85 That Loves to run doesn't love to turn off

[Goodman90]

Hi there,

I just joined the forum but I have been using it for awhile now to troubleshoot problems. But this one is driving me crazy so i had to ask for help.

I have a 85 CJ7 with the i6 all pretty much bone stock, when I bought it though the wiring under the dash was horrible. I had my buddy who is an E-Tech look at it and he was stumped as to what they P.O was thinking when wiring this thing. So i bought an American AutoWire wiring harness and started to rewire.

When i left for work 2 weeks ago i had finished the dash and the engine compartment and everything was working fine. Turned on, ran better than when I had bought it. Came home last night to a dead battery. Which I figured I probably left a light on or something. I jumped it let it run for awhile now it wont shut off when I turn the key to the off position. Any ideas??

The thing that puzzles me is that it worked fine when I left, It rained a lot while i was gone but the jeep is in a garage and when I was wiring i soldered everything and used shrink wrap so I really don't think it is because of the humidity

 

[Lumpy Grits]

:ww:
I would look for a 'back-feed' from your alternator.
Disconnect the alt. With a fully charged battery, start'er up. Now, if you can turn the engine off with the key. You know where to look.
I use a diode in the 'excite' wire of the alternator because my MSD ign box will cause, what you are seeing.
LG

 

[gert]

:ww:

I would look for a 'back-feed' from your alternator.

Disconnect the alt. With a fully charged battery, start'er up. Now, if you can turn the engine off with the key. You know where to look.

I use a diode in the 'excite' wire of the alternator because my MSD ign box will cause, what you are seeing.

LG

Same here, I had to put a diode on my alternator to be able to make mine turn off


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[Torxhead]

So Lumpy and Gert, are you both talking about the wire between the alternator #2 post and the connection that goes to the positive side of the coil? This would replace the 15 ohm(I believe it is) resistance wire that was an oem item to stop the "backfeeding" from the alternator. Doesn't that diode have to be facing a certain way also?

 

[gert]

So Lumpy and Gert, are you both talking about the wire between the alternator #2 post and the connection that goes to the positive side of the coil? This would replace the 15 ohm(I believe it is) resistance wire that was an oem item to stop the "backfeeding" from the alternator. Doesn't that diode have to be facing a certain way also?

Yes that is the one, I thinned out my harness when I bought it to get ride of the computer and it wouldn't turn off so I had to add the diode in that wire


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[Goodman90]

Thanks for the help. It starts without the alternator and stops, so now I have to find where it is backfeeding.

What is this diode solution? Kinda seems like it will fix the problem but not the actual problem, which I am fine with. But just wondering why it would work then all of a sudden stop.

 

[Lumpy Grits]

See page #8.
http://documents.msdperformance.com/6425.pdf

LG

 

[gert]

Yep there you go I couldn't remember if I had added mine when I did the msd swap or not


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[Lumpy Grits]

So Lumpy and Gert, are you both talking about the wire between the alternator #2 post and the connection that goes to the positive side of the coil? This would replace the 15 ohm(I believe it is) resistance wire that was an oem item to stop the "backfeeding" from the alternator. Doesn't that diode have to be facing a certain way also?

The 'band' on the diode is toward the alt.
I do not recall the rating of the diode that came in the MSD kit. Mine is covered in heat- shrink now. You can call MSD for info.
Be VERY cautious if you solder the diode. Use a heat sink to keep it cool while soldering.
LG

 

[Goodman90]

Awesome info!

Thanks once again fellas, I"m going to give it a shot first thing tomorrow. Hopefully this will fix it up.

 

[Torxhead]

From info that I have gathered years ago, the diode would be a Radio Shack p/n 276-1143. This would apply to the Motorcraft ignition used in CJs from '78-'86.