74 light wiring vs pre 74

[rsporsche]

i was looking at the 74 wiring diagram for lighting vs. the 2800 cs / 3.0 cs (USA) and i have a question or two.

first comment - i am not great with automotive electrical - the basics sure ... i have already added the direct power to the low beams with a new relay as that is simple enough - the headlight switch sends power to the low beams. where i am going with this is trying to introduce a fog light circuit. it seems simple enough to send power from a fuse to a new switch (probably fuse #6 since it in no longer directly powering the low beams), add a ground for the new switch and once pressed, continue the power to a new relay (pin 86). of course, pin 30 would have a new fused power direct from the battery, pin 85 would go to ground and pin 87 would send power to the fogs. The new switch on the underdash panel (like the rear window defrost button). i could ignore the #15 connector and not worry about the high beams / fogs being on at the same time.

we will start with what is most common to most of us - the pre '74 diagram - #18 is the horn relay and #16 is the high beam relay (#15 is the foglight connector, which should shut off the fogs when the high beams are on) - no fog lights are shown on the diagram. here power is fed from the battery to pin 30. pin 86 ties to the dip switch (white wire) and also feeds the foglight connector (if the dip switch is activated, it would send power to the fog light connector. pin 85 ties to ground and to the program tester (#31 - brown wire) and pin 87 powers the high beams. so the question is if i wanted to be 'correct' and tie in the #15 connector ... which relay pin would it tie to? (presumably 85 on the fog light relay)

this is the 74 diagram - #16 is the horn relay and #15 is the fog light relay ... although the high beams are tied to it. the high beam / fogs use pin 30 on the relay to power the lights (red wire direct from battery). pin 86 on the 74 ties to the fog light switch, pin 85 ties to the high beams + the dip switch and pin 87 ties to the fog lights. the fog light relay is not grounded, it feeds fogs or high beams when one of the 2 switches is activated. the ground has been removed from the relay - both the fogs and the high beams are directly grounded and the program tester ground has been relocated.

the either / or approach of fogs / high beams approach in the 74 wiring seems like a more elegant way to implement fogs - UNLESS you want to be able to run all lights at the same time. so here's the part i don't understand about this relay configuration - in the 74, the default has pin 85 powered (high beam wiring) which also connects to the dip switch ... which is open unless the switch is used + powers the high beams - not sure how this works or if it would only work with the 74 switch. if the fog light switch is pressed, it energizes pin 86 an and sends power to the fog lights, turning the high beams off. if the dip switch is toggled, it cuts off power to the fogs. if neither is toggled, how does the circuit deal with the power ... i don't understand the lack of ground default. for those of you who are less electrically challenged than me, i would appreciate knowing how does this resolve itself?

 

[HB Chris]

I think Don understands this. In the 74 the high beam when activated cuts off the fog light. I would rather use all lights if needed.

 

[rsporsche]

yes, i tend to agree with you - i will just leave the #15 connector just like its been for the last 54 years - empty. and just make the push switch very simple - on or off. i will do another fused big wire to the relay (mounted behind the grille or under the other relays) ...

the one thing i found odd when looking at the low beam relay on the 74 - the wires go thru the fusebox on the way to the lights - presumably the relay is next to the fusebox. i like it next to the battery with a big wire feeding the lights with an inline waterproof fuse (thanks Don).

 

[e9Leveque]

It seems like this may be a circumstance for using a relay with an 87A that allows for one leg to always be open and for the switch closure to swap between them? Having just done my rear window motor upgrade and having to figure out adding two relays when changing the 3-wire to 2-wire motors, the wiring diagram that I initially encountered didn't work out, as it would only power one leg but not ground the other. The diagram pictured below did work, as it used the 87A to have a normally open connection to ground on both relays, and then pushing the switch up (or down) powered only that relay while leaving the other grounded (ignore the red circles and the diodes, they aren't the necessary part). Could the same concept work here? The diagram you have above has standard SPST relays which could be swapped for a SPDT relay.

 

[e9Leveque]

Secondarily, as I have been adding these additional circuits wired directly to the battery, I have been adding the connections directly at the battery. Is this what everyone is doing? I have a battery terminal that has space for additional connections to it, but it just looks a bit odd having 4 or 5 separate red cables coming off the battery each with its own 30-A fuse wired into it. I guess I could create a small little additional fusebox in the engine bay for these - power to rear motors, power to amp/sub, power to low beams, etc, unless someone has a better option.

