everything should work A OKAY?! Thanks for the info JLEVIE, I know you know your shit!

The body side wire to pin 20 of C101 is a different matter. You cut it so as to not short and burn out the later engine harness.

[Chriskbmx]

so if you use an engine harness from an 87' 325i there will be no issues, because i have no idea what i would do with the 3 prong plug you are tlking about, would it be hard to just cut it and run 3 new pins to the body side c101 for it to match up to the harness? and what pins would these wires have to go to on the body side plug?

[jlevie]

so if you use an engine harness from an 87' 325i there will be no issues, because i have no idea what i would do with the 3 prong plug you are tlking about, would it be hard to just cut it and run 3 new pins to the body side c101 for it to match up to the harness? and what pins would these wires have to go to on the body side plug?

An 87 engine harness has the connector (C104), so it is plug-n-play with respect to those wires.

There are two solutions to the problem. One is to extend those wires and add them to C101, the other is to splice the connector from the old harness into the new engine harness. I'm of the opinion that the latter procedure is the easiest, though adding them to C101 is the most correct method.

[Chriskbmx]

i wonder how hard it would be to add them to the c101 or what your saying is to find those respective wires at the engine side of the c101 cut them and splice them directly to the 3 wires you mentioned earlier? with an 87 harness is there an issue the unloader relay still or no?

[jlevie]

There won't be a problem with the unloader when using an 87 harness.

Adding the wires to C101 isn't easy, but it can be done. You will have to source the pins from BMW. The advantage of adding them to C101 is that you can then use any M20B25 engine harness from 9/87 on without modification.

[Chriskbmx]

i looked and on my body side i have nothing at pin 20?

[jlevie]

i looked and on my body side i have nothing at pin 20?

in that case nothing needs to be done to C101.