Relays in the '74 electrical circuits

Bmachine

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Actually, I do not. I wasn’t sure if this was related to this relay issue or with something else. But I’m not sure what else it could be since I haven’t done any change to the electrical circuit.
 

HB Chris

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Bo, Without a relay you will have no hi beams and your relay is MIA. You can wire it to function as a pre 74 would with a standard relay and I could walk you through it.
 

Bmachine

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That sounds great Chris. I do not have fog lights because I have never found them to be of any use with any of the cars I have driven. And we get a LOT of fog where I live. So I am totally open to getting rid of that option.
 

sfdon

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I know nothing about that relay- use your horn relay in that spot and see if highbeams work
 

Bmachine

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For the sake of completeness, here is an earlier thread which also has info on this subject:

 

Bmachine

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Chris, apologies for not having replied to your questions earlier. Too many loose ends to be tied in a short time...

Bo -- You probably know this, but the toggle feature of the fog lights is to meet federal regulations as to how many lights you can have illuminated facing forward at any one time.
I actually did not know that. Good info.
-- As Chris notes, the relay hanging where the voltage regulator had been in the older cars looks like a modification to your car based on the screw and nut used to hold it in place. My guess would be that this was done to allow for the use of a newer relay.
It is definitely part of the original wiring. HB Chris originally thought it was Hi Beams but we now know it is not.
-- If the connection to the flying relay mount in your eighth picture is function, is some type of hack fix. It is not a safe connection with this much of the connector exposed. Moreover, that type of spade connector is designed to snap into place once connected so as to prevent it slipping out of place. You would not use that type of permanent connector on a relay mount because you have to mess up the connector, and possibly the relay mount, if ever you needed to change it. And, of course, that type of relay mount is intended to be fitted into a sheet metal slot somewhere.
According to HB Chris and sfDon it is the automatic starter relay. I believe Peter C said in another thread that it needs to be "jumped" for a manual tranny car and that is probably what that wire is doing. Albeit very poorly indeed...
-- The connector with the two black wires laying loose in your last picture needs a home. It is difficult to see the connector, but it looks like one of those female connector that mates up to an opaque white connector.
Right. Still a mystery wire.
Are you trying to fix something specific?
Yes. There are a fe2w things that are not working. Hi Beams, horn. But also trying to clean things up down there.
 

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Bmachine

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The relay where the regulator belongs is hi beam, remove relay and see if hi beams can flash. Hi beam is white. Relay in middle is horn, unplug and test, green/yellow, brown/yellow, red, black. Forward most relay looks like A/C relay which you stated, I wonder if all 74s have one there, that’s a new one for me at least.
Yesterday my friend Gary and I looked into this on his '74. Sure enough, his car also has that mystery "hanging relay" dangling under the voltage regulator. (I moved it up where the reg used to be on that first photo). This is now the third '74 which has this very strange floating relay (@Sven had reported the same in July 2016). We decided to remove it to see what happened. Sure enough, that killed the high beams! So, as Chris suspected above, that is indeed the High beams even though the diagram shows the high beams going to the Fog relay. So either that diagram is not entirely correct or it is not the right one for those cars.
But stranger things were still to come: On his car, removing the Fog relay killed both low and high beams with only the high filament of the outer light coming on when the High beam stock was activated. On my car, there is no Fog relay to begin with, but my low beams work and high beams do not. I first thought that this meant that my (newly identified) High Beans relay was dead. But strangely on Gary's, removing that Fog one caused a very different reaction. (Unfortunately my car is away and I wont be able to replace my bigh beams until possibly tomorrow.)
I am starting to think that these two relays (Fog and High) have a very symbiotic relationship and that they both need to be present and working correctly for things to operate normally.
 

HB Chris

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Bo, what happens when you move the horn relay to the spot for the fog relay? That is the one with one red and two white, correct? Everything should work. I have a spare relay when I see you tomorrow.
 

Bmachine

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I did try that but the highbeams still did not work. Low beams where unaffected. Which makes me believe that you need both the fog relay and the highbeam relay to be working correctly.
 

HB Chris

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I have spare relays for you. Interesting that the wiring diagram appears to show only one relay and it is labeled fog but you can see the wires to the hi beams as well.
 

Bmachine

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FYI I did try Chris’ good part in my “dangling ‘74 relay” and all of a sudden my high beams came back to life after however many years on the DL list...
 

Ohmess

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Bo -- when fog lights are installed, power for the high beam runs through the fog relay. If the fog lights are not switched on, power goes from the fog relay to the high beam relay. If the fog lights are switched on, the fog relay toggles off the power to the high beams and sends it to the fog lights. Again, this is to comply with US federal requirements on how many lights can be illuminated on the front of the car above a certain wattage.
 

Bmachine

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Yes indeed, Chris. The makes sense.

What makes less sense is that no cars came factory with fog lights and yet, the fogs have a properly installed and secured relay while all cars came with high beams and yet, those just got some dangling appendage left hanging loose under the regulator. Granted, this was a late change for '74 and 75 but it still feels unlike what BMW would normally do.
 

Willem Tell

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Bo -- when fog lights are installed, power for the high beam runs through the fog relay.
HB Chris' and Ohmess' descriptions are correct, (HB Chris explained it to me! ;)) however it might be more accurate to say that the power for the high beam runs to the fog light relay (socket). The fog light relay socket lug #85 is a tie-point for the high beam, therefore no relay is necessary in that socket for the high beam to work; the power is simply passing through the lug on its way to the high beam lights. (I have no relay in that socket, and my high beams work.)

You normally have power to the low beams from the light switch to the fog light relay (coil #85) under the dash ( low beam relay in HB Chris' great photo, and less confusing description) (yellow #30) to fuses 3 & 4. When low beams are ON, power from fuse 4 (purple/yellow) goes to the fog light switch and then onward as the (green) wire to the fog light relay by the battery.

If you have a relay in the socket (and fog lights installed), and you press the fog light switch on the panel under the steering column, you get power to the fog relay coil #86. The relay contacts close and connect battery (red #30) to (yellow #87) and the fog lights come on.

If you now turn your high beams on, the (white #85) from the high beam switch applies power to the other side of the fog light coil, so there is +12V on both sides of the coil and it releases, turning off the fog lights. when you turn off the high beams, the relay engages again and your fog lights come back on.

That mystery hanging relay may have been added to replace the one under the dash, or maybe an attempt to run the high beams through a relay? (a desirable modification)

66271


Since I have no plans for fog lights, I am planning to modify the fog light relay to act as a high beam relay to spare the high beam switch the high current draw:
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It will still look "stock" and I won't need an extra relay in that area. I will beef up the thin little wires to the high beams when I make this mod.
 
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Bmachine

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Thanks Willem. As I mentioned earlier, this "dangling relay" is not a modification but is part of the factory wiring for this model year. When all relays are properly installed and working, it functions quite well in a manner similar to what you describe, without having to make any modifications.
 

Willem Tell

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Interesting. I realized after going back to the beginning of the thread that you had pretty much nailed the description already.
 
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