M20 swap; what fuse box do I use?

[hornhospital]

I feel so stupid asking this, but I've read all the M20B25-into 'e' chassis car threads I can find here and elsewhere (including the stickied one at the top of this forum) and cannot figure this out, so don't kill me. I know some of you will be tempted to say "this has been covered a million times". Maybe, but I tried to find it on my own and came up with no solid info. 99% of the swap threads are those going into a post-5/86 build chassis, which has the round c101 socket and larger fuse box....

What I have:

1985 325e chassis complete, just minus the engine and transmission. Still has the original chassis harness. This has the small fuse box and rectangular c101 plug/socket

1988 M20B25 engine with harness, 173 ECU and 5 speed. I have the large fuse box and round port c101 socket, but it's still connected to the chassis harness in the wrecked car the M20B25/5 speed came out of.

I know I'll have to splice a couple wires in the glove box from the c104 connector. I can handle that (I think). It's the rectangular port c101 to round port c101 I'm confused about.

I understand I'll need to splice the round plug socket to the wires from the rectangular c101 connector coming from the fuse box so the 'i' engine harness will plug up. Do I use the 1985 fuse box and chassis harness, or does the 1988 fuse box with the chassis harness need to be transplanted (please say no....I can't imagine removing all that dash wiring and swapping it )

If I cut and splice, what stays in the '85, what gets swapped, what gets cut/spliced, and exactly where do I cut/splice?

By the way, the entire rest of the engine swap is done. Everything is in and connected except the wiring harness-to-fuse box/chassis harness connections. :thankyou: in advance!

[bluebeamer]

Give this a read if you already havent, might help you out

http://www.e30zone.net/e30zonewiki/index.php/C101

[modernist]

Get yourself some electrical troubleshooting manuals. Linky

[hornhospital]

Thanks guys, but I already had both the ETMs and the pinout comparisons between the rectangular c101 and round c101. What I need to know is do I keep the 85 fuse box and splice the round c101 socket in place of the rectangular one, or do I have to swap the 88 fuse box in?

[barry]

Google this subject I just replaced my fuse box on my 88 325is it was not that hard. if you need a fuse box I have one off a 88 325i

All a fuse box does is route your wires by using fuses and relays

[modernist]

You don't need a new fuse box.

[hornhospital]

Google this subject I just replaced my fuse box on my 88 325is it was not that hard. if you need a fuse box I have one off a 88 325i

All a fuse box does is route your wires by using fuses and relays

I did Google it. Conflicting information all over the place. That's why I'm here. To get the best info from those who have actually done what I'm doing.

Thanks, but I have the fuse box (and the whole dash/chassis harness) from the wrecked 88.

You don't need a new fuse box.

THAT'S what I needed to know. Thank you!

[TobyB]

You don't NEED a new fusebox. A few splices, and you're good to go. Make sure
that pin 20 isn't red on one side and green on the other- that melts things.

However, what I found when I combined an 87 chassis to a 91 engine was that
I SHOULD HAVE wired the car as a 91. I now have a half- n- half, and it
takes a little decoding to figure out what is what where. Had I swapped the entire
box and everything from the 91, it would have BEEN a 91 for electrical purposes,
and that much less confusing 10 years from now.

That all said, mine's a race car I completely stripped, so swapping the whole harness
would not have been all that hard.
You'd have to pull the dash to do the swap (not all that hard, but time- consuming)
and getting wiring under the carpet, etc...

t

[hornhospital]

Thanks, Toby! I'll remember that. Mine's a bit different than most. Motronic engjne harness into an L-Jetronic chassis harness. It's been a head-scratcher for a few days.

[beancent]

fuse box swapp not needed

You do not need to swap fuse boxes. I have an 85e like yours and all i did was cut the 85 engine harness just before the rectangular harness pulled the engine harness rectangular plug off with about 6 inches of wires left on it and spliced that into the cut off round plug and harness wires from your 88, give yourself enough length on the wires from each cut off harness to plug everything back together. Splice your wires according to the link posted in the above previous post, and you end up with two plugs. You will end up with some extra wires in the 88 harness that will not be needed just tape the ends up.

[hornhospital]

Thanks for the confirmation. That's exactly what I've done, but haven't spliced the wires yet. Weather got nasty here right after I cut the harness.