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  #11  
Old 05-13-2018
Charlie Fox Charlie Fox is offline
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Default Super naive questions

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Is this the ZF ECU plug? And is the ECU the white box on the wall?
Plug #19 is where the voltage needs s/b 12v?
When I checked key on, unplugged it shows 10.5v.
I don't see any relays or anywhere that a wire has been cut or where the loom has been altered.

Now here's a picture a little wider angle.
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The big plug has no power that I can see, of the 2 white wires 1 has like 6/7 volts the other is dead.
What do I do about this stuff?

Now the questions start...I've added trans fluid to the lowest fill points and it shifts great, I think, the 2nd gear lockup thing is a little weird. To check the underside dipstick do I need to use jackstands?
Should I still add the relay to ensure 12v to the ECU? This...ZF LOW VOLTAGE FIX PDF.pdf?

So I cut the red #19 wire, attach plug side to relay, cap current supply side.
Do I need to wire ground to something specific or any solid ground?
Can the 12v fused input to relay come from the bus bars in the background of picture 1?
To wire into the ignition do I need to take the dash apart to get to the back of the switch or...?

Thank you
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Last edited by Charlie Fox; 05-13-2018 at 10:09 AM.
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  #12  
Old 05-13-2018
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your attachments do not work.
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  #13  
Old 05-13-2018
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The 12V can come from anywhere but it is best to run a dedicated 12V power source direct when the ignition switch is in the on position. Your problem is the current feed line is supporting other items that's the reason for the voltage drop to 10.5. A best ground would be at the chassis. The PMMI box behind the nose coweling right center of the driver's windshield has a set of miniature relays that was supporting the ZF and other items. Just ignore it and go with a direct power source. Bob Esswin, a ZF factory trained tech and knowledgeable on Blue Birds of Precision Transmission, in Colmar, PA did mine and all problems were solved. You can jack up the bus if you need to but use caution and make sure it is level to get a correct reading from the transmission side mounted transmission dip stick. Good luck.
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  #14  
Old 05-13-2018
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Quote:
Originally Posted by Charlie Fox View Post
Attachment 55375
Is this the ZF ECU plug? And is the ECU the white box on the wall?
Plug #19 is where the voltage needs s/b 12v?
When I checked key on, unplugged it shows 10.5v.
I don't see any relays or anywhere that a wire has been cut or where the loom has been altered.

Now here's a picture a little wider angle.
Attachment 55376
The big plug has no power that I can see, of the 2 white wires 1 has like 6/7 volts the other is dead.
What do I do about this stuff?

Now the questions start...I've added trans fluid to the lowest fill points and it shifts great, I think, the 2nd gear lockup thing is a little weird. To check the underside dipstick do I need to use jackstands?
Should I still add the relay to ensure 12v to the ECU? This...Attachment 55374?

So I cut the red #19 wire, attach plug side to relay, cap current supply side.
Do I need to wire ground to something specific or any solid ground?
Can the 12v fused input to relay come from the bus bars in the background of picture 1?
To wire into the ignition do I need to take the dash apart to get to the back of the switch or...?

Thank you
There are two bus bars behind the carpeted panel lower & forward,
One is battery hot all the time, use this for the power wire don't forget the fuse, the other bus bar is ignition hot use this for the relay trigger coil.
Follow the service note, the schematic, Bob G's earlier post and there is a write up by Mark Bragdon. it has been several years since I wired one of these relays, so I can not give step by step directions,, Just cut into the grey woven wiring sheath and find the correct pink wires.
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  #15  
Old 05-14-2018
Charlie Fox Charlie Fox is offline
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Default ZF relay mod

OK...so I should've started with electrical is still quite the mystery to me but I'm a scrambler.
I have 2 bus bars 1 is hot whether the key is on or not...
Bus bar 2 is hot when key is on...
Following the PDF...
I clip the red/pink wire, #19 on the big plug, on the ECU,
splice to the #87 pigtail on the relay...the cut wire going to the plug I tag and tape the end.

Ring end on fuse pigtail to "key on" bus, splice other pigtail to #85 relay pigtail.

Ring end on fuse pigtail to "constant on" bus, splice other pigtail to #30 relay pigtail.

