Power Distribution Relay Issue

Discussion in 'Electrical' started by JunkyardDog, Apr 18, 2015.

  1. JunkyardDog

    JunkyardDog Member

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    I am in need of the schematic for the power distribution block for a 2003 Expedition. The relay labeled as R203, and called the PCM Relay, has now been replaced 3 times. Pin 5 of the relay is melting the plastic of the relay. It has been taking SIX to EIGHT MONTHS months to show any symptoms. I know because I have been checking it monthly.

    I now have an additional issue.

    I went to install a new relay and the new relay would not work. I started to do some troubleshooting and the receptacle would not hold a spade connector.

    I suspect that due to the heat involved, the receptacle of that pin of the relay is now being allowed to pull back from its correct position and no longer makes contact with the new replacement relay contact.

    How difficult is it to pull the block out to make the repair?

    Even if I cannot repair/replace the block immediately, I need to find the source of the current draw. What useful advice can you give on this issue?
     

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    Last edited: Apr 18, 2015
  2. stamp11127

    stamp11127 Super Moderator Staff Member

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    What is the amp rating of the relay you are trying to put in? You will have to remove the fuse box and disassemble since the female connectors are through hole soldered. Fuel pump relay is problematic on these - guess what is on that circuit? Check and see if there is room to add 12 or 14 ga wire to increase the amp capacity of those circuits while you have it apart.
     

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    Last edited: Apr 18, 2015
  3. JunkyardDog

    JunkyardDog Member

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    To be honest, I do not know the amp rating of this relay. In fact, I also do not know the rating of the original OEM relay either. I am technical and I do understand the importance. AutoZone provided the replacements (all 3 of them) and there is an assumption that since that is what their system showed as the replacement, and that it it looked physically the same in appearance, that it it must be the correct item. The fact that they worked for, in order of working time - 13 months, 9 months, 8 days, It seemed like they were not initially considered the wrong part.

    I was able to extract the distribution block without complications. (Though, the comments and gestures from my wife could have been toned down. I was starting to feel like she really did not appreciate me fixing her vehicle.)

    I found the issue to be the terminal that leads to pin 5 of the relay and the solder to be heat stressed. But, it was not open (as in an open circuit) and the copper was in rather great shape. The receptacle "pinchers" were spread a little more than normal and was just not a comforting fit like it should have been.

    I agree with your concerns over the amperage capabilities. However, I think the contact becoming resistive is the major source of the issue. In this case, I think the issue (resistive connections) escalated into runaway and cause more problems than the actual component's ability to carry current. Still, a fix is still needed.

    I really don't think that I will have an luck finding replacement connectors that can hold as well as the originals. And, my money tree is still producing slower than I need it to be, to replace the whole block. So, what I think I am going to do is I am going to hardwire a Bosch relay socket/cable and employ a Bosch relay. I'll be sure and secure everything so there will not be any issues from vibrations.
     
  4. stamp11127

    stamp11127 Super Moderator Staff Member

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    Once you have the pcb out take a close look at the female quick connects that are soldered on for the relays. They may have an identifying logo stamped in them.

    I was able to find the male quick connects but not the female for through hole.
     
  5. JunkyardDog

    JunkyardDog Member

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    Pulling the block proved to be much easier than I anticipated. One 10mm nut and one 11mm nut and the rest were snaps or snap in connectors. The block, as a whole, is also extremely light.

    I took pictures along the way to show the fuse size placement, etc. Then, I took all of the fuses and relays out. (Pictures are attached for most of the text descriptions.)

    The top and bottom just snap together. Be careful so you don't open a 'jack-in-the-box" and throw parts everywhere. It is not that everything is extremely loose. But, when the two halves are apart, pieces can fallout. Things are that loose when not all assembled.

    Once the top is off, you can see that there is only one connector board and layers of plastic fit together. The main power bus is layers of metal between the plastic layers. I did not take any of the plastic layers apart. My issues did not take me in that direction.

    All that holds the connector board to the plastic layers are some small clips. Take note that the clips can be put on in the wrong orientation.

    My issue is with one female connector. (I did not look close enough to see if they were marked with information - brand, etc.) While it looked stressed and oxidized, it scraped off easily and cleanly. The pinchers proved to be too loose and ripe for arcing. That will produce the oxidizing and operational issues.

    I soldered buss wire to the back side of the board to beef up the trace. I soldered some metal strips to the existing contacts to extend the connections through the holes that the relay normally pushed through. This created an array of male connectors poking through the case when it is assembled, for attaching female connectors. I attached a Potter & Brumfield relay and harness (Bosch Style) and mounted it with a single screw to the case (making sure the screw did not interfere with anything behind it).

    So far it is working great.

    I'll take a picture of the finished install ASAP. I had to get on to some other tasks! I also meant to take a picture of the back side of the board where I beefed up the trace that was stressed. Unless I have to take it apart again, and I hope I don't, I won't have this picture.

    Overall, it was much easier than I expected.
     

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    Last edited: Apr 20, 2015
  6. JunkyardDog

    JunkyardDog Member

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    I still have work to do!

    I need to find out nominal, minimum and maximum current draws for the downstream legs so I can determine if there was more to causing the issue in the first place.

    The attached picture shows the descriptions of the circuits that load this relay.

    Does anyone know these values for these sub-circuits?
     

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  7. stamp11127

    stamp11127 Super Moderator Staff Member

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    I would use 80% of the correct amperage fuse that is supposed to protect each branch circuit. But the main fuse needs to be able to cover the entire draw of all the branches together - 55 amps.
     
    Last edited: Apr 20, 2015
  8. 2003FordGuy

    2003FordGuy Member

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    JunkyardDog. I am having this same exact issue. But one question. Where did you get the metal tabs to solder into the circuitboard?
     
  9. stamp11127

    stamp11127 Super Moderator Staff Member

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    203fordguy you may not get a rely from him. The last time he was on the forum was 9-2016
     
  10. 2003FordGuy

    2003FordGuy Member

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    Man, just when I thought I had the answer to my problem. Lol. OK stamp11127. Thanks.
     

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