I've tried to armchair sleuth this out, but I'm finding the answer elusive. I have two relays sitting side-by-side on top of my battery. They are these:
12V, 30A, Valvar type 230006, marked with part number 1 364 986. This is referenced on E28 boards as a "relief relay" for an auto tranny, but I have a manual. What are these for on E12s, exactly? Bonus points for the current BMW part number.
Also helping from my armchair . Did your E12 come from the factory with a manual? When I google your part number, it comes up as an automatic trans. relay as well. You may have to get out of your armchair and trace the wires to find out if there is another purpose for this relay.
"Eleanor" for example, doesn't have this relay (you mentioned it was above the battery), meaning that she came from the factory as a manual. I know this because I'm the third owner, and I also have the 4-speed the P.O removed when he installed the 5-speed. If your E12 was a manual from the factory like mine, then there would be no reason for BMW to add useless relays, especially to keep the bean counters happy.
I found them in the Haynes US-spec 528 schematics labelled as "Stage I" and "Stage II" relays. They control the A/C compressor and the aux fan via the various temp switches.
Eric, I can share some of the knowledge I have of my '79 electrical system.
The stage I and stage II relays (in my car, they're tacked onto the outside of the fuse box like an afterthought) are triggered from the 90C and 99C temp sensors in the radiator, and spin the front aux fan at 50% via its resistor and 100% speed respectively. The stage I relay is also linked to the AC compressor, so the aux fan comes on at half speed with the AC.
The auto trans/inhibitor relay is the Park-Neutral starter motor cutout, but this is located under the dash and intercepts the start signal from the ignition switch. I eliminated mine, factory manual cars don't come with this relay obviously so yours won't have it.
The relief relay - took me a while to figure this one out. It is triggered by the starter signal, and it cuts power to non-essential items in the fuse box so that all power can be directed to the starter and the coil during cranking.
Other cars do this via the ignition switch, e.g. the 'on' position for ECU, coils, fuel pump stays powered while 'ignition' line for the radio, power windows etc. cuts out when the key is turned to the 'start' position. BMWs have a relief relay that instead 'relieves' the electrical system of this non-essential load via the black and yellow star signal line in the fuse box. A poor translation for whatever the German word is I assume.
It's a strange name for that system and on forums can get mixed up with the inhibitor relay.
OK, I have a strange problem that I've isolated to the Stage I relay connector block. The relay tests good. If I use a voltmeter probe I pick up 12 volts between terminal 30 and ground, but if I plug in a jumper (or the relay) the voltage won't turn the fan. The aux fan runs on 12 volts supplied to it directly from a power supply, and the ground tests good to the ground point behind the battery.
I can also turn the fan using a 12V power supply connected to the 87 terminal and the fan ground, so the wiring to the fan is good. Supplying voltage to terminal 87 of the Stage II relay also turns the fan. The ground in the relay connector is also good and the relay clicks when the A/C switches on.
What the hell? I'll measure the voltage at the fan connector tomorrow and see if it differs from the voltage measured at the relay block.
That is weird. When you measure the voltage on each side of the relay when it turns on, do you get 12v on both sides?
Wondering if there's some high resistance somewhere, so you're seeing 12v, but put it under load and the voltage drops down, lower than can drive the fan.
Might also be worth checking the fan resistor too, I've read here that they can burn the wiring contacts which would also result in high resistance.
Lock, terminal 30 is actually 11.4 Volts, which isn't right. The battery is 12.8 V. If I shunt the black wire from the Stage 1 relay connector to the battery (+) the fan comes to life with authority. There's something happening, I suspect you're right and will trace the red/green wire. It looks to head straight to the fuse box (fuse 17, 25A).
I checked the fuse box and that's when I saw the green fuse. Wait a minute ... green? The aux fan is wired to the 25A fuse at position 17 ... 25A fuses are blue. At least new ones are. Decades-old ones turn green. And get all kinds of crap caked on them. And get loose. And turn 12.8V at 25A into 11.4V at way-too-few-amps-to-turn-the-aux-fan.
Thanks Lock. There's also a lesson here for not breezing past an obvious sign of a problem and check all assumptions. I've trained myself to always check the grounds, but in this case had I carefully checked the fuse after seeing 11.4V at the relay, I'd have solved this earlier.
Great catch on the fuse. I'm still running the original fuses because they 'look' ok but should probably replace them. I have at least replaced the relays.
I thought it might be a long shot, but I have seen that before - voltage looks ok, but then drops to not enough under load due to resistance.
I was also going to say I've read here that the front aux fan bearings also get gummy over time and cause the fan to require more current to spin (not sure if there's a FAQ but I recall you can disassemble and re-grease), so couple that with low current and you'll get the no show you saw. I've meant to regrease mine but can't immediately see how to get it out easily.
Come to think of it, I've read that the blower motor fuseholder can melt the fusebox plastic. It might be this same issue - blower fan needs more current to spin, and high resistance at the fuse causes enough heat to melt the box. PSA to keep the fuse box links clean with fresh fuses.
. Did your E12 come from the factory with a manual? When I google your part number, it comes up as an automatic trans. relay as well. You may have to get out of your armchair and trace the wires to find out if there is another purpose for this relay.