Captain Obvious

Well that's sorta too bad that it passed. Makes it harder to find the problem. Next thought is that the alternator is doing what is expected of it, but the fusible link connection between the alternator and the battery is shaky. I haven't studied it that closely, but it appears that the alternator will still run certain parts of the car even if that link is gone, but things like the headlights and the FI will run off the battery and not off the alternator. And if that connection is intermittent, you'll get swings on the voltmeter on the dash as the alternator is intermittently presented with the heavy load of the battery. And if that link is making connection, but not a good one, it's likely to heat up right at the connection ends. So... You've got four fusible links in the engine compartment on the passenger front wheel well. Three of them are one color and are smaller than the fourth. My 78 FSM is blurry and it's hard to read the wire colors, but I believe the three smaller ones are brown and the fourth larger one I black? The one I'm concerned with is the black one. With the engine running and a meter on the alternator output, wiggle that black link around a little and see what the meter does? If that fusible link doesn't make good connection the alternator won't charge the battery correctly. If you see anything funky on the meter (heck, even if you don't), pull the link off and make sure everything looks clean and shiny? Not green and crusty. While you're in there pull all the links and make sure they're all nice and clean. Just make sure you don't mix up the colors.

TomoHawk, The original festoon bulb is what they considered a 31 mm festoon, but that's measured tip to tip, so it's hard to draw any correlations without actual drawings of LED replacements. I measured the two lamp housings I have here and came up with the following: Distance between the inside edges of the brass contact clips = 0.67 inches. Distance between the plastic inside walls of the whole housing = 1.47 inches. That means in order to fit comfortably into an unmodified location, the wide PCB portion of the bulb must be less than 0.67 inches wide, and the overall length of the whole bulb (tip to tip) must be less than 1.47 inches. That bulb you linked to on Amazon looks very promising mechanically. It looks like it would fit better than what I used and I don't think you'd need to modify the contacts. If you could get that in warm white, it looks like a winner. I bet the ones on Amazon are cool white though (what you're calling hyper). The bulbs I used with the PCB turned the other way. You can see from the dwg why I had to remove some material from the clips to get the PCB to fit. I also had to file a tiny bit off the tips of the cones to get it to fit inside the plastic housing, but it was a small amount and very easy to do: Maybe you could dig up a mechanical drawing for the bulb you found?

Wait a minute. I want to make sure I'm doing the math right... I can give up the wife for a car like that?

I can't see the control signal tubing at all. I suspect it's been removed and disabled ever since he swapped in the older SU's. There is a vacuum port on the original rear flat top carb that is a ported signal. "Ported" such that there is no vacuum at idle or at WOT but only at a point between the two at "light cruise". That signal is what was originally used to control the amount of EGR. The round top SU's have no such vacuum connection on them at all, so I assume that control line is simply capped off rendering the whole EGR system inert. There's a small electric solenoid valve between the EGR control valve and the valve cover. Can't see it in your pic because it's tucked behind the device you were curious about. That's also part of the system.

Yeah, those will work fine but aren't stainless. No biggie, but I just prefer the OEM style.

I was originally going to suggest that it's easier to pull the whole dash first. If you've got small hands and are part contortionist it's not "really" necessary, but I've found the extra time I spent pulling the dash was more than made up for by the ease of working on the heater system after I had done so. No matter how you look at it, pulling the heater core out is a PITA. I feel for ya Charlie. Be careful of your back.

That's the EGR control valve. (EGR started in 73 which is why your 72 didn't have this device.) The purpose of the EGR system is to reduce oxides of nitrogen (NOx) from being released into the atmosphere which is a good think for the next generation. There isn't really any performance reason to remove it. It's only active at light cruise and is disabled at higher throttle positions. Looks better without it, but no reason to do so for performance. I'm assuming he's still running the original carbs? Because if not, I'm not sure where he's going to hook up the ported control vacuum signal...

