'73 240Z Rear Defroster

[SteveJ]

I was thinking that the fourth wire was the ground. Now I'm going to have to put that on my list of things to do this weekend to examine the accessory relay so I can document it properly.

[geezer]

I understand about the assumption of the fourth wire being a ground Steve. In the case of a standard ISO relay a ground wire or a bus supplied power wire connected to pin 85 or 86 is not always shown in the diagram. If not shown, the origin is usually explained in the accompanying device description as being supplied via a jumper from pin 30, or if a ground, it will state the chassis ground location. These cars were built in an era before the conception of ISO or ground controlled relays and circuits, and although I find the wiring to be relatively simple, it sure is different and leaves a lot to be desired. That's why I am totally redesigning my electrical to eliminate the high resistance/heat. I am a sad sight with my glasses and magnifying glass trying to read these things. I find it frustrating and hard on the eyes nowadays, but it's still interesting. I am thankful we have guys on the board that are finding and making note of these wiring anomalies.

[EScanlon]

While you're at it, please help ascertain for sure where the junction for the Heater Blower branches off from. Does it branch off BEFORE the Fuse Box or AFTER the Acc. Relay? There are numerous "???" items that take careful compilation from several diagrams to try to ascertain what "should" be happening, and it's still sketchy.

Even the wiring diagram I point to shows TWO Heater Blowers. Both yours and Ron's show ONE. However, none show a clear connection for the power going to the Ignition Switch. Track that down just for grins and then try to answer "Where" does the Ignition Switch receive the power it then uses to start and run the car.

Typically a "T" or branch is shown by a round dot over the connection to identify it from a simple cross over of two lines in the schematic. They avoided using the little "jump" marks to avoid really making a mess of things.

Unfortunately after multiple scans, copier copies of originals and copies of copies, the end result is a grainy hard to discern wiring schematic. Then with the advent of computer scanning, those errors are then scanned and someone overwrites a grainy image with new vector line graphics and a mistake is now promulgated as fact. Can you read what the wording on the side of the Ignition, Combination Switch, Turn Signal Switch grid boxes is? How about when the error causes problems as in the case of the two White/Red or White/Black (depending on which schematic and generation copy you see) going to the tail-lights? Which one is which?

The result is that there are many schematics out there, some with tell-tale errors and others with obvious omissions and others with duplicate/contradicting information. This also isn't isolated to the S30, the 311 (Roadster) also has the same problems.

I've been trying to compile and discern as many as I can, but it takes patience to carefully pore over each little line from beginning to end and to do it on a computer rmonitor....and I haven't even begun to look at the 260 or 280 diagrams. Any volunteers?

The final result is that while some assumptions are valid and easily verified, others take several different diagrams and vehicles examined before a guess can be put forth...and sometimes that's what it ends up being...an educated guess.

FWIW

E

[SteveJ]

I'll have to say that if it is an error about the three blue wires going to the accessory relay, Nissan was consistent in it's documentation. It is also marked as being three blue wires in the drawing that shows the different wiring harness sections. This is definitely intriguing.

I'll see what I can track down.

[pak52]

Thanks to all for your help. Now that I have the schem, can anyone tell me where the 20A fuse is located that's shown in line with the rear defroster? Also, just in case, where is the Acc Relay mounted?

fyi-

I bought this '73 240Z new when I was in the service. Had crankshaft problems in '76 - swapped in a chevy 327. Drove it for 4 or 5 more years. Then it sat. I thought I was through fooling with it. Then my son grew up and decided he wanted to rebuild it (with my help), for his car. So... as you know, there is always something going wrong - it's pretty old after all.

[SteveJ]

Thanks to all for your help. Now that I have the schem, can anyone tell me where the 20A fuse is located that's shown in line with the rear defroster? Also, just in case, where is the Acc Relay mounted?

fyi-

I bought this '73 240Z new when I was in the service. Had crankshaft problems in '76 - swapped in a chevy 327. Drove it for 4 or 5 more years. Then it sat. I thought I was through fooling with it. Then my son grew up and decided he wanted to rebuild it (with my help), for his car. So... as you know, there is always something going wrong - it's pretty old after all.

I'll look at my FSM this evening and try to find the location of the fuse.

[EScanlon]

Should be in the fuse box area beneath the warning light panel. It is an in-line fuse holder and not a part of the fuse box. It may be mounted to the side of the fuse box, but that's unusual.

The Accessory Relay, in your year should be on the upper part of the Passenger Kick Panel. I believe the Heated Window Relay is also mounted there, but I'm not 100% sure.

There were some crazy changes in 72/73 that make it difficult to ascertain exactly what and where. In that time frame, the connectors for the harnesses went from being loose and then just held to the body by the rubber clamp "fingers" to being incorporated to a "Buss" box on the Passenger Kick Panel.

FWIW

E

[geezer]

It's not portrayed very clearly, but in the microfiche the Accessory relay for '73 is shown on the Rt/Passenger kick panel. They don't depict the inline fuse but it is likely in the same location as mine, which is just below the harness clip on the Instrument Panel, just to the right of and behind the Heater Control Panel. And guess what, mine is a blue wire even though it is shown in the diagram as a R/L.

[EScanlon]

Ron;

Actually, it IS supposed to be a Blue wire. This is one of those anomalies I was referring to. Follow the R/L wire coming from the Acc Relay and note where it connects to the Blue wire going to both the Blower and the Defrost circuit....THAT is where it changes color. Nice huh?

There are numerous instances of this.

But nobody has pinned down where the Ignition Switch gets it's power from. This is one of those...."Can you find the Spot?" games. I'm asking it this way to confirm one of my "deductions" based on about 6 different diagrams.

E

[geezer]

Yes, I noticed that just after my last post while comparing some of the diagrams I have. One other thing I was puzzled over was the device labeled "COOLER" on a supposed Early Z diagram. It is shown spliced into this same blue wire and also has an inline 20A fuse. I was wondering, what the heck is a "COOLER"? Is this what they are referring to instead of the Blower Motor? I guess so. Sorry for the deviation but it does tie into the same circuit.

[pak52]

I found the fuse. It's ok. It looks like the switch is bad. I noticed that when I jumper around it, a relay clicks on. Funny - the schematic doesn't show a relay in line. Another one of those oddities.

[SteveJ]

Did you test the switch for continuity?