Captain Obvious

I can't wait! You know it's not going to run first try, right? You know that, right? I'm no expert on such things, but here's what I would do. 0) Make sure you have a fire extinguisher and a spotter/helper with you. 1) disable the fuel injection system and pull the spark plugs. Crank it over a bunch like that first. Just to get the oil circulating and listen for grossly incorrect noises, etc. To disable the FI system, I would disconnect the fusible link that runs to the positive battery post. And to look for oil pressure, you should be able to pull the oil cap on the valve cover and watch for oil coming out of the holes in the camshaft lobes as you (your helper/spotter) crank the engine. 2) Once you've got oil flowing, put a timing light on it and you might be able to get it spinning fast enough on the starter to get your ignition timing somewhat close to target. 3) Then once you've got oil flowing (and maybe timing close), pull the starter solenoid wire off and just hang on the key for a little bit and listen to the fuel pump running. I can hear the difference in sound of the pump when the load changes on a full pressurized rail. 4) Then once you've got oil, spark timing, and fuel... Put the plugs in, reconnect the starter solenoid wire on, reconnect the FI fusible link, cross your fingers... And give it a go. And call me so I can hear it running in the background!!!

LOL. I like it!! That's a great idea. So what is it that opens your garage door now though?

Cool. Things are better when the numbers line up. So it sounds like the needle heater can deal with 240mA on a pulse width modulated basis, but not forever. It's all about heat and average power.

Well that's what I get for relying on memory... I just took a quick look at a fuel gauge, and I got the heater resistances wrong. The heaters (both regulator and needle movement) resistances are about 50 Ohms each, not the 100 Ohms I mentioned above. The SENDER unit is 90-100 when empty, but the heaters in the gauge are about half that. If the regulator is closed, it will pull about 240mA. And if the fuel sender is at zero (full scale), the needle heater will pull another 240mA. So if you run the gauge without the regulator heater (no ground connected), the needle heater will see a constant 240mA at 100% duty cycle (not the 130 I mentioned above).

The gauge current will actually drop completely to zero when the regulator opens. You're looking at a wildly swinging PWM signal with the digital current meter on your power supply and I didn't see a zero fly by on the gauge, but it does actually cut off completely. And that comes back to the burn out the gauge question... In normal operation, the sender resistance could be zero. So in normal operation, the gauge heater will pass current proportional to it's heater resistance which is about 50 Ohms (which I believe is about 90-100 Ohms). But it doesn't pass that current 100% of the time. It's pulse width modulated and the average power is cut down because of that*. When you operate it without the regulator ground connected, it's running 240mA 130mA at a 100% duty cycle. And it sounds like given enough time, that's enough power to eventually heat up the nichrome wire to the point that it doesn't like it. *I didn't write anything down, but memory says the regulator runs at about 50% duty cycle once it's warmed up.

Glad to help. That temperature compensator/regulator is really an ingenious little detail. I should really put together that "how the gauges really work" thread I suggested some time ago. In fact, I suspect the OP's issue with his gauge is dirty contacts in the regulator portion of his fuel gauge. (But I haven't officially suggested that yet because it's jumping the gun until you work through the other possibilities.) So, you had previously mentioned (in another thread) the caution about damaging the gauge if you didn't connect the ground. That ground connection is the low side of the regulator heater, so if it's disconnected the PWM will run full bore 100% to the sender unit. But I'm surprised to hear it's enough power to burn out the sender heater. You've seen this happen? It's only about 240mA 130mA.

There will be some DC current draw variation due to the change in resistance of the sender unit, but the approx. once-per-second fluctuations in the current draw while you aren't changing the (simulated) sender resistance, that's not due to any divider. That's the temp/voltage regulator built into the switch. You're seeing the PWM draw from the regulator contacts opening and closing. You won't see this when you first hook up the gauge because the regulator is cold. And a cold regulator will run full bore (100% duty cycle) until it heats up.

My brake switch bumper turned to dust a couple years ago. Looked like this: So, I chucked up a piece of metal on the lathe and made this: Glued the little rubber pad into the recess and put it up under the dash. A completely unreasonable and unprofitable amount of time later, I have this: Next time, I'll use a quarter. With maybe a couple layers of hockey stick tape over it to prevent any metal-to-metal noises.

The only times I've messed with that spring and bracket was while I was bolting the throttle body onto the snout on the intake manifold, so I don't know if there's enough room to get in there and deal with it while the AFM and rubber tube are in place or not. You might have to take off that stuff in order to fit hands down in there to put the bracket and spring in place. Here's hoping you don't have to take too much off to get in there.

