Captain Obvious

One other thought... Maybe they're simply tying the positive out right to the positive in on the PCB... It might be a simple PWM to ground through a transistor and the only reason they included a separate terminal for positive out was to simplify the wiring for people who didn't want to put two wires under the same terminal screw? Without having one in hand to do a little reverse engineering I can't tell.

Hmmm... On those pre-canned four wire dimmers, it looks like they're actually DRIVING the output terminals instead of just pulling one of them to ground through a transistor. Two of the connections are easy: Negative in would connect to ground. Easiest place to pick this up would be the black wire at the dimmer connector. Negative out would connect to the low side of all the bulbs. Easiest place to pick this up would be the red/blue wire at the dimmer connector. But the other two connections are a little problematic... You would have to break the original connection between the combo switch and all the dimmable bulbs to insert the module between the two. Hate to suggest that you spend more $$ if you're already in the doghouse, but can't you just pick up a low side switching PWM controller like I used? Something that shares the same low side and just drags the bulbs to ground through a transistor? Would certainly be easier wiring! You'd make up the cost in time spent with your head underneath the dash! You want me to pick one up at the yard and send it to ya? My treat!

Steve, Haha!! Yes, I'll take the blame. I'm glad to shunt the heat since it's harder to feel the impact when I'm so far away. You're one of the people who are partially to blame for this anyway. Showing off your LEDs in Memphis and all. So, about the electronics... The PWM controller is typically a three wire device: First connection gets connected to a source that goes hot when the bulbs are on. Second connection is the interrupted PWM output which gets connected to the low side of all the bulbs you want to light. Third connection gets connected to ground. Problem is that the original pot is a two wire device, so you need to run a new third wire to the PWM controller. Or.... Through a little electronic Tomfoolery I modified the PWM controller circuit inside the box to make it a two wire device instead of a three wire device. I'll get into the details if anyone wants, but I basically traded a small bit of PWM adjustment at the upper end for the ability to eliminate the third rail. So instead of operating from (0% to 100%) mine now operates from (0% to ~98%). I don't miss that upper 2% of "full brightness" duty cycle. And in the unlikely event that you DO miss that upper 2% of brightness, you can switch to brighter bulbs or something. Only other trade off is that I'll need to keep one incandescent bulb somewhere in the system or bury a lowish value resistor in place of a bulb somewhere in the system. So you either need to add the third wire (which is also easy) or you can modify the controller to use two wires instead of three. I decided to modify the controller but either way would work.

SteveJ nailed the "why".... I'm messing around with LED lighting for the dash and the original resistance based pot style dimmer doesn't work properly. The original dimmer pot is 10 Ohms and has to be somewhat "matched" to the impedance of the original incandescent bulbs in order for it to work properly. When you go to LED's, the impedance is so radically different that the dimmer function doesn't work effectively anymore. Besides... It's cool? The PWM controller does contain electronics, but I doubt there's anything programmable in there. It's just a fixed frequency oscillator that they use to drive a variable pulse width output to a power transistor. You turn the knob and it varies the pulse width from 0% ON up to 100% ON. "You seem to be making a lot of brass extendo devices..." Haha! Because I can.

Most vehicles have long since changed away from a potentiometer based instrument dimmer to a Pulse Width Modulated (PWM) based electronic dimmer controller and I've been working on retrofitting one of these newer style electronic dimmer controllers into my 280Z. I poked around the junkyard looking for one that would mechanically fit in the original potentiometer location and settled on one from a late eighties to early nineties Toyota Camry. The main criteria needed are short stubby mounting depth and rotate control instead of a thumbwheel so I could mount it in the original dimmer pot location. This is the dimmer out of a 91 Toyota Camry: The biggest hurdle with this retrofit is that the shaft is too short, and because of that, this became mostly a mechanical project instead of an electrical one. I took the dimmer module apart and took the control potentiometer out: Mounted the pot in a "specially designed fixture" to be able to modify the shaft. I wanted to turn it down a little to fit inside an extendo-shaft. Here's the pot mounted in the fixture and the rough cut brass extendo-shaft at the bottom: I turned the pot nub down a little and bored the end of the extendo to fit onto the pot nub. After the rest of the machining is done I'll epoxy the extendo to the original pot nub: : Then for the other end of the extendo, I machined some splines to fit the original dimmer knob: Here's the completed dimmer next to the original dimmer pot. I glued the shaft together and everything looks great. I didn't mount it in the dash yet, but I did connect it up and it works great. I probably won't mount it in the dash until the off season. I'm going to pull my dash out for some HVAC work and it'll be a lot easier to swap the original pot out with the dash out of the car. Here's the completed dimmer:

I made the extendo contact. It's just a little piece of brass stock that I drilled and tapped for a small screw. Don't remember the size though. About the only dimension that matters is that its not so big that it hits other places you don't want it to hit. Not sure when I'll be in there again, but I'll measure it for you next time if you want. I think I'll have my dash out again this coming off season for some changes and if you haven't fixed yours by then, I'll have my wheel off then and can refresh my memory.

