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Discussion Starter · #1 ·
Hi all,

Long story short - I fried my 034 EFI relay board (which was) providing switched power to ECU, Ignition Coils (x4), Fuel Pump, and Fan.

The ECU relay is the one that has melted, and I believe the damage goes beyond the socket. I did try to replace the relay itself, no luck.

I have determined that the relay boards are no longer available, so it is looking like I'll need to re-wire and determine a new solution.

Unfortunately, I am not sure how to use all my existing wiring most efficiently because I'm not sure how the relay and circuit board interacted.

Everything I need to re-connect is sitting there neatly wired to the relay board... can someone give me a hand figuring out the best solution to re-wire?
 

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1990 Coupe Quattro (3B, K26/K27, VEMS), 2007 S8
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Don't have a direct answer, but if you have a Digital MultiMeter as well as the specs for the relay, then you should be able to figure it out.

Looks like relay #2 is triggered by the same +12v signal as relay #1 (IGNSW), so the other trigger for the relay is probably BAT- (but might be ECU-)
Looks like a standard 5-pin Bosch style automotive relay socket.
The relay coil trigger pins for those are typically 85 and 86. (left and right on the socket in your picture, not necessarily respectively).
The common power pin is pin 30 and the one that looks melted on the socket. This would go to BAT+
The other two pins are probably both pin 87 (for a 5 pin relay with two Normally Open output pins). These would go to INJ-P and ECU+ respectively.

Once you have the wiring sorted, you could connect up a free-floating relay to replace relay #2, or try to simply bypass the circuit board for the common power pin.

Make sure you don't have an overcurrent problem elsewhere that led to the overheated pin.
 

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Discussion Starter · #4 ·
Don't have a direct answer, but if you have a Digital MultiMeter as well as the specs for the relay, then you should be able to figure it out.

Looks like relay #2 is triggered by the same +12v signal as relay #1 (IGNSW), so the other trigger for the relay is probably BAT- (but might be ECU-)
Looks like a standard 5-pin Bosch style automotive relay socket.
The relay coil trigger pins for those are typically 85 and 86. (left and right on the socket in your picture, not necessarily respectively).
The common power pin is pin 30 and the one that looks melted on the socket. This would go to BAT+
The other two pins are probably both pin 87 (for a 5 pin relay with two Normally Open output pins). These would go to INJ-P and ECU+ respectively.

Once you have the wiring sorted, you could connect up a free-floating relay to replace relay #2, or try to simply bypass the circuit board for the common power pin.

Make sure you don't have an overcurrent problem elsewhere that led to the overheated pin.
Unfortunately I am not well-versed in relays... I admit I need to study up on that.

I would like to bypass relay 2 if possible, wire it "free-floating" as you say, but I am not sure how to do that but also use the rest of the circuit board's connectivity. I did wire power directly to my ECU and confirmed I can connect to it, all seems OK, but I did not get any fuel pump- which seems to tell me that I wasn't "triggering" the 3rd (fuel pump) relay.

I do have a digital multimeter. If I gave you some type of readings, would that help you determine anything further?

Appreciate your input!!!
 

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1990 Coupe Quattro (3B, K26/K27, VEMS), 2007 S8
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Yeah, happy to help

Relays 101:
A relay is basically an electrically controlled switch. There is a small coil that generates a magnetic pull to close a switch. The coil can operate with a small amount of current (like what can be supplied by an ECU), and close a circuit for a system that otherwise pulls quite a bit of current (like an electric motor in a pump).
That's the basics of a simple "dumb" relay. There are other "smart" relays used in automotive systems where the relay takes many inputs, and a circuit board processes the signal to determine when to close the load circuit.
On your relay board, they all appear to be "dumb" relays. That makes life easy.

Relay #3 (fuel pump relay) is triggered by a grounded signal in the ECU for the fuel pump (GPO_0). This is a safety mechanism to shut off the fuel pump if the engine isn't running. So if your ECU isn't getting power, then I wouldn't expect it to activate relay #3.

I would still focus on the socket for relay #2 as the most likely to be problematic.
Let's label some of the socket pins based on your picture:
Top (burned out in picture) - 30
Left - 86
Right - 85
Center - 87-1
Bottom - 87-2

Now, take your multimeter, set to Ohm (resistance) mode and see where each of those pins connect to on the terminal stip. It should read very close to 0 ohms, certainly less than 1 ohm.

For each of the pins above, make a note of which pin it connects to and report back.
Make sure you put a fuse into the fuse holder for #2. For testing the rating of the fuse doesn't matter, looks like a 30A fuse is what is normally placed there.

Pin 30 should have connection to BAT+, but I would suspect that it either has no connection to that or the connection is very high resistance.
 
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