I’ve acquired a classic 1977 124 Spider that hasn’t seen much action in ~1 decade. I’ve had it ~1 week & the most important stuff works. I’ve done a number of small trips around town. Yesterday in the garage I wanted to catalog everything that needs repair by flipping all knobs/switches and marking what’s not working. I found that the wipers don’t work (but the wiper fluid pump does) and the cabin air/defrost fan doesn’t come on, and one of the air levers is locked/frozen. I left the car for a couple of hours and when I returned I thought I could smell plastic burning. I hunted for the smell & found a small electronic component under the hood that seemed like it might be hot, but I wasn’t sure. I left the car overnight with the hood up and when I returned I the smell was gone but the battery was dead!
I figured I must have left something on by mistake so I went through all knobs/controls using the owner’s manual to make certain that everything off (it was). Then I jumped the car & drove it around for ~20 minutes. Left it in the garage ~1 hour being very careful that the doors were closed, no lights were on, etc. & checked on it to see if the burning smell returned (it hadn’t). Left it overnight & in the morning it was dead again!
I don’t think that there’s anything wrong with the battery or alternator because it had run fine all week with multiple short trips around town. I think it’s more likely that an electrical component is shorting somewhere & draining the battery. Perhaps turning knobs & flipping switches pushed an old brittle electrical part over the edge?
My question is: what is the best way to find the malfunctioning electrical component? I was thinking of the following:
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Jump the car & recharge battery by driving around town
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Park in the garage and disconnect all fuses
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Return every ~8 hours and check the battery, if it looks OK then replace a fuse
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Repeat the above step until the battery dies
Using that approach I can isolate the bad component to the circuit running through that fuse. It’s a slow process though, is there a faster or more efficient way to do this? Any other ideas as to root cause? Any thoughts appreciated, thanks!
If it drains when the battery is off then you can only look at fuses that are always on. Pull half of them, see if it’s gone. If it’s not then pull the other half and see if it’s still there. Then each time only put back half as many fuses as you pulled out. It’s a 1977 so there can’t be that many of them.