So after I did my steering wheel upgrade, I made sure my horn was working and it worked great. Then one day, I'm out driving around and making a turn and some guy pulls out in front of me. I hit my horn button and nothing. Doesn't work. Get home and test the horn again. Works fine sitting in my driveway... Turns out that my horn worked great AS LONG AS THE STEERING WHEEL WAS POINTED STRAIGHT AHEAD. But if the wheel was turned to one side or another, the slip ring contact lost contact and my horn didn't work. That took me a couple weeks and two near misses on the road to figure out. In the end, I made a little extendo contact and screwed it into place. Works great. Here's my original worn one and my replacement. The new one should last longer than I do.

If you're looking to get rid of the redundancy, you could get the upper warning lamps from a 75. Left side says "CATALYST" and right side says "FLOOR TEMP". That way you could fill all the available locations with unique indicators. I'm an idea guy. Never said they were good ideas though...

That makes sense. The other pics of the car look clean. I was surprised the heater box was that dusty. Good luck with the re-sealing. Hope your toes are toasty and your windshield clear.

Haha! Well as I said. More power to ya! I'm just glad there was a spot for my PO to put my antenna toggle without having to really kludge something together. If it weren't for that unused plate, I'm not sure what he would have done. So you're still running the original radio with the switch in the faceplate?

Glad to help. As dirty as your heater box was though, I can certainly understand why you were thinking a filter was necessary. That thing was a dirty dusty mess! Was the entire car like that when you started?

Agreed!!!

Sounds like a plan. I think there are a couple other threads already about people who have "re-foamed" their heater boxes. Search around a little and I bet you can turn up some ideas.

I assume it was provided in all 75 cars regardless of the destination. OK, so we got the "What" detailed out... Now how about the "Why?" Out of curiosity, why is it you're doing this? I mean, it's obviously a "style" choice kind of change, but it just seems funny to me to replace a perfectly good blank block off plate with a non-working redundant indicator lamp. More power to ya. but just wondering...

Haha! Floppy dirty pieces of foam and vinyl! One of the Z specific stores might sell pre-cut replacements, but I haven't looked. I think most people just use regular hardware store foam and fabricate their own. As for if it's really necessary or not... It's nice for the doors to seal well when you have them in the desired positions., but not a deal breaker if you get a little leakage past them. If you're in that deep, I'd put something in there, but it doesn't have to be perfect?

I think I figured it out... 74 had no fuel warning lamp. 75 had the lamp between the defroster and fasten seat belt lamps. 76 moved the fuel warning lamp up to new position to the right of the map light. So my belief is what you have there is a 1975 fuel warning lamp. In 75 they used both lamps up by the map light for the catalytic convertor warnings Take a look at pages BE-42 and BE-96 of the 75 FSM. Also take a look page 29 of the service bulletin the described the differences between 76 and 75.

And here's a shot of the interior of my old 260. It doesn't have that hole at all. And prior to the 260, the whole dash and console area was completely different. Here's the 260: :

This is from page 16 of the 1977 Owner's Manual. I assume 78 is the same:

George, I don't think there ever were any filters in the heater system, so I'm confused... If you're thinking those floppy dirty pieces of foam and vinyl were filters, then you're incorrect. I think those are just for internal sealing of the duct doors and insulation, not filtering. Is that what you're talking about?

Yes it is my friend... Yes it is.

My car has a toggle switch for the antenna mounted there. I've seen so many cars like that, I've wondered if it was a factory option. I don't know what car that fuel warning lamp came out of. You don't know any of the history? Where did you get the indicator?

Is (or was) the car an automatic? The reason I ask is that the autos had two pickups in the distributor and a different ignition module that accepted signals from both pickups. In the auto cars, it switched from one pickup to the other when the engine warmed up some. Maybe when your engine warms up a little it switches to the other pickup and for some reason you lose spark? If it's a manual car, maybe a PO put in the ignition module from an auto car? Just tossing out ideas that could let the car run OK for a short time and then have it die like you turned the key off. I'm with SteveJ. I would also be surprised if it's a fuel delivery issue. I'm thinking something electrical... If it's fuel, it wouldn't die so abruptly. You'd sputter and cough as your float bowls were sucked dry. And it wouldn't restart smoothly either. You'd have to crank a bunch of times until you had enough fuel back in the bowls to keep it running.

Nice score! Beautiful car, huge building, unlimited refreshments!!

Because of the way the poly bushings work, they make the seals unnecessary. When you install poly bushings, they are designed to be crushed a little when the hardware is tightened and that bushing crush eliminates the gaps that exist with the stock style rubber bushings. You don't want those rubber seals in there getting crushed along with the bushings.

Actually there are seals used with the original bushings. I suspect that many of them have turned to dust or were not reinstalled after some suspension work, but there were seals in there originally. Bunch of discussion in this thread: http://www.classiczcars.com/topic/48661-spindle-pin-rubber-washers/ Here's a couple pics from that thread: