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Choke season is here I'm afraid.


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Yesterday I had my first successful short test run in my '72 510 with the L20b transplant (after last week's clutch problems and both clutch cylinders now replaced). So on to a few dozen details to be somewhat roadworthy. I woke up to 3 or 4 inches of snow this morning (my shop is the great outdoors), so getting the electric choke hooked up seems somewhat important. I've read several back posts on choke hookup, but for some reason I can't find a stray wire that is hot with the engine running. I have an idea my alternator isn't working. If that is true, would that kill the 12V to the choke wire? Anyone know the wire color for the stock choke wire and location where it comes out of the harness? Is the choke wire fused? Location of the choke relay on a '72? Finally, for temporary running, what happens if I run a wire from the coil to the choke? I've got a matchbox dizzy and the ballast resistor is bypassed if that makes any difference. I know this isn't the proper place to pick up the 12V, but I'd like to get in a few test runs around town before I head out the 12 miles through the country to where Reg will fix my crashed door and fender.



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Thanks all for the quick replies. I should be able to figure it out after I sweep off and get to the car. Pics of a not-hooked-up-choke would be boring so these instead?




Unhappy flamingo!




Unhappy 510 cause of the snow, but reeeal happy to be running after 5 years or so.


Len (and I'm reeeal happy too)

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The relay needs alternator output to give choke heater. This is so that if the car is warming up in the driveway and you go in for another coffee and it stalls (no alt. output) the choke won't continue to warm up while the motor remains cold. The car would be very difficult to restart without the choke and even harder to drive.

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Update from today - Plugged the choke wire into the Blue wire coming from the harness at the firewall. Before I posted my question I thought this looked to be the most likely wire, but as I said, I couldn't get voltage there with engine running. Today I cleaned the 2 prong plug on the back of the alternator and a couple of other minor details. Started the engine and watched the choke plate gradually come open as it idled. So that seems to be fixed.


I made sure the Alt light comes on when the switch is in the On position and engine off. When the engine runs, the light stays off. But when I test at the battery with a voltmeter, I'm only getting about 12V, rather than the 14V or so my 200SX puts out at high idle. I seem to recall there is more than one diode in an alternator and having one go bad can reduce the voltage without the alt being completely dead. Maybe that is what is going on. I need to retest tomorrow. I was getting tired late afternoon when I was doing this, so I may have missed something obvious. And this is still an external regulated alternator, so if it is bad I suppose it is time to convert to internally regulated.



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Rev it to 1200 RPM and check the volts (factory procedure). If 12V, you might have more corroded connections.


One diode won't drop it all the way to 12V, but usually causes a tell-tale whine.


Voltage should be 14 or more with headlights OFF and fully charged battery. In very hot weather 13.5 or better is expected.

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Another update: I swapped in another alternator, one I think I got as a spare for my 200SX, lots bigger anyway and I'm assuming is internally regulated. I unplugged the regulator and made a couple of short jumper wires to make the connections across the regulator harness plug . I want to be sure everything is working okay before cutting the plug off the regulator and hooking those wires together. Oddly, when I jumped the white to yellow wires, a nearby relay (I'm thinking the choke relay) kicked in with a bang, so I unplugged it. I'm getting 14V or better at the battery on fast idle now.


I'll run a wire from the choke to the + post on the coil for now. I've used a test lead with alligator clips hooked that way and choke opens up fairly quickly after starting. So I think I have my wiring problems somewhat solved. Thanks again to everyone for the help. Amazingly, after sitting for 5 years, the tail lights and turn signals still work just fine. Headlights on one side are really dim, so I need to clean some connections.


But my weird clutch problem is back, so on to solving that tomorrow if it isn't raining. I have a premonition I may be pulling the tranny again to see what is happening in there. But it is all fun and entertaining.



