Electrical issues - mostly relays - BMW Forum - BimmerWerkz.com
3-Series (E21, E30) Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.

 
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#1 (permalink) Old 01-12-2012, 06:56 PM
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Electrical issues - mostly relays


Hi guys, newly registered user, female mechanic, and semi-proud owner of a 1987 325 2-door (semi-proud because it's currently chocolate brown until I can scrape up enough dough to give her a decent paint job.)

Lately I've been having a few electrical problems, which I expect being the owner of a 25-year old car. The 325 was a trade-off with my dad for a 97 Dodge RamVan, in my eyes I got the better deal My problems started with the headlight relay, which was replaced. Everything was going fine until the drive home from work yesterday. I stopped to fill up at a station not too far from work, so the car hadn't had time to fully warm up. After filling up it wouldn't start. We narrowed it down to fuel delivery. I thought it was the cold start injector or coolant temp switch/sensor but both tested ok.

Here's where things get weird. The #11 fuse would test for continuity when out of the fuse box, but when it was in the panel it wouldn't pass voltage with the ignition engaged. The socket for the fuse passed voltage with the ignition engaged. The socket wasn't dirty or damaged. We tried different fuses and ended up jumping off the #10 fuse just to get it out of the gas station parking lot.

Once at my dad's house, I swapped the fuel pump relay with the low beam relay as a test, and it started and ran just fine. Not wanting to drive home with no headlights in the dark, I put the low beam relay back in and instead used the high beam relay for the fuel pump. I turned the low beams on to make sure everything was back in order, and everything worked. When I left for the day, I noticed my headlights (low beams) don't work again and I had to drive home (45 minute drive) with the brights on...and pissed off a few people, I'm sure. I just tried the fog lamp relay, the high beam relay (hey, they worked on the way home) and the oxygen sensor relay - all of which I know work. The odd thing is, the relay for the fuel pump wouldn't run the pump but it will run my high beams.

I did order 2 new relays today, so hopefully this is just some weird fluke that will be fixed with two brand new relays, but I won't know until they get here and I'd really like to drive my 325 instead of my husbands Dakota. We have a long commute to work and I'd rather drive the vehicle that gets the better fuel mileage.

I'm at a loss. I'm fairly certain the bulbs aren't blown, but that could very well be the case. I didn't check the fuses for the low beams because I left my multimeter at work, but what are the odds that both of the fuses go at the same time?

Any suggestions would be greatly appreciated.
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#2 (permalink) Old 01-13-2012, 02:23 AM
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Welcome to the Werkz.

Did you try replacing the #11 fuse, maybe it was making contact when out of the fuse box because it wasn't twisted or under some sort of physical strain?

Is there a common upstream fusible link that could be gone?
A multimeter will make all this testing a lot easier, (but you alreadyknow that).

Test your bulbs by disconnecting the lead and connecting 12 volts directly to one of the bulb's pin and a ground wire to the other pin. Its unusual to have several things go wrong simultaneously without something in common, or if you've disrupted something else in the diagnosis work that you've done? How long will it take for the new relays to show up?


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#3 (permalink) Old 01-13-2012, 06:46 AM
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Thanks for the reply.

I tried a different fuse in the #11 spot but nothing worked until I swapped relays. I know it's a weird issue, but I also know that BMW's have strange electrical issues by nature. I'm pretty sure the reason it wasn't passing current was due to the faulty relay, once I swapped it out for the high-beam relay the pump works fine. It just doesn't make sense that my low-beams don't work because that's not the relay I'm using and I tried other relays that I know work perfectly. It is plausible that during all this switching around that something like dirt or oil got up into the contacts, but on 3 different relays? Stranger things have happened...

I am going to test the rest of the chain down to the bulbs themselves, it was dark when I got home and I didn't bring my multimeter. I'm not sure when the new relays will be here, I'm kinda hoping they will show up today. I ordered them from AZ Autohaus yesterday, they're in NC and I'm in SC so if I got them ordered in time and they shipped yesterday I'll see them today.

I won't be able to check anything out until Sunday anyway because we're going out of town.

Crossing fingers.
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#4 (permalink) Old 01-13-2012, 07:25 AM
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I have friends in SC (near Simpsonville). I was over there 5.5 years ago, stayed there, Myrtle Beach, Atlanta. People are really friendly there, but they had trouble with the accent, or maybe I just speak to fast.
Good luck with it all.


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#5 (permalink) Old 01-13-2012, 05:22 PM
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this may not be to much help but are relays wired the same configuration,the prongs are the same the terminals may corespond to differnt conections
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#6 (permalink) Old 01-15-2012, 05:50 PM
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That's what I'm thinking. I was talking it over with my dad, the oddity of one relay working for something (fuel pump) and not working for something else (headlights.) It's quite possible that different components use different terminals on the same relay.

I thought the parts might come in tomorrow...no luck, it's a holiday and UPS won't deliver. I guess I'll have my answer on Tuesday.

Thanks guys!
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#7 (permalink) Old 02-16-2012, 01:08 PM
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After ordering the wrong relays, and the company letting me return them and swap them for the correct ones (really appreciative of that, normally electronic parts are non-refundable), I figured out where I went wrong. The relay I temporarily used for the fuel pump came from the high-beams, because I figured that for the drive home I wouldn't really need my high-beams. The fuel pump relay is 4prong and the high-beams is 5prong, but at some point in the last 25 years the socket for the fuel pump had the center leg punched out so the 5prong relay fit. I kinda freaked out when the relays got here the second time and I went to install the one for the fuel pump and saw the 5th prong, but after looking closer at the socket I realized that there's no contacts in that center slot. The baffling thing is that the high-beams worked fine with a 4prong relay and not having that center leg made the low-beams not work. I'm guessing that 5th leg carries current to the next relay in line, that's the only logical reason I can think that the lights wouldn't work...

I was getting kinda upset when I got home with the new parts that night because when I installed the headlight relay nothing happened...no lights. It wasn't until the next day, when I could really see what was going on with all the different relays and sockets that I realized what I'd done.

Over-engineered. But I won't trade it for anything. I love my chocolate bomber.
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#8 (permalink) Old 02-18-2012, 09:57 PM
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Quite often the same relay socket is used for a variety of applications, it does however as you have discovered form a trap for the unwary. The good thing is that CB is back on the road and doing what its supposed to be doing. Well done.


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#9 (permalink) Old 02-28-2012, 02:57 PM
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Okay...

After 2 weeks, the headlight relay has already gone bad, and I have a feeling that the FP relay is also going (it's getting harder to start, which is how this all began.) I put a bigger (40a) relay in the headlight slot and it's been working fine so far. Does anyone have a suggestion on where to start checking things out? I knew the electrical system is going to suck, it's a 25-yr old German car. So far the only problems I'm having have been with the FP and the lights (the p/s window has issues, but it's a short in the wiring inside the door, I just haven't permanently fixed it yet.) I just don't even know where to begin as far as checking point to point on the electrical delivery. I do have a good mechanic (my brother) who can help me, but he's more of an American car kinda guy.

Thanks guys.
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