I recently got this 91 940se and have been going through it. The diagnostic plug doesn't work so I went to the junk yard and found a better one. I went to wire it in and notices someone had cut the blue wire that goes to the led and wired it to a green\red stripe wire that goes to a smaller relay in the pic below. They also cut a blue\pink wire that seems to go to an empty spot in the smaller relay socket. Does anyone know what the smaller relay and socket go to and what the green\red wire goes to?

 

Have no clue what you are holding - oldest diagrams I have are from 1994 - b230ft was very similar to a 1991. There's not a single diagram showing everything going to (both) the obd boxes - here's from fuel and ignition. terminal 4 blue, 2 green/grey, 8 black, 6 yellow/red.

 

That is a mess indeed! First. Thing that black box doesnt even belong in the car at all!!!!
you are going to have try to find where the wires are unscathed on the wiring harness and cut and splice in original wires! From J yard!!
that box looks Saab ish????

Goodluck Goldenblock 2 million miles and running....

 

The original diagnostic port is laying in the left corner on the pick, the one from junk yard is still in the trunk. That mess was in the car when I got it. Wires going to the mystery box are.. a red wire coming from the coil of all places. And one coming from the battery and the wire that goes to the led in the diagnostic box is going there to. I'll untape and follow all the wire from the mystery relay and see exactly were they all go.

 

Ok you ll figure it out!! That relay is a standard relay for windows or locks i believe.

 

Thanks for the input. After work tomorrow I'll trace them all down and post where they go and see it would be safe to remove the rats nest.. I really like the car it runs great, just been trying to get it back in order and best off all it was free. My 94 mazda truck is getting tired and I really another daily driver.

 

coil pin 15 (blue wire) is a crude but easy place to get ignition switched power (on when the car is in RUN or START).

a standard bosch style automotive relay, pin 85 is + and 86 is - to the relay coil. pin 30 to pin 87 is the relay switch, normally 30 is power and 87 is the load you want to control with the relay.

 

So I traced down the wires going to the mystery relay. 30 goes direct to positive battery terminal. 86 goes to a chassis ground. 87 goes to terminal 15 on the coil.. 85 goes to the blue wire that powers the led in the on board diagnostic plug. If I remove the hella relay the car will not start. Plug it back in, it starts. If I put the blue wire back into the diagnostic port, it doesn't start. So a constant hot and ground and I'm assuming the blue wire is hot when key is on and a wire to the coil. Could they be supplying power to the coil from another direction? Cause it won't start if the hella relay is removed.

 

that sounds all kinda messed up. I'd have to dig up on my wiring diagrams for a 91 and see where the coil pin 15 and the diagnostic power wires come from normally. I wonder if this was some kludge to avoid replacing a fried ignition swithc or something??

 

That what I'm thinking. Looking at a diagram from a chilton book on the coil wires. Red\white wire goes to the power stage ignition. And the blue wire on term.15 goes to the interference relay. The red wire on 15 is what they added.

 

So blue wire that goes to the diagnostic port comes from the power amplifier and the ecu. The red and white wire from the coil on terminal 1 goes to the power amplifier. The blue wire on coil terminal 15 goes to the ignition. So I'm thinking they used the blue wire from diagnostic port to trigger the mystery relay to send power to the coil? Maybe the ignition switch is bad? If I unplug the blue wire on terminal 15 on the coil and test for voltage with key on and it's zero, would that mean bad ignition or at least no power from ignition to the coil?

 

Here's wiring and locations for ignition sys, wiring for fuel system. You should have a noise suppression relay, (#2/12) a small black rectangular relay mounted near the strut tower (it's not square, see attach picture, and the factory brand does not have the white writing on the side of it.). - that supplies power to the IGNITION coil on your model. Perhaps someone rigged in what ever that is you are holding. The noise suppression relay is number 2/12 on the diagrams, note how 2/12 supplies power to the coil after the fuel pump relay 2/13 turns on 2/12. So perhaps a section of the fuel pump relay failed and someone rigged in that square relay? Or the original round connectors for 2/12 failed (that is common, and hard to source) and it was replaced with that square relay that had spade connectors. So that became your ignition relay - powering the coil (and the throttle switch)

 

The voltage to the coil is around 9 volts. The relay they put in supplies the full 12 volts to the coil. But I can't find where the resistance is coming from.

 

here's the actual diagrams for a 1991 940SE.

Ignition:



and fuel injection:



there are some distinct albeit subtle differences. The power for the ignition coil comes from the RSR (2/12) which in turn gets it from the 'positive terminal', 15/1. The positive terminal in turn is connected directly to the battery via a heavy gauge wire. the RSR (radio suppression relay) is activated when the main fuel system relay comes on when the ignition is turned on.

 

Thank you Pierce this diagram is a little different than what I had and looks more like what I am seeing under the hood. Any idea why I'm only getting 9v at the coil? They seem to have put the extra relay in to get the 12v to the coil. The car runs fine with the extra relay plugged in. Unplugged I get 9v at the coil and no start. Plugged i get 12v at the coil and it starts. Not sure where to look to see where the resistance is coming from. It runs and I guess I should just leave it along but I just want to make her right.

 

Check the voltage at the rsr

 

Ok, I'll check it first thing after work tomorrow. The srs connector is in pretty poor shape. I got a better connector and relay from the junkyard. I planned on getting new female bullet connectors and rebuilding the connector anyway. I picked up 5\32 female bullet connectors today but of course they were to big. Do you happen to know what size they are? I thought I saw 4mm somewhere.

 

https://www.prancingmoose.com/blackv...l#4-polefemale also has a link to the bullet connectors.

 

Just went out and poked around the srs relay.with key on I get 12v at grey wire, 12v y\b coming from fuel pump relay and 12 at the red wire and ground at the black. I get 12 volts at the coil blue and red and white wires get 12v. With the extra relay unplugged still no start unless the extra relay is plugged in. I'm getting stumped here.

 

maybe that extra relay is also powering something else ?

but, you didn't see your 9V anywhere this time around? weirrdness.

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fyi, the red/white wire at the coil pin 1 is the timing signal from the ICU, its pulsed to ground to 'fire' the coil (actually the spark happens when the red/white wire STOPS being grounded). it will look like 12V when the timing signal is floating as you're just reading the pin 15 battery voltage through the coil since there's no current to speak of, then there's no voltage drop.