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Yeah, I did a temp fix to test my clutch problem and drove around town some. Much farther than the previous down the highway a block and back. It really feels good to be driving the 510 again even with all the bugs yet to fix. Maybe the clutch problem is in the length of the master cylinder rod and I can fix that with out pulling the tranny. Of course I've thought before several times I had the clutch figured out, so I'll just have to work on the rod and see if that theory pans out. No clouds of smoke from my IR alternator conversion either. No horrid sounds from the Pull n Save dogleg, although I haven't tried it in 5th yet. The exhaust is a blown out glasspack with a foot of pipe behind and so loud there could be a lot of engine/tranny I'm missing. If the rain holds off tomorrow I'll adjust the valves and fiddle with the clutch master rod. I don't know if I'm going to be able to turn it over to Reg to have him do body work. I just want to keep driving it!



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Might be better to disconnect the choke heater relay. Your 510 should be ok but on my later 710 converting to an IR alternator will cause the relay to stay on even with the ignition OFF. It's a small drain but over several days will kill the battery.

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That is exactly what my stock choke relay seemed to be doing. It was kicking on as soon as I did the wire hookup to bypass the regulator. It was getting dark enough yesterday I unhooked a battery cable and could see slight sparks to the post, if the choke relay was connected. I knew that would equal a dead battery so I unplugged it. I've read several threads on IR conversion and never saw any mention of unplugging the relay. Although several mentioned replacing the stock relay with a new12V one. I guess that implies unhooking the old one.


I feel a little more confident I have my clutch problem fixed. But I want to be really sure it is fixed before I post a rant about a Made in China master cylinder. I thought I had the clutch working several times before and was wrong. I plan to do a new post on my clutch mishaps when I'm sure it is really fixed.



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Some of the early alts used a 6 volt supply to the relay or ???? there was some reason why it works on them by using the two jumpers BUT on later IR alternators it won't. I had to disconnect the yellow wire on the relay and tape it up. I ran a wire from the idle cut solenoid to the relay. Now it is on only and always, when the ignition is on.



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Len, which wires did you jump after unplugging the regulator?


6V or 12V doesn't matter. The N connector would still output 12V. Some Datsun choke relays are wired differently and that maybe why changing the relay "fixes" it. But wiring -- depending on how it's done -- doesn't mean you have to replace the relay.

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I followed the IR alt swap article in DQ Vol.0!. Issue 2. https://docs.google....WEwNDk3Y2E2M2Q5 It says to "Splice the white wire to the yellow one. Splice the white/red wire to the white with a black stripe." This is what I did, using the color code on wires from the harness to the V. regulator plug (not the wires on the regulator itself. I didn't look at those, so I don't know if they are the same color code as the harness wires). Again, this is a '72 if the wire colors have changed over the years of 510s. I'll double-check my hookup when it stops raining. When I plugged in the jumper wire to connect white wire to yellow wire and the choke relay kicked in, I did check to see I had the correct wires, but light was getting dim, so it is worth checking again. I know it is charging at the battery 14V or better.


datzenmike - to be sure I understand before I start whacking wires, you are saying I cut the yellow wire going into the choke relay. Tape off the stub to the harness. Run a wire from the idle cut solenoid wire to the yellow wire going into the choke relay? Then the choke relay can be plugged back in and work normally?


I've never understood the recommendation to replace the original choke relay with a 12V one. There is kinda vague reference to the original relay being 6V, but I've never understood why. I don't know where the 6V is coming from. I can understand the original choke relay not being really heavy duty and maybe failing from old age, but the 6V/12V thing escapes me. Maybe it is all a Datsun online urban legend which keeps getting repeated over and over. Needing to rewire the feed to the relay makes sense to me.


Thanks again guys for all the answers. I seem to have a working system now, but it is great to learn the "why" on some of this.



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Yes, the relay 6V/12V thing I'm sure is a legend. Why would the 240Z use a 6V relay for the fuel pump?


4-SPADE RELAY 25235-P0101

* 710 1974 auto choke

* 510, 521, B110 auto choke

* 240Z fuel pump relay


Instead of "splicing" you can use a jumper wire in the regulator connector. I use female spade connectors crimped to a piece of wire, like the original wiring loom did. I think some guys want to remove the connectors to hide/clean up the wiring, but that could make troubleshooting difficult.



