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Ecu harness though the firewall


socalsean

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I just received my Megasquirt and need to pass the harness though the firewall on the passenger side. Where have you guys hole sawed? I'm not apposed to using a bulkhead connector, but I'd like to drill the hole in an ideal spot. Photos would be awesome! Thanks!

 

sean

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How big does the hole need to be?

 

There is a hole on the passenger side that I believe is for an AC hose, which I enlarged to be able to slip an O2 sensor through when I was installing an AFR gauge.  I had to cut through the firewall insulation on both sides, but that was not difficult.  You do have to watch out for the brake lines.

021.thumb.JPG.4fb84ef0356dfbcdecb1915e1672ff78.JPG

That flat piece with green on it was the factory plug for the hole.  The foam doughnut is the inner sound proofing stuff.025.thumb.JPG.d287e2e4ed3551ad15493a47bc0ddec4.JPG029.thumb.JPG.47cd9bcd21b34870c3d03a766abe2a4d.JPG

 

I enlarged that hole with the tapered reamer and then made a rubber grommet to protect the wires, since there were so many sharp edges inside.

013.thumb.JPG.e5af94fb5a36e3e57faf4556f817c825.JPG028.thumb.JPG.7715e3eaade4ccc6733cb4282e115e16.JPG030.thumb.JPG.d12fc47ca556c48e60fc4b1512172646.JPG038.thumb.JPG.0990a4c19fbce287e181194b3f813ab0.JPG040.thumb.JPG.810062b5603b21aa9f4b30eeb1da8029.JPG055.thumb.JPG.77e4f440b04c79b5de9f13b91a60a51b.JPG

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     DISCLAIMER -- I now disagree with much of the timing advice I have given in the past.  I misinterpreted the distributor curves in the Blue Book as timing maps for our engines.  I've also switched from using ported-vacuum to manifold, with better results.  I apologize for adding confusion.  (3-28-2024)  

 

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5 hours ago, '76mintgrün'02 said:

How big does the hole need to be?

 

There is a hole on the passenger side that I believe is for an AC hose, which I enlarged to be able to slip an O2 sensor through when I was installing an AFR gauge.  I had to cut through the firewall insulation on both sides, but that was not difficult.  You do have to watch out for the brake lines.

021.thumb.JPG.4fb84ef0356dfbcdecb1915e1672ff78.JPG

That flat piece with green on it was the factory plug for the hole.  The foam doughnut is the inner sound proofing stuff.025.thumb.JPG.d287e2e4ed3551ad15493a47bc0ddec4.JPG029.thumb.JPG.47cd9bcd21b34870c3d03a766abe2a4d.JPG

 

I enlarged that hole with the tapered reamer and then made a rubber grommet to protect the wires, since there were so many sharp edges inside.

013.thumb.JPG.e5af94fb5a36e3e57faf4556f817c825.JPG028.thumb.JPG.7715e3eaade4ccc6733cb4282e115e16.JPG030.thumb.JPG.d12fc47ca556c48e60fc4b1512172646.JPG038.thumb.JPG.0990a4c19fbce287e181194b3f813ab0.JPG040.thumb.JPG.810062b5603b21aa9f4b30eeb1da8029.JPG055.thumb.JPG.77e4f440b04c79b5de9f13b91a60a51b.JPG

 

Beautifully-done, of course, Tom, but its original purpose is not clear to me...yet. Holes in the firewall for A/C lines were strictly post-factory, always in pairs (supply and return line), and 1 1/4” in diameter.

 

I have some vague recollection of a thread that identified a more likely purpose for this extra hole — could it relate to RHD cars, perhaps.... ?

 

Best regards,

 

Steve

 

1976 2002 Polaris, 2742541 (original owner)

1973 2002tii Inka, 2762757 (not-the-original owner)

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58 minutes ago, Conserv said:

 

Beautifully-done, of course, Tom, but its original purpose is not clear to me...yet. Holes in the firewall for A/C lines were strictly post-factory, always in pairs (supply and return line), and 1 1/4” in diameter.

 

I have some vague recollection of a thread that identified a more likely purpose for this extra hole — could it relate to RHD cars, perhaps.... ?

