Help with simple relay operation

My car is an 89 US 328 with ABS. I've owned the car for about 1.5 years and the ABS system has never worked. Over the last several days I've been troubleshooting an unrelated issue, and in the process have gutted the car of all (or most) of the aftermarket wiring for an alarm system and the radio. In so doing, I discovered some incorrect wiring at the ignition switch. The wiring diagram for ABS shows a brown wire connected to the R terminal on the switch, and this wire goes straight to an "ABS System Control Relay". Unfortunately, I found the brown wire connected to P instead of R, and R had a cut wire that went to the radio that I removed. P has constant 12V, which is what WAS going to the ABS relay, and I've since learned from reading past threads here that P is not used. Anyway, I've now removed the superfluous red wire from R, and moved the brown wire from P to R so my switch now matches the diagram. Here's the switch and relay in the wiring diagram:

Image Unavailable, Please Login
Image Unavailable, Please Login

The relay #75e is mounted behind the passenger footwell. As you can see, the brown wire from R on the ignition switch provides switched power to the relay trigger input. Today I had this relay out of the car and I decided to bench test it. It appears to be a standard 4-pin relay that I assumed was "normally open", so I would expect that a trigger voltage would cause 30 to connect to 87, thereby supplying voltage to the "device" which of course is my ABS system. Here's what the relay looks like electrically:

Image Unavailable, Please Login

The wire colors that I added are true to the wiring diagram. The pinouts are exactly the same as represented above.

I tested the relay function by applying a constant 12V to pin 30, and then simulated the trigger by applying 12V to pin 85 as well. Pin 86 was connected to ground. Every time I connect or disconnect the trigger wire, I hear the relay click as expected. However, I was also expecting to see 12V output from pin 87 (power to the ABS system) when trigger voltage was applied to 85. Instead, the relay is acting the opposite way...that is, I'm getting 12V on 87 without any trigger voltage, and when the trigger voltage is applied to 85, the output voltage on 87 goes to 0V.

Is there something wrong with my test method? The reason I'm asking is, I don't know if a relay would ever fail with this type of behavior and it seems strange. I have no idea if the relay is original to the car, or if it is working as designed. Thoughts?

 

Steve, you and I downloaded the same pdf. A few days ago I asked the community if anyone had the right side of figure 9, and JFR delivered. Here's the thread with a pdf of the right half attached.

https://www.ferrarichat.com/forum/threads/help-need-328-wiring-diagram-9-abs.664973/

 

Mike and Steve, it is the right relay. Ferrparts has a picture of it in their catalog - https://ferrparts.com/parts/Ferrari/62567200

Image Unavailable, Please Login

My relay looks exactly the same, but there aren't any markings other than what are shown in the picture. 87a would only be used in a 5-pin relay. In this case it is not used.

So far, the only change to the circuit that I've made is to move the brown trigger wire from P (constant 12V) to R (switched power) on the back of the ignition switch. I'll put the interior back together and take the car out for a drive this evening and see if there's any change in behavior of the ABS light and system function.

The wiring diagram shows that the output from 87 either provides or cuts power to pin 30 of another relay, called "Control Relay for ABS System During Cranking" , which is 182 on the diagram. This is one of the relays in the front compartment next to the brake fluid reservoir. Relay 182 apparently uses 87a instead of 87. This evening I'll pull that relay and check for voltage at the 30 socket on relay 182 with key off and key on to confirm what relay 75e is doing downstream.

Image Unavailable, Please Login

I agree Mike, the backward behavior is puzzling in this particular circuit. I do know that there are "normally open" and "normally closed" relays. This one is behaving like it's normally closed. But of course it may be malfunctioning.

 

Yes, the terminal numbers are on the bottom. 85, 86, 87 and 30. No 87a.

I'm tempted to buy the replacement relay to see if it works differently.

 

Well, the ABS problem is going to the back burner. I tried to go for a short drive tonight and found the car won't start. I have a hunch my removal of the alarm components has disabled the starter circuit. More info here (post #12) - https://www.ferrarichat.com/forum/threads/question-about-whats-behind-the-passenger-floor-panel.664842/

 

Back to ABS. Went for a short drive a few minutes ago to observe the behavior of the ABS light after I made the wiring change from the ignition switch. Now, when I insert the key and turn it to any position, the ABS light does a single blink and goes out. It doesn't stay on for 4 secs like the other warning lights do.

During the drive, I did a panic stop to see if ABS is functional, and it isn't. The car skidded with no brake modulation from ABS. Curiously, the ABS light never came on, but the brake failure light did, and stayed on for the duration of the drive, even though braking action was unimpaired.

Back in the garage, I turn the car off and removed the key. The brake failure light went out, but the ABS light came on. And stayed on, until 5 minutes later when I pulled the battery disconnect. Reconnected the battery and the ABS light didn't come back on.

Next, I opened the front bonnet to see the ABS relays and fuses, and found a 30 amp fuse in the diagnostic holder! Well, that's one reason why the system wouldn't work. Maybe somebody put the fuse there to intentionally disable the system, or maybe they did a diagnostic and forgot to remove it. It appears to have been there for a very long time. It was just as dirty and grimy as the other fuses that were next to it. Maybe the alarm installer stuck it in there all those years ago.

So I pulled it. Wish I had done that before I did the drive, but I'll be able to taker her out again this afternoon.

The relay operation still makes no sense. I've had no luck at all trying to find out any info about it.

 

Pulling the diagnostic fuse didn't didn't seem to do anything different.

