1978 Oldsmobile Toronado XS

Never mind. The solution was so $@% simple that I feel like an idiot. I had the front doors open because I'm letting the interior air out, as I've mentioned. Well, the circuit through all the lights that go on when the door jamb switches are closed is enough to cause continuity across the battery leads. As soon as I fully closed both doors, bingo, no more short circuit. Should have thought of this right off the bat.

The car also has a clock, which runs continuously and is thus a constant draw on the battery, but apparently there's enough resistance through it that it doesn't cause a short circuit to appear. Either that or it's not hooked up, but I have no reason to believe it's not.

 

If you ever have a battery draw-down, it's really simple: disconnect the neg, charge up the battery, and hook a headlamp in series between the post and cable terminal. If it's a dead short, the lamp will be bright; if it's dim to fairly bright, it's a load that's 'on,' like the interior light or the ignition is on for whatever reason (had a gal bring in her Pontiac 6000 claiming the battery was dead, which it was, but when she'd try to start it, it wouldn't--I found out the bolts holding the ignition electrical switch were down in the lower dash shroud, and as she turned the key, the switch would go back and forth, stuck in the ON position). As that lamp is on, you pull fuses and disconnect the alternator to find which circuit has the problem, then chase it down.

 

Thanks for the tip!

 

To finish the fuel pump story on this, I finally got the correct part from Amazon today. It's an Airtex unit. I put it in the car, put in new rubber lines from the pump to the steel lines, put 3 gallons of gas in the tank, and gave it a go. It started easily and sounded good. I had replaced the plugs and wires earlier, and I connected a new battery today as well. It was nice to see things like dome lights, the radio, the gas gauge, the clock, and the idiot lights all light up for the first time in probably a decade. Three of the four headlights went on. Even the power antenna went up and down when I turned the radio on and off. One issue I'm apparently facing is the heater/AC blower motor. I moved the lever from OFF to VENT, put the fan speed up a couple of notches, I heard it spin maybe two revolutions, and then it died. Ah well.

Another issue is a fuel leak at the rear of the car. I inspected the rubber lines coming off the top of the tank and connecting to the steel lines (there are three) as best I could, and they looked OK, so that's why I went ahead and put gas in the tank to try to start the car, rather than doing a more thorough job with the fuel system at the rear end. But the leak is pretty significant, so I'm guessing a bad rubber line somewhere. I will have to drop the tank. I don't think it's the tank itself because the leak stops once the engine is off, so I don't think there is a leak in a tank seam or something like that. Plus, with only three gallons in the tank, I don't think there's enough gas to even reach the level of the seams. Also, the tank is wet above the seam, anyway, suggesting a leak at the top of the tank.

Another thing is that the GEN light glows dim when the engine is running. The alternator is as old as the hills, but I put a voltmeter across the battery terminals while the car was running, and it read over 14 volts, which I think is what it should be. I noticed that the alternator belt has a little more play in it than it should, so maybe it's just a slightly loose belt. That's the next thing to check.

 

The belt may need to be snugged, but if the GEN light is still glowing, it's likely a bad diode bridge. You should still be able to replace it yourself, if you can find a bridge at a NAPA or a Carquest, or if there's a local rebuilder. We have one or two left in greater Seattle ourselves.

 

Thanks for the tip. If you don't mind a dumb question, is this diode bridge something that's attached to the alternator, or is it elsewhere under the hood? Can you point to a picture of one? Thanks.

 

NAPA shows something called a "diode trio". Is this what you're talking about?

https://www.napaonline.com/en/p/ECHAD1206?searchCategory=11.2&searchIndex=App

 

I just now checked the service manual, and, yes, there is a part inside called "diode trio." Looks simple enough to replace. There is a step-by-step troubleshooting sequence in the manual for when the GEN light glows dimly with the engine running. The first suggestion is check belt tension. The second is to make sure the red wire connected to the BAT terminal is tight. The third is to make sure that both red wires at the generator show battery voltage. If all three of these are met and the GEN light still glows, the procedure moves on and gets a bit more involved. In one case, the solution is to ultimately replace the diode trio or the rectifier bridge. Given that diode trios are about $6 at NAPA while rectifiers are about $40, I'm hoping that, if I have to replace one of them, it's the diode trio.

 

The alternator should be a 10SI, so all controls are internal. I would pull the two out and do a diode check on each diode to determine if any have gone bad.

 

You can pull it and have it tested; the price of $46 for both parts is fairly cheap, versus a reman for 2-3 times that price.

 

All the diode trio does isensure current flow goes to the bridge, not from. The rectifier is what converts A/C voltage to D/C voltage, and when a diode goes out, it causes A/C voltage to 'leak' into the car's electrical system.

 

BTW, I just remembered you said you have a shop manual....

 

The alternator is definitely a Delco-Remy as it says that on the back. I will do some checking on it as soon as I finish the current project, which is replacing the rear rubber fuel lines. Unfortunately, to get at the ends of them (there are three) that connect to the sending unit, the tank has to be lowered. All three lines are old and stiff, and one of them has a big hole in it.

 

Yes, I do have the chassis service manual, and there is an extensive troubleshooting section for when the GEN light glows dim with the engine running as I mentioned earlier.

 

FYI every time I tried to save a few dollars and replace just the diodes on an Alternator it usually worked for a few weeks then something else would go on the Alt (usually a bushing). Now on my old cars I just take electrical parts to a rebuilder and have them gone thru completely. Usually don't have any issues with them after that.

But it does usually cost about $100. And you keep your date coded part if that is important to you.

Good luck if you decide to tackle it. It is not that difficult if I could do it as a teenager you should be able to do it.