 

[rsporsche]

Possibly, i haven't dealt with any 5 prong relays. one quick question in your diagram - shouldn't red power generally come into #30? perhaps relays work backwards, i dunno.
i have attached a schematic for wiring the sardine motors with a direct power wire. the one thing i left out of my schematic is that the green wire running from the fusebox to the switch has to remain to power the relay when switch is pressed

i was going to run a single large wire from the battery into the interior to a fused block - and distribute to each side and each motor relay - running 4 big wires will be harder to get thru the firewall

 

[e9Leveque]

Correct, the red power normally attaches to 30, and when I first looked at this diagram I thought it was wrong. BUT, yes, the relays work backwards, and in following through the wiring it makes sense why it's wired in reverse since in this circumstance the two wires to the motors need to swap power and ground depending on whether the switch is pushed up or down. I needed to wrap my brain around that, but can confirm that it works as shown. For your circuit, you shouldn't need two separate relays, but using the SPDT will switch power between 87 or 87A. Imagine it as a light switch where when pushed up the power is going to 87 powering one light (red) and then when it is in down position it powers 87A going to another light (green) rather than just having the light off. So one light is always on but never both (or neither). Your circuit would have a switch in the dash which is powering this whole relay on/off while the fog light switch would swap between high beam (87) or fog light (87A), since presumably one wouldn't tend to have both on at the same time.
Regarding your diagram for the sardine motors, that diagram works for the 3-wire motors, where there is a continuous ground and the power either needs to go to green wire (up) or black wire (down). The 2-wire motors don't have a static ground - when up one wire is power and the other ground while when down they swap roles. That was the challenge. The various threads on this tend to blend "adding relays to motors" and "converting from 3-wire to 2-wire motors" - each half of that change requires its own version of wiring. Maybe at some point I'll gather all of these diagrams into one thread so it makes the job easier for the next person.
For the fused block, looks like there are various options available on Amazon, some even with slots pre-wired to accept 4-pin or 5-pin Bosch-style relays, which is pretty nice. I may order one or two to see how they look in real life. Some have extra slots for fused non-relay runs (like the amp/sub, for example) and other fuse slots specifically routed to the relays. Theoretically because the slots are just holders for the relay, it shouldn't matter whether you use 4-pin or 5-pin relays since the switching all happens in the relay. To add to the complexity, for my low beams I was planning to use one relay with a double-87 so that I can just have left and right side coming right off the relay - it's a 5-pin wherein there are two 87s, both of which are powered by 30 when the switch is closed.

 

[rsporsche]

i have always heard that with sardine motors (3 wire) that you need 2 relays. maybe you wouldn't with a 5 prong relay. my understanding is that with power to 30 you get a signal when pressing the switch and that initiates the relay on pin 86 - as long as you hold the switch down, the relay will have the motor turn. the problem is the up signal -

 

[e9Leveque]

Both the 3-wire and 2-wire need two relays, unfortunately. Maybe there is some relay out there that does some internal switching based on receiving a positive input down pin 85 vs 86 but no one had discussed that and my understanding of relays is rudimentary. You're correct that the switch press leads to a connection from switch (86) to ground (85) which then opens the circuit to allow power to flow between 30 and 87. Since the electricity is effectively bidirectional, 85 and 86 are interchangeable as are 30 and 87. In the 2-wire motor circuit, the reason for the swap between 30 and 87 is that attaching the power to 87 makes the power INPUT switched on by the 85-86 connection rather than the power OUTPUT being switched. This I believe is a somewhat unusual requirement and again in this case is due to the fact that the 2-wire motor swaps roles for the two wires depending on switch up or down.
Going back to your need here though, I would think that the option I mentioned above with a 5-pin relay with 87/87A would work to switch power between high beam or fog lights.

 

[HB Chris]

Scott, 74 low beam relay is above hood release handle. I don’t add fuses to relay by the battery.

 

[ScottAndrews]

You probably want to avoid powering the fog lamps directly from the fog lamp switch since they draw a fair amount of current. So using a relay for that is a better option.

If you wanted to use a fog light cutout relay, you could wire it like this.

Here the fog lamp switch energizes the fog lamp relay (via pin 86). This closes the contact between pin 30 and pin 87.
Pin 30 is connected to pin 30 of the cutout relay.
Pin 87 a of the cutout relay is normally connected ted to pin 30 of that relay, so current flows into pin 30 and out of pin 87a to the fog lamps.

Connector 15 goes to pin 86 of the cutout relay.
If the high beams are on, then Connector 15 is energized (per your diagram), so the cutout relay switches form connecting pin 30 to pin 87a to connecting pin 30 to pin 87.

Since 87a is no longer connected to pin 30, there is no current to the fog lamps, and they go off.

You can also wire this using "negative logic" so the fog lamp switch would close to ground. In that case pin 85 of the fog lamp relay would connect to the Fog lamp switch, and pin 86 would connect to the fog lamp fuse. Closing the fog lamp switch woudl then ground pin 85 causing the relay to close, and the above sequence woudl then apply. Like this:

This approach is actually more convenient since you can still fuse the fog lamp circuit, but you do not need to run a wire from the fuse box to the switch. Instead you just write one side of the switch to a convenient ground.

HTH
Scott

 

[ScottAndrews]

Deleted

 

[ScottAndrews]

...the fog light relay is not grounded, it feeds fogs or high beams when one of the 2 switches is activated. the ground has been removed from the relay - both the fogs and the high beams are directly grounded and the program tester ground has been relocated.




the either / or approach of fogs / high beams approach in the 74 wiring seems like a more elegant way to implement fogs - UNLESS you want to be able to run all lights at the same time. so here's the part i don't understand about this relay configuration - in the 74, the default has pin 85 powered (high beam wiring) which also connects to the dip switch ... which is open unless the switch is used + powers the high beams - not sure how this works or if it would only work with the 74 switch. if the fog light switch is pressed, it energizes pin 86 an and sends power to the fog lights, turning the high beams off. if the dip switch is toggled, it cuts off power to the fogs. if neither is toggled, how does the circuit deal with the power ... i don't understand the lack of ground default. for those of you who are less electrically challenged than me, i would appreciate knowing how does this resolve itself?

Your initial description is a bit hard to follow. The fog lamp relay will only close when current flows through the coil (pins 85 and 86), so it MUST have a ground path.

I am not sure how the high beams come on, since that part of the diagram was not included in your post, but is clear that when the high beams are ON, pin 85 of the fog lamp relay will be energized. If pin 86 is energized the relay will not close (so pin 87 will not be energized), because the relay coil will be energized at both ends, so no current will flow through the coil.

When the high beams are OFF pin 85 is not energized, BUT remember the high beam filaments are still connected to pin 85, and they provide a path to ground for the relay coil current if pin 86 is energized. This current is small, and thus it is insufficient to illuminate the high beam filaments.

So:
When the high beams are OFF and the fog lamp switch is ON, Pin 86 is energized and current flows from pin 86 to the high beam filaments and from there to ground. So in this case the fog lamp relay closes and the fog lamps come ON.

When the high beams are switched ON, then pin 85 is energized, which kills the current in the relay coil, the relay opens, and the fog lamps go OFF.

Obviously when the fog lamp switch is OFF, the relay will be open regardless of the state of the high beams.

I don't think this setup will turn OFF the high beams when the fog lamps are ON, but it will turn the fog lamps OFF when the high beams are ON.

A bit more on filaments is provided below

Scott

When the H4 lamps are on, then they are each dissipating about 60 watts, which at 12 volts is about 5 amps. This means the resistance of each filament, when ON, is 2.4 Ohms. Since there are two filaments, the resistance to ground at Pin 85 is only 1.2 ohms. Add to that the fact that incandescent filaments have much lower resistance when cold (per below, about 0.24 ohms each), and pin 85 is effectively grounded, as long as the current is low.

 

[rsporsche]

You probably want to avoid powering the fog lamps directly from the fog lamp switch since they draw a fair amount of current. So using a relay for that is a better option.

If you wanted to use a fog light cutout relay, you could wire it like this.
View attachment 211760
Here the fog lamp switch energizes the fog lamp relay (via pin 86). This closes the contact between pin 30 and pin 87.
Pin 30 is connected to pin 30 of the cutout relay.
Pin 87 a of the cutout relay is normally connected ted to pin 30 of that relay, so current flows into pin 30 and out of pin 87a to the fog lamps.

Connector 15 goes to pin 86 of the cutout relay.
If the high beams are on, then Connector 15 is energized (per your diagram), so the cutout relay switches form connecting pin 30 to pin 87a to connecting pin 30 to pin 87.

Since 87a is no longer connected to pin 30, there is no current to the fog lamps, and they go off.

You can also wire this using "negative logic" so the fog lamp switch would close to ground. In that case pin 85 of the fog lamp relay would connect to the Fog lamp switch, and pin 86 would connect to the fog lamp fuse. Closing the fog lamp switch woudl then ground pin 85 causing the relay to close, and the above sequence woudl then apply. Like this:

View attachment 211761

This approach is actually more convenient since you can still fuse the fog lamp circuit, but you do not need to run a wire from the fuse box to the switch. Instead you just write one side of the switch to a convenient ground.

