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DUI Distributor and relayed power supply

18103 Views 20 Replies 7 Participants Last post by  ClarkWGris
Ok, I am a little baffled with this one. My jeep is an 86 CJ-7 and I installed a DUI distributor. Works great, I recommend it. Anyway, to get the full constant voltage to the distributor, I wired in a relay just as described here: Classic Inlines - DUI Distributor Installation

I basically used the main red/white ignition wire going into the ignition module as 12 volt power to activate the relay when the ignition switch comes on. I also ran a 10 guage wire from the battery to the relay to be connected to the distributor when the ignition switch is on and the relay closes. Works great, runs great, just won't cut off when I turn off the ignition switch! I don't get it. The only way I can shut off the jeep is to disconnect that main 10 guage wire from the battery. I need an electrical engineer to help me with this one.

Any suggestions?

This is my relay wiring:

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· Premium Member
11,200 Posts
Where did you get the relay?

Sounds like you have one of two issues...

1. "Latching Relay"
Once a 'Latching Relay' closes, it's self powering and won't open until you break the power feed to the relay.

Latching Relays are fairly rare, but if you salvaged the relay from something else, instead of buying one new (salvage relays are perfectly acceptable, but are sometimes an unknown quantity).

2. You put the relay in without putting a DIODE in the 'Excite' wire to the alternator,
Which is 'Back Feeding' the relay once the engine is running.
The same wire that feeds the ignition coil/module in the factory stock system also excites the alternator in most CJs.

Try unplugging the two wire plug to the alternator, and if your problem goes away, it's the alternator 'Excite' feed that is causing trouble for you.

If your engine shuts down when you turn the key off with the alternator plug loose,
Then it's a simple fix, you will need to drop by Radio Shack and pick up some Diodes,
Radio Shack p/n 276-1443 or 276-1444 and install one (Stripe facing alternator) in the smaller of the two wires feeding the alternator plug.

Here is an example of the diode in the line,


· Premium Member
11,200 Posts
If you are wired according to that diagram, and have a PROPER relay, you don't need a diode. Looks like you have either the wrong relay or a bad one, a diode is no cure for that!
Also, with the DUI distributor you are better off to run a separate relay strictly for the dizzy. That thing can eat alot of juice.

The relay he's running IS FOR THE HEI.

The activation wire for the relay is the old Coil/Module wire, and that wire also feeds the 'Excite' wire to the alternator.
When the alternator starts charging, that wire goes POSITIVE and powers up the relay reguardless if the key switch is on or off.

It will let the current from the ignition switch 'Excite' the alternator,
But it won't let the current from the alternator backfeed and power up the relay...

The dedicated relay is EXACTLY what the OP needs, and his diagram is correct.

We've done this HUNDREDS OF TIMES for people in the shop,
And I don't know how many people on the forums!...
And it's ALWAYS worked just fine for all them.

I don't know why you think it won't work for this guy?

To the OP,

The diode, stripe facing the alternator, will solve your 'Issues' (no longer a problem now!)...

We've done this before, and diodes come in the aftermarket ignition kits for this very issue...

If you get your own from Radio Shack, it will be $1.50,
If you get it from the aftermarket places, it will be around $15 plus shipping.


You are the master! I pulled the wire you said and sure enough the jeep cuts right off with the switch! Thanks for the quick response's been driving me nuts.
No problem man, I've been doing this quite a while, and some 'Issues' keep coming around time and time again, and this is one of them...

I got the relay at Advanced Auto parts.
It's good for what you are doing, since the HEI will draw about 5 amps, and those cheap relays are rated at 30 amps, but are only good for 15 or 20 amps.
This application is about tailor made for the relay you are running.

How do you guys know this stuff?
40+ years of experience.
Lots of breaking parts I couldn't afford to replace, so I leaned how things worked so I could fix them at home...
Then it turned into a full time job and fairly lucrative business for many years.

One more question.
I went to radio shack and got a diode.
They didn't have the 276-1443 or -1444 but the did have 276-1143 and -1144 so I got a pack of the -1144's. 3 amps- 400PIV ? sound right?
Yup, I screwed up the numbers, and either of the ones you listed will work with MUCH room to spare.
You are looking at about 1 amp maximum, and about 14 volts max.
PIV means PEAK INVERSE VOLTAGE, and at 400 you are NEVER going to burn or overheat that diode.

Rectifier Diodes are MUCH TOUGHER than the little bridging diodes or other type of diodes, so I use them.
They just last even when I abuse them! (good thing in a Jeep!)

Maybe the numbers were off a little....just sound too close to be wrong.
Yup, I screwed the pooch... Something that happens daily! I get used to it, but other people still make a big deal about it when it happens...

I always challenge them to keep this many part numbers from 11 dozen suppliers right in their heads and that usually stops the argument/razzing!

Thanks again!
No problem, glad I could help you get up and running again!

· Premium Member
11,200 Posts
Okay! Pin #87 is ONLY the distributor power. That's the way it should be. However, going back to the origional problem, when you turn off pin #86 the motor HAS to stop. If it doesn't something is wrong and it's NOT a missing diode! In a PROPERLY installed harness there is ABSOLUTEY NO REASON FOR A DIODE (unless you want a "lamp test" capability). Pin #86 should be a keyed 12 volts from the OUTPUT side of the starter relay.
OK, Chet, you are normally very reasonable and respectful...
What's the deal!

#87 is 'OUT' to electrical 'Load' or 'Appliance',
In this case, it's the HEI distributor!

Restricting or Impeding #30 or #87 will simply reduce the amount of current available to the 'Load', 'Device' or 'Appliance' (IE: HEI Distributor!)

You CAN NOT "TURN OFF" Pin #86 (or #85, depending on how the 'Power Up' circuit is wired) once the engine is started.

Back feed from the alternator wiring is going to keep pin #85 or #86 'LIVE' once the engine is running...

With a common ignition, the 10 to 15 Ohm resistor wire at the 'Excite' wire line at the plug,
And the 1.35 Ohm resistor wire would be enough to let the ignition 'Quit' when you turned the key switch 'Off'...

This guy has a relay that activates at a MUCH lower current threshold than the factory ignition did on the same line...

The alternator current back feeding the system keeps the relay CLOSED until you break the connection to the ignition or alternator.

(That was the purpose of unplugging the alternator to test!)

The one simple diode stops the back feed, and since there are at LEAST 9 dedicated diodes in the alternator already (Not counting the semi-conductors in the regulator),
Adding another one isn't an issue...


This would be a better diagram for the wiring,

Since the alternator 'Excite' wire is also powered by the old factory coil wire, the 'Excite' terminal on the alternator will Back Feed the ignition system...

Resistors in place, there isn't enough current to 'RUN' the ignition system on the stock vehicle...

It takes MUCH LESS current to operate/activate a relay...
(That is the ENTIRE purpose of the relay's existence!)

A Simple Diode blocking that back feeding into the relay activation line (#85 or #86) will stop the 'Run On' problme the OP is having.

Or you can add more resistor to the line, but resistance will have to be found that will allow the system to operate with the key 'ON', but allow the relay to OPEN when the key switch is 'OFF',
Which will be a balancing act trying to find the correct resistance...

Diode solves the problem all at once, harms nothing, and will last for many years to come... And it's cheap & easy.
The big 'Plus' is, we done it for years and it's ALWAYS worked!
It's a know 'Fix' to this particular problem
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