I couldn't get the ebay link to open, so I can't tell for sure, but I've never seen small hose clamps that were as good as Nissan OEM. The OEM ones are full stainless and everything I've ever run into aftermarket was at least partially plain steel. If the ones on ebay aren't 100% stainless then just go to a junkyard and grab a handful off Sentras and Maximas.

Glad to (try to) help. My additional advice would be to take it to SteveJ's place and distract him with a Digi-Key catalog. Tell him the centerfold this month is excellent or something. Then when he isn't looking, swap your alternator with his.

Howdy Neighbor! I'm in the burbs north of the city. Car looks great! Congrats! I'm no expert, but if you need help, give me a shout. I know some stuff.

Recent discussion on the same issue. Maybe some help in here? http://www.classiczcars.com/forums/electrical-s30/53259-parking-interior-light-fuse-melting.html

Wait a minute... Last I heard, you were driving around with your headlights on and your alternator had failed. Your battery voltage was dropping? "A minute or two later, I was getting 12.8 and slowly dropping. By this time the battery was reading 12.5." When I said that it either works or it doesn't, I meant that there really isn't much else in the whole design that could be an issue with the internally regulated system. Other than a loose drive belt or a bad connection, about the only thing that can go wrong is inside the alternator itself. The only other thing I could come up with is if your CHG lamp is burned out, there's a chance that your alternator won't get itself up over the hump of producing current. But if your CHG lamp works normal, then that shouldn't be the issue. Take it out and have it tested or borrow a known good one if you can and throw it in and see what happens?

Yeah, that sure starts to sound like marketing propaganda aimed at increasing your own sales by torpedoing someone else's product. I used to take my GM to 6000 RPM every once in a while and it never gave me any trouble doing that.

I'll put in a third vote for this. The internally regulated system either works, or it doesn't. You mentioned your charge lamp flashing yesterday... Does it still work today? The CHG lamp should light up when you turn the key to "ON" before you crank the engine. Does it?

Yeah, I grew up on the incandescent as well and completely understand. That whiter than white LED thing just doesn't work for me either. I don't know if it's all mental, or age... But I just don't feel that I can see as well with the cool white shade. The LED bulb I installed is a little whiter than the stock incandescent, but I find the whiter bulb offsets the yellowing old plastic lens of the dome light. End result is that I think it looks like it's "supposed" to look. Original shade, only brighter. Haha! I don't think my hair brained weird stuff I spend my time on is going to scare MSA or any of the other suppliers.

I settled on Part Number: 3710-WWHP6. It's a 37 mm long festoon with 6 LEDs in warm white. https://www.superbrightleds.com/moreinfo/festoon/3710-led-bulb-6-smd-led-festoon/661/. It was a little longer than what fit comfortably between the mounting clips and I had to grind a little off the connector clip fingers in the lamp housing to get it to fit between the fingers, but it's a once and done job, I've very happy with the outcome. Brighter and not harsh. Hot the "specifications" tab and you can choose what color you want. Lots of people like the "cool white" color, but I'm not one of them. I find the bluish "cool white" light harsh. I bought "warm white" and I love it. Here's some pics showing what I had to do to the mounting clips to get the bulb to fit. I used a carbide burr on a dremel. Don't get tiny brass slivers stuck in your fingers (or eyes): And even though you can't tell much because there's nothing else to compare it to, here's the obligatory "ON" pic: If you don't want to deal with modifying the clips to get the wider festoon to fit, you can sacrifice some brightness for ease of installation and get a 4 LED shorter version instead: https://www.superbrightleds.com/moreinfo/festoon/de3175-led-bulb-4-smd-led-festoon/238/1129/ Part number 3022-WWHP4 is the shorter 4 LED version in warm white. Lastly, I don't think you're going to find a "warm white" shade at a generic AP store. Seems most people like the bluish LED color of the "cool white" bulbs and that's all I've ever seen on the shelf. So if you want cool white, you might be able to find it local, but if you want to control the shade, you'll probably have to mail order it.