HTH
Scott

absolutely zero desire to power the fog lights thru the switch. i have already solved that problem with the low beams. i am not going to worry about cutting the fog lights off if the high beams are on - i tend to agree with @HB Chris ... sometimes you want all the light you can get.

(in regard to your post about my post)
this is the problem i have with understanding the 74 wiring diagram - i don't find a ground ... that is why i asked the question. here is a larger screenshot of the 74 wiring diagram and the applicable legend. there is no brown wire touching anything except after it goes through the lights - both hi beam and fog lights. i do see a brown wire from 65 - fog light switch to 41 - wiper control unit. no ground wire to turn signal / dip switch, no ground wire to light switch. so perhaps you are correct, it is probable that the fog lights won't turn off if the high beams are turned on ... maybe that came in the late 70s as the first time i remember seeing that with the e21 320i

4 + 7 - high beam lights
15 - high beam / fog relay
16 - horn relay
18 - low beam relay
60 - turn signal / dip switch
62 - ignition switch
63 - headlight switch
65 - fog light switch
96 + 97 - fog lights

 

[ScottAndrews]

Possibly, i haven't dealt with any 5 prong relays. one quick question in your diagram - shouldn't red power generally come into #30? perhaps relays work backwards, i dunno.

i was going to run a single large wire from the battery into the interior to a fused block - and distribute to each side and each motor relay - running 4 big wires will be harder to get thru the firewall

Yes, a mechanical relay is basically a switch. It doesn't care which direction the current flows through the contacts.

Any your idea about using a single wire to a fuse and 4 wires out to the window motor relays is a good idea. The single wire doesn't need to be massive unless you expect to run all 4 windows at the same time...

 

[ScottAndrews]

…there is no brown wire touching anything except after it goes through the lights - both hi beam and fog lights.

See my later post on this. I think the relay gets grounded through the lamp filaments. So you answered your own question!!

If you have a 74+ car an do not want the fogs to go off when the high beams are on just disconnect pin 85, keeping all those wires in contact, and ground pin 85

 

[rsporsche]

Any your idea about using a single wire to a fuse and 4 wires out to the window motor relays is a good idea. The single wire doesn't need to be massive unless you expect to run all 4 windows at the same time...

i figure that you might press 2 windows at once, but not 4. if i remember correctly, you were also going to put an amp / subwoofer on the electrical feed ... that takes a bigger wire. i was probably going to run 10 or 12 gauge wire in, have a nice fuse block and then distribute to each of the 30 pin in the relays. haven't looked at any specifics of the motors, but 12 ga is 20 amps and 10 ga is 30 amps. if you are running a big ass amp, you might want 4 gauge ... but that's as big as the wire going to the starter

 

[e9Leveque]

I ran two separate 12 guage wires to the rear seat section of the car, since the amp/sub are under the driver's side rear seat. One 12-gauge wire is powering the amp/sub, the other is powering the two motors for the windows. The amp is not anything massive (nor is the sub) so I think I should be fine with that setup. My concern was more for how to keep the front end of the engine near the battery a bit cleaner. By the time that I have multiple leads coming off the positive terminal of the battery it seemed that perhaps running a lead from the positive terminal to a separate smaller fusebox would be a bit nicer. They even have fuseboxes that will hold some relays so may do that to hold the low beam ones.

 

[ScottAndrews]

...if i remember correctly, you were also going to put an amp / subwoofer on the electrical feed ... that takes a bigger wire.

Wasn't me!

 

[ScottAndrews]

Talking window relays, since the up/down nature of these requires two relays, which pencils out to EIGHT relays for all 4 windows, I am wondering if it might make sense to work out some other setup. Thinking about this a bit and doing a bit of parts research, I am thinking the entire window control could be vastly simplified by changing the relays for power MOSFETs. Below is a circuit that would eliminate a lot of wiring, and replace the large relays with chips that measure about 6 mm on a side and 2.5 mm thick.

Note that instead of routing power to the window switches, this simply grounds the common pole of the switch. The two switched poles then go to the gates of two power MOSFET devices. These devices can withstand 30 amps of current, and have an ON resistance of milliOhms. This could be implemented on a small board with connectors to mate up with the existing window wires that run from the console to the window, and could be attached to the window motor itself. I would probably encase the circuit in some sort of potting to keep it away from the elements. So, the wiring impact is really only to eliminate the B+ wires at the switches, and route B+ wires to the windows.