And here's a snippet showing where they originally connected the carbon can purge line:

1 - Yes, the vacuum port on the throttle body that points forward is the one that supplies vacuum to both the distributor advance and the carbon can "DIST" (distributor) port. From the throttle body nipple, to the "T". Then after the "T", one side goes to the distributor and the other side goes to the control signal port on the carbon can. 1a - Yes, if you aren't running EGR, just cap off the other vacuum nipple. 2 - The "purge" line on the carbon can goes directly to the intake manifold. One of the ports on top that is always straight-up manifold vacuum. 3 - The bracket for the return spring mounts under one of the four Allen head bolt that hold the throttle body to the intake manifold. As mentioned above, the bolt is the one on the lower right. Here's a pic of an upside-down throttle body and you can see where and how the bracket mounts:

The parts that don't look like they were plated... I think they missed the vats completely. Looking at the rest of the stuff, I don't think it's possible they went through the same process and came out looking like that. But glad they found the missing bits! That would have been no fun to replace all that!

I see what you did there.

No problem. I know this is in capable hands. I'll stand back some try to keep quiet.

We talked about it before (I think), but you have to be careful how you apply that formula to incandescent lamps due to the dramatic change in resistance as the filament heats up. For example, I just took a quick measurement off a little 3W inspection lamp bulb and got about six or seven Ohms cold. But for a 3W bulb like that, the resistance SHOULD be 48 Ohms. The trick is that it IS about 48 Ohms WHEN HOT, but at room temp, it's under ten. A couple of those in parallel like the dome light (because the door is open) and maybe the engine inspection lamp, or the map light in the console, or the .... Hope I'm adding value and not muddying the waters.

Steve, Backing up a little (in order to hopefully jump forward?). When you disconnect that four pin connector that goes out to the engine bay (the one with the R, RL, RY, GL wires)... The "short" goes away and the circuit under scrutiny goes OL. And on that connector, you have headlights, front marker lights, and the inspection lamp. All of those things are powered from the W/R wire feeding the fuse block. Either directly, or switched through the headlight switch. Can we please please get a double dog sure that the headlight switch is off?

I'm finding the wiring documentation for the early cars to be lacking and questionable. And not having a 240 here to look at for reference, it's tough. I particularly dislike the way they depicted the fuse block. Took me some time to figure out what (I think) is going on at there. And not showing where the connectors exist on the wiring diagram doesn't help troubleshooting any. And neither does wire colors magically changing along the runs. Anyway, might be old news for you 240 guys, but I came up with this: Note that if you flip the fuse block over and look at the wires colors there, some of them are different than what's shown on the wiring diagrams. I'm assuming the colors shown on the FSM wiring diagram are on the HARNESS side of the fuse block connectors and then didn't bother to list the colors that exist actually inside the block. Most of them line up with the wiring diagram, but some of them do not. Not having a 240 here for verification, I can't add much value. But I'll try to add a little.

Well I don't think I've gotten any wider since the last time you saw me! Haha! So the only thing hotter than the tarmac at that show was inside the big Quonset hut. It was shady, but like baking in an oven. Brutal. Your choice was either bake outside in the sun with a tiny bit of breeze, or bake in the three-sides-closed Quonset hut with no moving air at all. So Birmingham is likely to be like that, but with more humidity, right?

LOL! That was by design. I was looking for shade.

And as Captain Obvious, I'm compelled to point out that resistance readings like what you're taking are dependent on switch positions. By that, I mean... If something like your headlight switch is on, you'll read low resistance from the +12 volt side of the harness to ground, and it's perfectly normal. Same thing goes for the ignition switch. And the inspection lamp, etc. In other words... when you're taking resistance readings between hot and ground, you need to be double dog sure that all the accessories are off and the key is in the OFF position.

Everyone remember just how hot it was out there on the tarmac for the people's choice in Memphis? I went out for lunch with Blue @240260280 and Ms. Blue. We were trying to decide where to go and the answer was "Any place that has air conditioning. Oh... And eat slow!"

Not a very detailed list of which fusible link does what, but this should at least get you started:

And I would recommend that (since this whole thing started with an alternator replacement) you do your first fuse test with the alternator disconnected. Maybe the voltage regulator unplugged as well? If the low amperage fuse (or meter) survives that first step, then plug the voltage regulator in and try it again. And keep working in steps like that?

Steve has this well in hand, but let me just add a couple thoughts... In theory, that's exactly what the fusible link is supposed to do. It's supposed to cook and burn out before the wiring inside the harness cooks and burns out. The copper wire inside the fusible link is smaller than the wiring in the harness and it's intended to fry open before the wires inside the harnesses do. Point is... In theory, if the system was designed properly and fusible link did what it was supposed to do, then, in theory, rest of the wiring "should" be ok. In theory. Second thing is you said "when I attempt to reconnect the battery terminals, I get sparking that definitely does not look normal." - If you have an Ammeter with a 10A range, you could quantify the amount of that current before you get all worked up about the spark. By that, I mean... If you haven't measured the current, you don't really know if it's a problem or not. You could be chasing a non-problem. Maybe (just maybe) the spark WAS just a normal in-rush thing charging all the systems of the car and once that initial hit was gone, it may drop down to the milli-amp or micro-amp range? Connecting an Ammeter in series with the fusible link would give you an idea of how much current you're talking about. Half second ought to be enough for your meter to get a reading?