Gotcha. Step 0 - Buy or borrow a meter. :paranoid:

Well I sure hope that's truly the issue and don't want to rain on any pre-parade celebration, But... Your fuel filler cap is supposed to prevent vaccum buildup in the fuel tank. Shouldn't really matter if those lines were blocked off or not (unless you've got a non-venting fuel cap). I mean, I wish you the best here, but don't want you thinking you've found the smoking gun. Yet. Don't shoot the messenger?

And the problem BETTER go away once the speedo is disconnected! The dimmer control gets it's wires from the speedo, right? If the speedo is disconnected, so is the entire illumination control circuit? So what are you gonna do once everything (except the speedo) is disconnected and the problem still occurs? :ogre:

I know the 74 was transitional in spots, but according to the wiring diagram, your hazard switch DOES have a light on it. Either your bulb is burned out, your connectors are corroded, or maybe that's where your problem is originating. And about the other three... Defogger, Choke, and Seat Belts? None of them are controlled by either the dimmer or the combo switch. All three of those will always be full bright when their respective switch is turned on regardless of the position of the dimmer or combo switch. For example, the CHOKE indicator will come on full bright anytime the choke lever is pulled regardless of the combo switch or dimmer positions. Nothing is impossible, but it's unlikely that any of those have anything to do with the problem you are having. If I were you, next thing I would do would be to disconnect the hazard switch and see what happens. And you've been disconnecting things one at a time and then what? Reconnecting them or leaving them disconnected? If you've been reconnecting them, I wouldn't do it that way. I would disconnect something and leave it disconnected until you get to the bottom of the problem.

And I'm not sure if this is the most appropriate place for this, but since it's related... While reviewing the wiring diagrams for the 260, I turned up a couple mistakes. I don't know if these are old hat already known issues, but since I'm not the keeper of 260's electricals (Steve?) I thought I would hand off to the experts. Here's a portion of the 260 (manual trans) diagram: Here's what it should look like: If there is a collective "Problems Found on the 260 Wiring Diagram" thread, this could go there. If there isn't a thread like that already, maybe one should be started? I know I've got at least one other 260 problem that I've discovered.

boosd, SteveJ summed up the problem when he said that the Green/White wire is somewhere shorted to the Red/Blue wire. Problem is figuring out where that short is. Here's one idea that might help track it down: Park the car in a dark spot (dark garage or just wait until it's dark out). Turn the dimmer control to full dim. Turn the combo switch to the first position (turn on the parking lights). The parking lights should all be lit and the fuse should not be glowing. Then quickly turn the dimmer to full bright and look at your interior illumination lamps. Don't keep the dimmer full bright for long because you're going to pop the fuse or burn something up again. But quickly look at the following: speedo tach water/oil amp/fuel clock lighter heater control panel radio hazard sw If you can't look check all of them in a second or two, just turn the dimmer back to full dim and give it a minute or two for everything to cool off. After a cool off period, do it again to check the stuff you didn't check the first time. If any of those devices are NOT lit, I'd start there.

Steve, Haha. Yeah, that's one of the things that gives me trouble with distance diagnosis. That and the ability to explain things in a way that others understand. It might make sense in my head, but being able to convey that info without writing a novel is a different story! I found the same thing as you did with the buried splices. I'm planning some electrical upgrades (like headlight and starter relays) and have dissected a cadaver engine compartment harness for investigation. They did the same thing there. Splices crimped and taped and then buried in the outer layer of tape. Just hoping the fault isn't buried...

Yup. That's what I'm thinking. The thing that worries me the most though is that all of this started after some melties happening. I just hope it isn't melted insulation buried down in the harness somewhere. If it's a bulb, even I could probably find it. However, if it's melted and shorted insulation somewhere in the harness, I'd need one of those RF signal sniffers.

Maybe it's just me, but I'd much rather have that 280 than that series 1 barn find (maybe hit in front maybe not?) that's on ebay for stupid money. That 280 is fantastic. I still don't think I'd pay 25K for it, but it sure is beautiful.