 

Best regards,

 

Steve

 

Believe that thread revealed it was for the speedometer cable on RHD cars. I've been known to be wrong occasionally.

Jim Gerock

 

Riviera 69 2002 built 5/30/69 "Oscar"

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1 hour ago, jgerock said:

Believe that thread revealed it was for the speedometer cable on RHD cars. I've been known to be wrong occasionally.

 

Thanks, Jim. That’s excellent!

 

And I think your “wrong occasionally’s”, Jim, are preferable to my “vague recollections”.... ?

 

Best regards, 

 

Steve

 

Edited by Conserv

1976 2002 Polaris, 2742541 (original owner)

1973 2002tii Inka, 2762757 (not-the-original owner)

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I'm redoing the wiring harness in my car and relocating the fuse box inside.

 

I bought one of these to do it:

https://www.amazon.com/Position-Delphi-Weather-Connector-Locks/dp/B00EZSHYVQ

 

The only catch is that it's pretty large, requiring a 2" hole + space for the mounting studs.  I'm going to try and fit it in the spot where the two wire bundles currently come through the firewall, but it will be tight.

 

I bought a second connector for when I go EFI, but I don't know where I'd run it.  There's a lot of room on the passenger side, but I'd like to keep that area clean and run the wires close to the main bundle if possible.

John Baas

1976 BMW 2002

2001 BMW M5

My Blog!

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1 hour ago, xr4tic said:

I bought a second connector for when I go EFI, but I don't know where I'd run it. 

Count the wires, two may be needed.  Mounted just below the "ledge" on the firewall.  Not exactly happy with the mess and there must be better bulkhead connectors around, like rectangular.  Allow for future additions and/or a change of ECUs.  Circuits here include crank and cam sensors, coil per plug ignition, fan control besides the std fueling and power all thru the connectors.  ECU shown has been superceded.

Bulkhead Conn Inside 02.JPG

Bulkhead Conn Outside 01.JPG

Edited by jimk

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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I've been eyeing a spot that is a mirror image location to the grommet where the hood release cable goes.  If you drill a hole there and protect it with a grommet, the cables will enter that pocket where the fender meets the firewall.  There is an oval hole in the side that will allow the wires to emerge into the engine compartment.  it is high up enough that the harness will not be subjected to exhaust heat.

 

I think the stock ignition coil is mounted right over that oval hole.

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30 minutes ago, Healey3000 said:

There is an oval hole in the side that will allow the wires to emerge into the engine compartment.

I have the E30 battery cable routed to a spot in the firewall and it exits thru that hole.  It can be seen from the engine side in the last photo above.  I used the E30 firewall grommet for the firewall.

The finished inside the car is not too messy.

Final Carpet.JPG

Edited by jimk

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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1 hour ago, jimk said:

Count the wires, two may be needed.  Mounted just below the "ledge" on the firewall.  Not exactly happy with the mess and there must be better bulkhead connectors around, like rectangular.  Allow for future additions and/or a change of ECUs.  Circuits here include crank and cam sensors, coil per plug ignition, fan control besides the std fueling and power all thru the connectors.  ECU shown has been superceded.

 

I'll most likely run a simple Megasquirt setup, I think I can fit it into 22 pins.

 

I looked into the mil-spec connector option, which can fit more into a smaller space, but it's $250 for that connector + the expensive crimper it requires.

https://www.milspecwiring.com/41-WAY-1620AWG-MILSPEC-KIT-3470_p_1596.html

 

 

John Baas

1976 BMW 2002

2001 BMW M5

My Blog!

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  • 2 months later...

Depending on how many wires and the size of the loom, you can run it through the hole on the right side through the (mirror image) passage for the wiring harness. It comes out the opening just near the coil as the wiring harness does on the left hand side.

 

No drilling.

 

I run the wire harness for the Lambda sensor as well as the wires for the J&S through there, though with a large connector, it won't have room; if you can snake the wires without the connector then reattach it should work.

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Many more selections now than 10 years ago when I installed a bulkhead connector.  But pick one that you can add/change circuits to easily.  The system you pick will not be static nor the last one.  

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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