Wiring up MJLJ. What wire ratings do I need

MrSandman · Post by **MrSandman** » Mon Feb 20, 2006 9:35 pm

I am ready to start wiring in my MJLJ but am unsure of what core wire to use.

I have sourced some shielded wire from a local electronics supplier but this is only rated at 1 amp max. Will this be OK for the VR feed and SAW, PIP connections.

What do I need for the other wires. Will 5 amp suffice for all connections or do the 12v EDIS feed and the coilpack connections require more than 5 amps.

Also the wiring diagram does not show any fuses. I am guessing that it would be wise to fuse the MJLJ but how about the EDIS, and what ratings.

I have searched the forums but cannot find the question asked elsewhere.

Any advise would be appreciated as I don't fancy frying my board but am not that keen on an electrical fire on the way to Le Mans either.

Thanks,

Steve

Oliver Sedlacek · Post by **Oliver Sedlacek** » Tue Feb 21, 2006 11:21 am

1 amp is fine for sensor signals (i.e. VR), SAW, PIP, Megajolt supply, rev counter and EDIS supply. I would use something rated at 10A for the coil pack connections and the grounds. I run my system without a fuse.

MartinM · Post by **MartinM** » Tue Feb 21, 2006 11:48 am

I think the clues to your questions are in the way that Ford designed the EDIS wiring harness. After all, if it's good enough for them...

When you say 1 amp shielded I presume you mean one core with a shield?

So...
...shielded for VR sensor - I *think* the shield isn't grounded by the way - and your 1 amp shielded will be fine
...something similar to the tails you've probably got on your EDIS connector - 5 amp will be fine.

Interestingly, Ford didn't shield the PIP and SAW signal wires, either from each other or the coil driver lines.

Please use a fuse to protect the MJLJ, EDIS and all your bespoke wiring - 5A will be fine. There are many failure modes inside the MJLJ and your bespoke wiring that could short the incoming +12v to earth, and without a fuse you will get a lot of smoke (and the thicker the wire you use, the more smoke) and/or a fire. Which is a Bad Thing (TM).

ckenyon · Post by **ckenyon** » Tue Feb 21, 2006 2:47 pm

The pip/saw lines are run with the IGN GND signal return line in the ford installation, all of these are shielded and the shield is also connected to the VR line shield in the ford installation. Reference a Ford Explorer 1990 - 2000 shop manual.

ckenyon · Post by **ckenyon** » Wed Mar 01, 2006 5:44 pm

I just bench topped my whole system. I had grounded the pip/saw shield, this resulted in tach and advance instability. As soon as I disconnected the shield to ground connection, everything was rock steady. My lesson, the pip/saw shield and the VR sensor shield should be connected together and connected to the edis module only, just like the OEM installation.

JamesC · Post by **JamesC** » Sat Jul 08, 2006 12:12 am

So to get this right - the wiring diagram that is on this site is wrong?

The shields go to pin 7 on the EDIS - and that is it? EDIS is grounded via pin 9.

The diagram on the site shows that the shields go to EDIS pin 7 and also to ground.

MartinM · Post by **MartinM** » Sun Jul 09, 2006 1:14 pm

Which diagram?

JamesC · Post by **JamesC** » Sun Jul 09, 2006 3:41 pm

This one:

http://picasso.org/mjlj/?q=node/606

PIP/SAW and VR shields are connected to pin 7 - which is connected directly to the ground.

MartinM · Post by **MartinM** » Sun Jul 09, 2006 7:13 pm

Well it's wrong according to the three EDIS connectors I've just looked at - the shields of the VRS cable and the PIP/SAW cable are connected to each other and pin 7 of the EDIS only.

Another slight complexity on the real connectors I've got is that the PIP/SAW cable is three conductors plus a shield - one is the PIP signal (EDIS pin 1), one is the SAW signal (EDIS pin 3), one is the "IGN GROUND (signal return)" (*) (EDIS pin 4) and then the shield (EDIS pin 7). I've not seen any diagram (not to say there isn't one somewhere) that shows connecting EDIS pin 4/IGN GROUND to anything

(*) - from http://www.dainst.com/info/edis/edis.html

JamesC · Post by **JamesC** » Sun Jul 09, 2006 8:13 pm

Cheers for the clarification Martin.

I was browsing around and found the EDIS wiring diagrams - noticed that there was no ground on that wire.

Someone should really get that diagram changed as it's on the main install page!

davepsmith · Post by **davepsmith** » Tue Jul 11, 2006 12:32 pm

Martin
I am just installing MJ on a pinto. I have made up the wiring harness acording to the wiring diagram. I now have a doubt on the ground.

Effectively I have combined all the grounds, EDIS Pin 7 Pin 9, MJ ground and the VR and PI/SAW shields to the battery negative. Is this a problem?

MartinM · Post by **MartinM** » Tue Jul 11, 2006 1:42 pm

I think that might be too many together. There are reported problems (not from me) when too many grounds connections are made - so people disconnect some of them and it all works much better.

I would suggest:
- At the EDIS module:
...VR and PIP/SAW shields to EDIS pin 7 only (the tails on your EDIS connector should do this)
...EDIS pin 9 to ground
- At the MJLJ unit:
... Gnd (pin

to ground
... do not connect the PIP/SAW shield to anything, but minimise the length of the unshielded PIP and SAW cores to the MJLJ connector
- At the VRS end of VR line:
...just use the two pin connector (I suspect the shield is just left disconnected inside the connector)

So, in summary, ground everything you think you should, EXCEPT for the shields where at the EDIS end they connect to pin 7 only and at the other ends they are not connected to anything

On my install, which works fine:
- the tail on the VRS connector was long enough to rejoin to the VRS tail of the EDIS connector (two cores and the shield)
- I didn't know what to do about the PIP/SAW shield so ignored it and used some thin (unshielded) 2-core mains cable to extend the PIP/SAW cores from the EDIS connector to the MJLJ - about 1.5m of cable IIRC

It ain't broke, so I'm not going back to fix it!!

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