Battery drain on Fuse 5

E28 technical advice asked and given! Troubleshooting, modifications and more.
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Zeuropa
Posts: 107
Joined: Mar 12, 2016 10:22 AM
Location: Denver, CO

Battery drain on Fuse 5

Post by Zeuropa »

Hello All,

Over the holiday break, I'm trying to fix some minor issues on my 'new to me' 533i. One of those issues is a slow battery drain that I've isolated to fuse #5. Of course that circuit runs a lot of different things on the car. I read in another thread that the Interior Light Relay can cause a drain, so last night I pulled the kick panel off to have a look. I think I know which one is the ILR because it makes, and I can even feel, the relay do its thang when I push/release the switch in the door jam. That said, the relay looks fine (the printing on the case is not faded/dusty), and the interior lights seem to work exactly as expected. Unfortunately, I can't seem to pull the relay out of its socket because it's way too tight and space is limited for my Trump-sized hands.

So before I break something trying to get it out (and create some new electrical gremlin), when these relays are the cause of a battery drain, do they still function as expected? If so, anyone have a tip for getting this thing out of its socket without inflicting collateral damage?

If a functioning ILR rules it out as the draining culprit, any other suggestions as to where to look to find the drain?
Could it be my old-style OBC? Mine doesn't work. It just flashes all the lights by the buttons. If I push one of the buttons, all the button lights stop flashing, but it doesn't function. All other systems in the car seem to work except maybe the maintenance lights in the cluster, but I think that's the cluster batteries.

Thanks to all for any assistance.
Zeuropa
Posts: 107
Joined: Mar 12, 2016 10:22 AM
Location: Denver, CO

Re: Battery drain on Fuse 5

Post by Zeuropa »

Update for the purposes of closure. I found my 60mA drain on fuse #5 - it was the instrument cluster. Also discovered that my OBC works just fine. When I had a PPI done on the car, the less-than-perfect shop told me that the OBC was dead - I shouldn't have taken their word for it, especially given all of the other things they overlooked, but I digress...
tschultz
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Location: Denver, Colorado
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Re: Battery drain on Fuse 5

Post by tschultz »

I've had a similar drain in my '88 535iA and I was suspecting cluster. What did you due to solve it-- remove batteries?
Zeuropa
Posts: 107
Joined: Mar 12, 2016 10:22 AM
Location: Denver, CO

Re: Battery drain on Fuse 5

Post by Zeuropa »

tschultz wrote: Jan 19, 2021 3:51 PM I've had a similar drain in my '88 535iA and I was suspecting cluster. What did you due to solve it-- remove batteries?
I haven't really solved it yet. Pulling the cluster out put the drain down to virtually zero, so I knew then it was the cluster. I had a spare cluster that I swapped in and it doesn't have a drain, but the SI doesn't reset in that cluster either. I've done an SI battery replacement in an E30, so I might do that or just put in a batteryless SI board.

Cheers
garageboy
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Joined: Feb 12, 2006 12:00 PM
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Re: Battery drain on Fuse 5

Post by garageboy »

Zeuropa wrote: Jan 19, 2021 4:11 PM
tschultz wrote: Jan 19, 2021 3:51 PM I've had a similar drain in my '88 535iA and I was suspecting cluster. What did you due to solve it-- remove batteries?
I haven't really solved it yet. Pulling the cluster out put the drain down to virtually zero, so I knew then it was the cluster. I had a spare cluster that I swapped in and it doesn't have a drain, but the SI doesn't reset in that cluster either. I've done an SI battery replacement in an E30, so I might do that or just put in a batteryless SI board.
For the cost of a 2-AA battery holder and some wire, you can make an external battery holder. I found that was the best solution. Cheapest. Functional.
Zeuropa
Posts: 107
Joined: Mar 12, 2016 10:22 AM
Location: Denver, CO

Re: Battery drain on Fuse 5

Post by Zeuropa »

Don't you hate it when people don't post a resolution to their own topics? Yeah, me too...
So, I ended up buying Ivo's battery-less SI replacement board, which 100% cured the voltage leak. I rebuilt the cluster with a mix of early 533i parts (kept the 325k odo for sure since that's a badge of honor), a later 535i cluster (I prefer the cleaner tach face), and some Euro indicator light panels. I put a piece of electrical tape over the SI lights since they don't function anymore. The tape worked out great - like the SI lights never existed. I also used 3m rubbing compound to polish out the scratches in the cluster plexiglass - that was a significant improvement too. I'm very pleased with the result. Now on to the next issue... But I don't need to worry about my battery going flat while I decide what that is.

I hope this helps someone.

Cheers,
Zeuropa
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