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i love cars just to get that out of the way! this was a 10 year anniversary gift, a 1974 450sl...it has 200k on it but was an arizona car and is immaculate! no rust, one owner...ok so the good part is out there lol...so i bought it knowing it had a new battery and alternator...well we drove it 1 mile to the local parts store to tighten the neg battery post...did that and went to leave and it died...jumped it and put it in gear and it died again. bought a battery from them as the one in the car read 1 volt. the alt read that it needed replaced. so charged old battery and it comes up good. bought a new alt and it tests good as well. the alt is not charging the battery tho. the battery light on the dash comes on. the original voltage regulator was disconected. when you pulll the positive off the post the car keeps running. i just cleaned up all of the connections at the battery and they were all rusty/corroded...hopefully that is the problem, but is there something i am missing? love reading all of the posts btw and plan on being a contributing member as long as we have this awesome car!
 

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thanks for all the help lol...it was just the battery posts that had corrosion and rust
 

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actually it wasnt! car is dead as a door nail again...it does have an after market sound system and an alarm...may try disconecting them and see if that may help? any other leads no pun intended...
 

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actually it wasnt! car is dead as a door nail again...it does have an after market sound system and an alarm...may try disconecting them and see if that may help? any other leads no pun intended...
Hi. I don't know if this will help . I had a 1979 450 SEL that was doing the same thing. I checked the drain on the battery with a multimeter that had the amp feature and found a circuit that was drawing about 4 amps with the key in the off position. These vintage cars used an electric motor in the climate control heater valve. Over time the seals begin to leak shorting out this motor causing the battery to discharge. I replaced that valve assembly and the problem was fixed. As a temporary fix ,while I was waiting for the part to arrive, I disconnected the valve wiring. You could pull the fuse but I'm not sure what else is on that circuit, your owners manual or the fuse list in the fuse box should tell you.
 

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thank you stude benz~! i did find a guy on youtube that shows many useful videos for these cars...in one of them he mentioned replacing all of the aluminum fuses with new ones...i plan on doing the battery draw trick as well and hopefully ill get to the bottom of this...bought the car about a month ago for my wife for our 10th anniversary and well that is today and she has yet to be able to enjoy it...
 

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i tested all of the original aluminum fuses and couldnt find a draw...so i replaced with all new brass fuses and still see a small draw each day it sits...any other info someone could point me towards?
 

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i tested all of the original aluminum fuses and couldnt find a draw...so i replaced with all new brass fuses and still see a small draw each day it sits...any other info someone could point me towards?
Hi. This won't solve your basic problem, but you could install a switch in the positive battery cable. These are meant to foil car thieves as the switch has a removable key. The switch would have to be turned on and off as you use the car. It would prevent the battery from going dead overnight at least so you could drive it while looking for the problem. Since your car is a 1974 model , it doesn't have all the computers newer cars have, so should not affect the drivability, as it would on newer vehicles, which would have to "relearn" settings for engine management. It would affect radio presets and the clock. Hope this helps a little.
 

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thank you...i have been so busy that i havnt had time to work on it...hope to this week
 

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I have a Hella kill switch in my Chevota, which I always wanted for a variety of reasons and it's lasted >20yrs. The super simple fix you may want to do, which I've done to most all my cars, is only put the batt terminals on hand tight so you can just twist to get it on and off. I hate having to get tools if I want to pull the batt or whatever so this works, which also works for pulling a terminal if I'm worried about a power drain.
A cleaner solution would be some relays between the batt and fusebox and your ign key turns on the relays. Basically an electric kill switch...
Other than that I'd be looking at that stereo and alarm.
Do you have a multi-meter? You can trace a drain down with those. I have several which were free from Harbor Freight tools. They used to give them out just to get you in the door, but point is you can get them pretty cheap, like <$10. Set to to AMPS, pull a fuse and put the two leads on the two spots where the fuse was, now it'll tell you if there's any current flow there. You can do the same with the battery, just pull a terminal and put one lead in the cable, other on the batt. Ideally, with the aformentioned hand tight terminals, you can put the leads on first, then remove the terminal. This way nothing loses power because some cars don't like that, but could also catch a drain that may only appear after a bit so this way you can catch it
 

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Still no luck :( I did find that the ballast resistors connections were not tight...i cleaned the connections with some sand paper and tightened them down...crossing fingers that was it...what a mess
 

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The ballast resistor wouldn't be it, but if it got looser it could've caused misfires and/or the eng just not running at all. Same with fuses, which won't drain power either, they just stop the flow when they get corroded just like battery terminals will. Aluminum corrodes pretty quick so it was good to get rid of those, but the part that holds the fuse may be alum too. Lots of old cars have that and the associated problems. The quick fix is it to twist the fuse so it breaks through the corrosion and makes contact again. Ideally you'd sand them and put a thin coat of silicone grease on which prevents corrosion for a long time. These days I don't think anyone uses Alum for fuses or holders so as far as I know it's just an old car thing.
So I'd get a multi-tester and track down that leak... It's obviously somewhere so it can be found. If for example its the stereo, or whatever, and cannot be fixed, you can put a relay in so it's turned off when the key is off. Not too hard imo but gotta find the leak first...
Something I thought I'd also mention, which I've done with cars that will be sitting for long periods so battery drain is an issue; is put a trickle charger on it or get a solar charger. Not a fix but it keeps the batt charged because they don't like being discharged. So basically car batteries do not like to actually be used, and more you discharge them the harder is it on them. So I hope you're not letting it drain then charging it. Instead keep it topped off with a charger or disconnect it. I have a solar charger I got from Harbor Freight that plugs into the cig lighter, which is nice and easy, no extension cords, you just have to be sure the cig lighter is powered when the key is off. Then I just put the charger on the dash to collect sunlight. If in a garage then you'd need a regular charger of course. I'd pass on any "smart" chargers, which usually don't last long at all, if they work in the first place. A cheap old $10 charger works like a champ.
 

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Ok thanks for the response! I truly appreciate it...ill try the meter method once more...maybe I'm not doing it correctly but I've tried a meter and a test light and got nothing...should be simple process but I have never done it before so I guess I better try again lol
 

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So power is going through a fuse (we assume), so pull the fuse. Now put the multimeter on the two contact points the fuse was in so now the power will flow thru your meter. If you've never used a multimeter then there may be a learning curve.
A test light should work too because the power that was going thru the fuse will not go thru the light and should light it up, but not always...
If you're new to multimeters post a pix of it and I'll help
 

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I am kinda new to multimeters...but I put the black on common and the red on the 10 amp setting...should be good?
 

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Ok I'm a mess now...thought I was doing good by cleaning up some connections last night...the car won't even start now...could I have put a ballast resistor on backwards? It has 2 of them...if I did put it on backwards coukd I have fried it?
 
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