240Z gauge electrical problem AGAIN!

[RS02]

Hi. Lance here. I finally got around to rewire my 1971 240z. It had a L28 and a faulty wiring and I'm very confused. So, I found a small metal box on the back of my speedo. It have a Yellow and a Yellow/black wire coming out and a red wire that hooks up with the speedo. I teared apart the old wiring and found the yellow one is connected to the IGN Black/White wire using some sketchy electrical tape, and the Y/B one is routed all the way to 4 big 2x5 connector that connects to the engine bay harness. I'm guessing this is a mix matched setup? Voltage regulator is not wired either. Since I'm rewiring the whole thing I just need to know what the heck is this small box. It outputs red about 11.6 volt when battery is connected via Y, and nothing at Y/B. I searched online and found this image of a 260z gauge that appears to have the identical box. It seems those green wires are the Y and Y/B on mine. I did some research online and found out nothing. Have anyone got a idea of what it does? I'm testing the gauges and the speedo and fuel gauge is not working.

[Zed Head]

Do the number font styles match the other gauges?  That might tell you if it's a 1971 gauge.  Many emissions devices have a speed detector attached to the speedometer.  You might read the various Emission Control chapters to see, or look at wiring diagrams.

[Chickenman]

I believe that unit is the Voltage Limiter for the gauges. Water and Fuel gauges work on 9 volts. The rest of the car works on Battery voltage which is higher. This instrument Voltage limiter knocks the alternator regulated output down to a staedy 9 volts. This produces more accuracy in the guages and also reduces heat buildup in the operating coils in the gauges. We used to replace them quite often in the dealerships.  Some models ( not all ) had a separate part number for the instrumentation Voltage Limiter. Some you had to buy a complete Speedo or Tach to get the unit. I can't remember if 240Z had a separate one available or not.

RatsunNet has an article on how to replace a defective Instrument Voltage Limiter with a generic part:

http://community.ratsun.net/topic/54598-bad-gauge-cluster-voltage-regulator-easy-2-fix/

 

Edited November 25, 2016 by Chickenman
Corrected link

[Chickenman]

Original 1970's Instrument Voltage limiters are next to impossible to find. A Voltage limiter from the 1980's and 1990's can be retrofitted. 24866-54A00 is a popular model. You can still buy them from dealerships or find them in Bone Yards. Pathfinders and Trucks use the 24866-54A00.

You may find the newer V/Reg has three wires. Extra black wire is for a dedicated ground. Old 1970's style grounded through case.

 

 

Edit: 24866-07G05 may be a better choice. Cheaper and only two wire

Edited November 25, 2016 by Chickenman
Added pictures and link to 24866-07G05

[sweatybetty]

i dont see anything on the electrical schematic showing a voltage regulator for a 72. did they have one in the early 70's?

[Chickenman]

Yes they did. On all models of Datsuns . ( Edit: Correction... Apparently not on all models according to references below ) If you read the complete article from Ratsun.net you will see a full color diagram for a 1969 Datsun 510. The Instrument VR is shown in that. Datsun 510's 240's 620's 520's and 1600/2000 sports cars all had Instrument voltage regulators. They were used from the 1960's right through the 1990's. If you had a magnetic coil operated temperature gauge or fuel gauge they all had them. Ford's, Chevy's, Toyota's etc, etc. The magnetic coils were designed to work with with 6 to 9 volts maximum.

Not all the wiring diagrams show the Instrument VR because it usually came as part of the Speedo gauge. Same with the Parts manuals. I'll have to have a look at my 1976 280Z Factory SM to see if it's shown.  Some guys retrofit a Ford Mustang VR because they are dirt cheap. But you can easily find wrecked Nissan Pathfinders and Pickups on the Boneyards. Sentra's had them available separate as well, but the part number is NLA.

Both the 24866-54A  and 24866-07G05 are solid state, where as the early 70's models were a vibrating coil type very much like the alternator V/Reg.

