Captain Obvious

Yes, evap, vapor, CARB... All the same thing. I wasn't correcting you at all. "Evaporative emissions control system" is the official name in the FSM. You were closer to that than I was. It's all good! The evap system uses that goofy check valve-ish device between the tank and the carbon can. You can see that device hanging out in this pic, near the bottom: On the tank side of that check valve, there could be some pressure buildup (due to a purposely high "cracking pressure"). But on the carbon canister side, there should never be any measurable pressure in that line. Point is... If it passes air, you should be OK. Smoosh it a little, or just let it be. The LAST thing I would do is cut it and introduce more leak points in the system.

Gotcha. So when you go back, pull off the brake master cylinder first. Easy-peasy and no flight suit required. Easy job up in the engine compartment. Once the M/C is off, take a look at the area where the master bolts to the booster... If it's clean and dry inside and not wet with brake fluid, then we're a GO. If it's all rusty and paint a-peelin from brake fluid, then just leave it. But if it is clean and dry, then the rest of the work is done down by the pedals. One pin with retaining clip, and four nuts. I've been able to reach all that stuff kneeling outside the car. I haven't had to resort to laying down face-up on the car floor. Not that bad. A bad day at the junkyard beats a good day at work. And much thanks if you grab one for me!!

That is the vapor vent line. If it passes air, it's probably fine the way it is. But if you get energetic, you might just smoosh the outward bump back in a little. That might help open up the ID a tiny bit more. If it bugs you.

Bummer. I didn't know about the glass specifically, but I'm not surprised. Just about everything else is different with the 77-78 doors. So, you mentioned the brake booster... Did you grab one? Sure I'd pay $25 for one that is dry and not rusty inside.

Thanks. Me too. I'm headed to the first doctor tomorrow. I suspect this is a season-ending injury...

Gotcha. Working back through PO's work is always tough. Hope the rest of it goes smooth!

Chuck, I normally make it to this show, but I don't think I'm going to make it this year. I'm nursing a recently attained sports injury and am putting most of life on hold for a little while. Else, I would take you up on your offer.

It's clear from the scratch marks on the little metal tabs of that switch that someone has opened that thing up in the past. I'm sure it's all related. Maybe the wire's solder joint was weakened by that process, Maybe they took it off completely during that process and didn't do a good job of putting it back on. Maybe the headlight side rocker inside the switch was burned beyond recognition so they swapped the one from the running lights over. There might not even be a rocker on the running light side if that's the case. Maybe they took that wire off intentionally to use a separate mounted switch somewhere else. Just thinking out loud as to why that switch and wiring is the way it is now. I think you have identified the "what". I'm just musing about the "why".

Glad to help. All that research done, however, I have little confidence of exactly what style (year) will arrive when you order from rockauto. The most important takeaway is that it probably doesn't matter. So, about the gas tank... Didn't you already have the tank done? Why is it costing you more money?

My pleasure. Glad to help. Steve and Dave know the system inside and out, but at least I can do that much.

Haha! Actually, I stand by my answer. The OP was asking about the brake light switch, not the T/S switch. I was responding to the question about the brake light switch when the OP raised the possibility that the issue resided there: "I wonder if the brake light switch under the dashboard is the issue? I can see that the switch has two wires coming out of it. Is one for the left side and one for the right?" Adding that clarification to my answer... It's not the (brake light) switch. The two wires are not split like that. Both wires work both sides. If either side works, it's not the (brake light) switch. I'm just trying to save him the 23 bucks on the brake light switch he linked to at MSA. >> (link to the page here) << That's not what he needs. And in any event, I'm glad you guys are on it. He'll be fixed up in short order!

