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Relay question
HI
I have a question on what the forth relay is for in the junction box in the engine compartment. View the photo of the relays and the diagram that is posted on my rear door.
As shown, my diagram only shows three relays in to top row. Anyone have a clue what the fourth relay is used for?
Where do you go to order new relays? The part number on the relays that I have installed are magnecraft 88CPX-167 and OMRON MK2P-1. Since I’m having problems finding the Magnecraft relay, I suspect that the OMRON is a replacement for that relay.
I have looked through my prevost parts manual and I don’t see any diagrams that come close to what I see above. It seems that all the relays are using the same relay.
The problem I’m seeing right now is that my backup lights come on with I’m not in reverse. At the place I bought the coach, they troubleshot the issue was through relay R29. Eventually the backup lights turned off.
So three questions:
1. What is the forth relay on the top row for so I can know when it is causing issues and where?
2. Do the backup lights go through relay R29?
3. Does the OMRON relay replace the Magnecraft?
I’m pretty good about reading wiring diagrams, but I haven’t found any real good ones yet for this coach. On my 1976 GMC 4905, I had really good diagrams. I could troubleshoot just about any electrical problem from those. I’m still working on getting my head around all the components on this bus. I kept my 4905 pretty simple so it was easy to troubleshoot. It is great that they labeled all the wires really well, I just can’t find a diagram that tells me where that wire goes. Case in point, some of my light on my panel don’t work. I can find the wire number that seems to be the problem. I just can’t find where it goes once it disappears into the wire bundle. The wiring diagrams I do have, don’t have that number listed anywhere. So if you have a better way to troubleshoot these issues besides diving into all the spaces to crawl into, please let me know.
Thanks
Rod
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11 Replies
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Do your wires have ##s tatooed on them? that would answer your questions. Go to prevostcar.com under tech pub wiring diagrams. use last letter in your serial number and last 4 numbers example mine is w-6553 w= year and 6553 is unit number wire #’s are pretty well universal year to year. red is 24V yellow = 12 V fwiw Bob
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Thanks.. didn’t know about the color clue. that will help me a lot in following the wires.
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relay on bottom row looks like converter for taillight hook up for toad. converter modification. good luck all i can tell from pictures
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Rod,
You have a relay that was not part of the shell when it was built by Prevost. Someone or the converter added the relay, and you almost have to become a detective to figure out its purpose.
I think you can rule out those functions that Prevost lists on the wiring diagram associated with the relays they install. Even if the relay was an option Prevost would have listed it on the diagram which strongly suggests to me either the converter or previous owner installed it.
If I had to chase its purpose the first thing I would do is follow the wires back to the power studs and determine if it is a 12 or 24 volt power or if it is a key “on” or key “off” device. That information will help rule in or rule out some potential uses.
To suggest what it might be could be completely misleading, wrong, or even confusing so you likely have to start cutting wire ties and following wires. I share your pain because I had a similar situation in my first coach in which a heater for the Racor fuel filter was powered through the house batteries. I could not figure out why the house batteries were going dead after a week or so, and as it turned out a previous owner who thought of himself as a mechanic wired it through a relay so it was always on. It took a lot of tracing because I not only did not know where to start, I had no clue something like a fuel / water separator even had a need for low voltage electric power. I hope you tracing of wires is easier.
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Without reviewing the schematic I would suggest R29 is for the backup warning buzzer. If true, the backup lights would not be activated by R29.
As for which relay to use, I would only trust what is stated on the schematic. Relays generally come in 3 configurations. One is simply a relay. The second and third provide protection to the triggering system. One uses a resistor and another a diode. For all relays controlled bya DDEC 3 or 4, I would only use those with protection diodes.
FWIW, Prevost up through at least 98 used several 24V relays to control 12V loads. I assume this was due to the change to 12V loads, like exterior lights, when control systems were still 24V.
I can also believe converters may have put rear flood light controls in that used the back-up lights rather than installing additional rear flood lamps.
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[quote]Go to prevostcar.com under tech pub wiring
diagrams. use last letter in your serial number and last 4 numbers
example mine is w-6553 w= year and 6553 is unit number wire #’s are
pretty well universal year to year.[/quote]I have tried this and cannot find any combination that will return a result. Many of the responses say I need to enter a valid 3 or 3 digit number even though I enter J-1415. If not that, it says I don’t have a correct combo. Does anyone know what I might be doing wrong. It’s an 88 Country Coach 40′ XL Chassis has a late 87 build date.
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Under vehicle type pick
coaches 102
unit number
J-514
hit search
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So weird! Tried that many times and just tried it again. Still no good. Entered the number without the – in the middle j1415 and it worked.
Yikes!
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I have found it to be me most of the time! Sometimes I hit it just correct then next time nothing I do works?? Some time on converter shells the MTH selection gets you thru. Prob my clumbsy fingers or old brain. When I’m sucessful I print a hard copy. Now I need to learn to read?! Bob
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Did you ever find magnacraft 88cpx-167 replacement relays??
I need at least two of them.
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I did get three relays from Canada had to give my ss # for shiping to US
Now I can’t figure out how to start the engine, The check engine light does not come on at all just the gal telling me the fresh water level is low. How do you find all the circit breakers etc. for ingnition??? Is there any fusses at the key or behind it?
Bobby
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