However, my relay appears to be toast now. The contact inside the relay no longer opens or closes in response to input voltage. I may have fried it in my earlier testing. So I ordered one, but no one has one in stock and they've been looking all over Italy for 3 weeks now. I'm not hopeful I'm going to find one.

So I opened up the relay and found that it has a small PCB inside, with a transistor and 5 resistors on it.

Image Unavailable, Please Login

Image Unavailable, Please Login

Image Unavailable, Please Login


Today I went for another drive, with the diagnostic fuse back in the car as it had been for years. Also with the busted ABS relay in the socket.

No more ABS light at startup or during the drive, but the brake failure warning light came on after 4 or 5 brake applications. After about a dozen more applications of the brake, the pedal all of a sudden became wooden and braking required serious foot pressure. My thinking was, with the ABS pump disabled by the diagnostic fuse, the accumulator gradually lost pressure during braking, which caused the warning light to illuminate early on, and the braking to become difficult later on. However, as I said before the fuse had been in the diagnostic position the entire time I've had the car and I've never had these issues before. I'm stumped.

Question - would there be any risk in trying a generic 4-pin fuse in place of the broken one? I don't want to fry anything else, but a regular fuse would only cost me $5 so I was thinking it might be worth a shot. Failing that, I don't know what else to do but take the car to Dave Helms and pay him an arm and a leg to see if his techs can figure it all out.

 

Oh, one more thing. When I got the car back in the garage, when I turned the key off, the ABS light came on for about 5 seconds then went out. At the same time, there was a steady buzzing noise from the front compartment that lasted about 30 seconds. Could that have been the ABS pump? This is so confusing.

 

Testing the transistor is a good idea, but how would the internet know whether it's a PNP or NPN? I don't have a schematic or specification for it. If I can figure out what I need, replacing it with a new one is probably 50 cents.

I will re-flow the solder joints. I don't see any evidence of cracks, but joints can go "cold" without any physical evidence. It can't hurt to do it.

 

Thanks! Using that info I was able to determine what transistor to get. It's a PNP. I bought several since they were only 38 cents apiece. However, I did pull the existing one from the board and it tested good though the forward voltages on the E and C were higher than they should be. The major problem with the relay is that the coil has failed. I'm thinking of using the coil from a second relay and combining the two relays with some jumpers.

The primary thing I need to know is how this relay is supposed to work. When the coil was working, it acted like the contact was normally closed and only opened up (cut output power on 87) when the trigger voltage was applied. I suspect that is not the correct operation, but until I come across someone who knows, I can't be sure.

 

In case anyone's interested, here's a clearer picture of the relay 75e which provides power to the braking system (not just ABS). Note the PNP transistor connected between the incoming voltage and the coil. I still have no idea what it's there for.

Image Unavailable, Please Login

 

Thanks Mike! I've done a lot of Googling on the subject but I hadn't come across a clear explanation like that link provided.

Ok, so it's probably protecting the ignition switch from a voltage spike which is the only thing upstream from the relay. I'm pretty sure there are cheap relays available that contain diodes, so if they're for voltage spike protection then one of them might be an acceptable solution. It's also common to find relays with resistors across the coil.

I'm of the belief now that there's no magic in this relay. I'm getting up the courage to just buy a relay with diode(s) and stick it in there and see what happens.

 

Hey guys, I went to eevblog and started a thread there to ask about the relay, and the brain trust are all over it! The engineers have produced a schematic of the relay just from pictures I've provided. It's in one of the thread posts.

Not only that, some of those guys are familiar with the Teves Mk 2, which surprised me.

Here's the thread - https://www.eevblog.com/forum/projects/automotive-relay-help/

 

I finally got a new relay in, and it's working like it's supposed to - the pump runs only when the key is on, and whenever the pressure switch calls for it. The new relay is available from Digikey and only costs a couple bucks - https://www.digikey.com/en/products/detail/cit-relay-and-switch/A21ASQ12VDC1-6D/12503356

No need for the unobtanium Ferrari original. However, it contains a diode across the coil to protect the ignition switch from voltage spikes, and the pin polarity is reversed from the wiring in the car. As a consequence, installing it requires jumpers between the relay and the socket. 85 and 86 are reversed. I'll rig up a more permanent arrangement when I get a chance.

Image Unavailable, Please Login

 

Mike, the new relay is internally wired according to the most common scheme, where 85 is ground and 86 is switched +12V. But the pinout in the 328's sockets is backward, where 86 is connected to ground and 85 is +12V. The original Italamec relay is wired that way too, so it matched. Why the relay and socket are wired that way is anyone's guess. I tried to find a new relay that would have the same pinout, while also having voltage spike protection, so I could just plug it right in, but no luck.

Having said all this, I found in my researching that most relays that provide spike protection use a resistor instead of a diode. Since resistors, unlike diodes, aren't polarity-sensitive, I could have just used one of those and plugged it right in. But since the original had 3 diodes and a transistor in it, I decided to go with a new relay that used a diode instead of a resistor. A diode apparently provides better protection for the upstream switch. I don't want anything to happen to my ignition switch which would be big bucks to replace, so I went with a diode relay. Using jumpers to swap 85 and 86 on the pins isn't the most elegant solution, but it works. I can think of two other slicker solutions that I'm going to investigate today, both of which involve changing the pinout in the relay socket. One is to see if I can open up that big relay box and get access to the wiring inside. If so, maybe I can swap the wires to the 85/86 pin sockets. Failing that, I might be able to swap the wires feeding the connector going into the box.

I may be making this much harder than it needs to be. Maybe the thing to do is just get a resistor-protected relay and use that instead of the diode relay.