 

Here's a partial listing of some available and discontinued Instrument VR's. Not the ones that say Knob-Meter as a description  is likely a misprint.

http://www.courtesyparts.com/?p=catalog&mode=search&search_in=all&search_str=24866

 

 

Edited November 27, 2016 by Chickenman
Edited for accuracy

[Chickenman]

Here is a copy of the RatsuNet wiring diagram that shows the Instrument VR. ( Lower right hand corner with Temp and Fuel gauge ) Not usually shown in wiring diagrams because the part was not always available separately as I mentioned.

 

 

[Captain Obvious]

Datsun referred to that device as an "amplifier", and as Zed Head mentioned above, it controlled the actuation of some of the emissions controls starting in 74 (maybe 73?). There is a very small mechanical switch built against the speedo needle and that switch opens (or closes?) when the speedo needle reaches a certain speed (10 mph). The switch is very small and they use that amplifier box to control more current than the switch could handle directly. 

As for a regulator for the gauges, the Z dash gauges do not utilize an external regulator like some other cars. Instead, each gauge has it's own internally built in regulator. There was some discussion of that function in these threads:
http://www.classiczcars.com/topic/44557-has-anyone-successfully-repaired-bimetal-contacts-in-a-dash-gauge/
http://www.classiczcars.com/topic/49186-curious-problem-with-my-gauges-question-about-wiring/

As well as this source that is Jeep related, but the theory is the same:
http://civilianjeep.info/Strenk/Gauge%20web%20page/WebPageGauges1.htm

[Chickenman]

Yes, that could very well be an " Amplifier " for the speed switch as you mentioned. That would have to presume that the Speedo shown in firts post is a later model than a 71,

As for the Z cars using separate VR's in each gauge, I have to wonder why they would have done that? Seems a more troublesome and expensive solution than using a single Instrument VR as they did on all most other models. A single Instrument VR were used all the way back on 16600/2000 Sports cars, 510' 520 PU's and on some model right through the 80's and 90's. It doesn't make sense why they would change the setup on the Z cars. Edit: But obviously they did... as the 620"s had the VR in the gauges ( Bimetallic vibrating points ) , maybe 720's as well. But then they went back to a single solid state single VR with the Pathfinder and D21 trucks and a lot of the sedans. 

Another question. Nissan parts catalog lists a " Shunt " in the " Meters " Parts page.  Part #24845-N3401. Illustration #18. What does this do? Is it some sort of resistor that drops the voltage? Only from 73/08 to 75/07 ???

http://www.carpartsmanual.com/datsun/Z-1969-1978/electrical/meters

Edit: I've edited my Post #6 above to correct inaccurate and irrelevant info.

 

Edited November 27, 2016 by Chickenman

[Zed Head]

Found the earliest reference in the Z manuals from 1973.  Looks like the very early version of the BCDD maybe, with a speed-activated throttle opener.  Can't find it described in the chapters, though it might be there.  Images from Body Electrical.  1972 compared to 1973.  The GB wire at the speedo is the actuator for the relay.  And people think that carbs are simpler than EFI....

To the OP - that doesn't seem to be a 1971 speedo.  And with no throttle opener solenoid you don't need to worry about the "box" on it.

[RS02]

First of all thanks for all your replies. I think the "emission theory" is probably right. The unit is connected to 12v ign and speedo. the other wire does not output anything when 12v is applied to ign. So I stripped the wiring and found the mystery wire goes into engine bay. I'm not sure about this car's history. But is seems like someone had put a 280z short block and a 260z top and carb into this car. He probably put the emission in it too. Otherwise it might be a throttle opener... who knows. But since I don't care about the old wiring I might just leave that alone and see how it goes.

[jonbill]

Hi, apologies for the thread resurrection.

My 72 California 240z has one of these relay thingies attached too.

Do you think it likely a 72 car could have this originally, or do you think it has been retrofitted?

Just curious. It's not staying, same for the EGR and other emissions stuff 😀.