I'm back and had a few cycles to look into the EGR systems. Well guess what! They made a change in the thermal vacuum valve between 77 and 78. Short story is that (I would claim) they are interchangeable. Longer detailed story goes like this: The 77 TVV is a bang-bang digital switching device. Should be closed up to about 120F and stay open at any temp above that. (EC-11 and EC-12 of the 1977 FSM) The 78 TVV, on the other hand, is a more gradual opening device and it should also be closed up to about 120F and open above that, but there is a THIRD state for the 78 TVV where it will close again if it gets too hot. The 78 TVV will close at temps above about 200F, while the 77 version will stay open. (EC-11 of the 1978 FSM) Note, however, that in normal operation and a 180 degree F thermostat, the TVV should never see temps that high. This an overheated state. It seems that for whatever reason, they decided it was a good idea to cut off the EGR system if the engine got too hot. So as long as you don't overheat your engine, the 77 and 78 thermal vacuum valves should operate pretty much the same and be interchangeable.

It's not the switch. The two wires are not split like that. Both wires work both sides. If either side works, it's not the switch. I'd look for rust or corrosion inside the bulb socket.

Well I tested my original EFI temp sensor and my new replacement (with the offset tab) in a pot of water on the stove yesterday. The results are that I believe the replacement is close enough to the original to be considered a suitable replacement. I've got graphs and charts and numbers and stuff that I will post when I get more time, but unfortunately I'm headed out of town now and won't be able to get to it for a couple days. In the meantime, I can tell you that the sensor I bought was AIRTEX / WELLS5S1523 (SU4115). Interesting that the pics on rockauto don't have any tab, but the part I have definitely has the offset tab.

Yeah, it looks like the one I tagged was for 78. I don't know what the difference is, or if it matters. My instincts agree with yours in that it doesn't matter, but unfortunately I'm headed out of town now and won't be able to dig into it for a couple days. If you haven't figured it out, I'll investigate more when I get back. How many vacuum tube ports are (were?) there on your busted one? Two or three? The only thing I can think they would change would be a fine tune of the switching temperature. And if that's the case, I don't think you would care.

Haha!! Understood!

As it should be. The EGR runs off a ported vacuum source in the throttle body that is only active at a relatively low pedal position. Because of this, the EGR is only activated at "light cruise". It is completely disabled at both idle and anything beyond that light cruise position. In other words... The EGR is designed to incur no performance impact.

Haha!! Well SOMEONE had to ask, right? It could be BOTH, you know!!

Woah, I think my buddy paid less than $200 for his glass. Not sure if it was NOS sitting in a warehouse somewhere, or if someone is still making them new. But I'm positive he didn't pay anywhere near $600!

Am I sure? Not really, I guess. I bought one off rockauto a couple years ago because it was cheap and it came from the same location as something else I was buying so the shipping was free. If you look at rockauto, they have about ten different offerings for this sensor and some of them have the center tab, some have the offset tab, but most of them have no tab at all. The temperature curve would matter more to me than where the tab is. I'd just file the tab off and be happy. But if the temperature response is wrong... That would be an issue.

So, about that thermal switch thingie... Yes, it's all related to the EGR system. When the engine is cold, it blocks the vacuum to the rest of the system (thereby disabling it), and once the engine warms up, it will allow the rest of the system to operate. So, it depends on how much you care about the EGR system, but I can give you one other piece of data to help make your decision... Here's a replacement thermal vacuum switch on rockauto for $4.15. It's a mfgr close out. Buy two. https://www.rockauto.com/en/moreinfo.php?pk=3647541&cc=1209260

Oh, he's gonna make it. He has to bring me my brake booster!

Sweet. Glad that worked out. So, I've been meaning to ask... Is CRS your initials, or an acronym for a mental condition?

I wouldn't make any assumptions about the glass availability. A buddy of mine just replaced his this past winter and paid a very reasonable price for a brand new one. I don't remember the cost, but I do remember that I was surprised it was as low as it was. More expensive than a used one from a junkyard, I'm sure, but still way less than I would have expected for new.

Well that sucks. Did the shop that did the work at least acknowledge that they screwed up? You think that Z in the scrapyard has a drain plug?