Run a wire from the idle cut solenoid wire to the yellow wire going into the choke relay?
That will work, but is easier to run the wire straight to the choke and works the same with one less component to fail. Just unplug choke relay and run IGN feed directly to choke (IGN feed such as the one to the idle cut solenoid).



Splice the white wire to the yellow one
That is how Datun wired IR alternator in the newer harnesses. White is 12V unswitched (always on) and yellow goes to the stem of the alternator T-connector. It connects the Sense terminal to the battery (always on).


The problem with this wiring is in older cars, the Y wire also goes to Choke Relay and causes it to energize the relay -- always on. In newer cars the Relay is 6-pin, wired oppositely, so no problem.



Dime Quarterly, page 9

choke relay ... Use the WL wire (switched on with the ignition) to power the relay coil.
Which effectively means to actually re-wire the relay. Normally the relay coil is powered by Y wire.


Dime Quarterly, page 9

Run a power source—with an inline fuse—from the battery through the relay to power the electric choke/idle solenoid (if fitted). This lessons the current flowing through the ignition switch, and powers up the choke heating coil when the ignition is on.
All right, two important things here:

* Choke will be heating any time IGN is on (just like wiring the choke direct)

* There is an assumption that choke heater uses high power, hence needs a relay. But that is not true, as the factory wiring used the IGN switch to feed the choke heater. The relay only switched it off/on.



Choke Heater powered by IGN switch


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Here's what you can do on a late 710 when swapping in IR alternator -- no new wires needed, but only three short jumpers.


Blue "b" jumper connects Sense to Bat (as in factory IR wiring)

Red jumper connects Lamp to CHG lamp

Green jumper connects Choke Relay to IGN




The only problem is the dashboard Brake warning lamp. The choke relay switched the Brake lamp on when Key ON, Engine OFF so you could tell if the warning lamp was burned out or not. That will no longer work.

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Reading all this info, it sure seems the choke relay can be eliminated without any problems, unless the engine dies while warming up and the key is left on. That must be the reason Nissan included the relay controlled by the alternator. But it is an important feature for the normal motoring public.


Looking in the FSM for my '79 200SX with IR alternator trying to figure out the wiring for that electric choke (still haven't quite figure it either), I noticed there is a bi-metal switch in the choke housing. It looks like about the time the coil spring heats up enough to let the choke open, this switch also opens so there is no more power supplied to the coil spring. Does that sound correct? Probably one of those things everybody but me already knows.



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Possibly. I always assumed it's powered all the time engine is running. The current is highest at first but within seconds drops. I measured my choke at 10 ohms cold at 46F degrees (so it should draw max of 1.2 amps @ 15 volts). My Holley 5200 choke read 50 ohms (theoretically drawing 0.28 amps). Reportedly, some american car chokes can draw 5A or more.


The bimetallic element is the spring. Because each side of the coil is a different alloy, that's why it gets looser/tigher as the temperature changes. The small choke heater element under the spring is what draws the current.


Choke only needs a 20 gauge wire, so feeding off the existing 16 gauge Datsun wires mean there is not a significant voltage drop. That's one reason why feeding it off the ballast resistor is OK (Datsun uses heavy gauge wires compared to american cars of the same vintage).


Or better yet, use the Datsun factory choke wiring -- which is at the choke relay connector. Unplug the relay and put a short jumper there and it's all factory.

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Need to correct my previous post. Reading the FSM more tonight and it seems there are two heater elements in the auto choke housing to heat the bi-metal spring (remember this is a 1979 model year manual. May not apply to earlier years). The switch I saw in the wiring diagram allows the second heater to kick in when the first heater has raised the temp enough (I think it said 50F). The idea is with the second heater on too, the choke plate will open faster. I'm going to try tomorrow to post the section from the FSM on this so anyone following this thread can read for themselves, rather than trying to understand my explanation.


So I think you are right, the heater(s) draw current as long as the engine is running, or as long as the key is On if the auto choke relay has been eliminated.



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