#86 relay pigtail goes to ground. Where is the best? Do the buss bars have grounds?
Go to the engine block? Bolt on the steering wheel support? What is floating ground?

More questions...are the relays we are talking about the same relays that are for the headlight, taillight, fuel pump...?
And what size fuse?
Thank you

Next question is does anyone have any idea what this plug could be for?
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  #16  
Old 05-15-2018
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I'm thinking Charlie needs someone with automotive 12 volt experience to help.
Better yet someone with this ZF experience , that plug with the wires?, seems someone had made some changes, electrical troubleshooting is required.
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  #17  
Old 05-15-2018
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Turn the plug over so we can see the other side of it.


Just use the switched buss bar and attach a suitable gauge wire to that. Install a fuse inline and attach to the # 19 wire. That relay will add many unneeded connections and servers no purpose for this application. The run is very short, what less than three feet, and your not dealing with a lot of amps.
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Last edited by Rick; 05-15-2018 at 07:25 AM. Reason: added
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  #18  
Old 05-15-2018
globetrottin globetrottin is offline
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Mine is working fine after taking a couple tries to figure out the wiring. It really is simple once it's figured out. Here's my attempt at simplifying based on what I found and did. This is all with the ignition switch off, key out, but bus master power switch under the dash on.

First of all, the big 37 pin plug with lots of colored wires going into the top of the ZF ECU (electronic control unit? It's taller than a toaster but not as wide, and attached to the wall of the bus) behind the panel under the driver's window is the the right place to start. One of the pins in the plug has two red (some people say pink) wires going to the same pin with number 19 stamped on the wire every few inches on both wires. Makes sense that they are the same wire and number since both wires are going to the same pin in the big plug. Amazing to me how all of the wires on this bus are numbered.

Both of those red #19 wires coming from the big plug on the ECU are part of the big fistfull of wires wrapped together in a black sheath. The 37 pin plug has a release lever of sorts on the end with the wires. Release that and the plug comes off. On the front of the plug is a single screw. Loosen the screw and the plug can be separated into two pieces top and bottom. At that point you can push the wire bundle's sheath back to see the (2) red #19 wires going into pin 19.

The trick is to figure out which one of the two wires to cut. You can't tell by looking at them, so just pick one and cut it, but cut it at least 4 inches away from the big 37 pin plug so you have something to work with. If you are lucky and cut the right one, your multimeter will show voltage on the end disappearing into the wire sheath toward the bus and zero volts on the wire end going to the plug. If you got unlucky, you will see zero volts on the part going toward the bus in the wire bundle and see voltage on the cut end that goes to the plug. If that's the case, just splice it back together and go to the other red wire and cut it and you should see that the zero volts cut end is the one that goes to the plug.
The part of the cut wire that disappears in the wire sheath toward the bus showing some voltage can just be capped, covered, taped, or otherwise permanently insulated and forgotten about.

The part of the cut wire with zero volts going into the plug needs power from a strong source like one of the bus bars conveniently a foot or so ahead of where you're working, on the same wall of the bus, with lots of wires tapped into them. Go ahead and test those bus bars now with the key off. One will have pretty much full volts from your battery (13 or so with good full batteries?) and one will have zero. The one that has full power has to go to the cut end of the red wire that you left hanging out of the plug.

One of my bus buddies had told me not to put a plain wire directly from the bus bar to the #19 wire going into the plug. He said to use a fused relay to supply power. Rick's idea of just using a fused wire should work fine as well, but I did it the slightly more complicated way. So, I have a wire from the bus bar to a 9V fuse, then continuing to pin #30 on a standard relay, then a wire from pin #87 on the relay to the #19 wire. The part of the relay that decides whether it's making a connection or not gets wired to the other bus bar - the one that is currently reading zero. That wire goes to pin #86 to the bus bar. Then one more wire from pin #85 to ground, like a screw or bolt on the bus wall.

I've only driven 20 miles or so since I did mine, but it's like a new bus compared to before. I had gone through the gyrations of checking fluid levels in the ZF, changing the ZF fluid and filter, etc, etc. but this was the answer to smooth shifting. Also... smooth downshifting, as a bonus!
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Last edited by globetrottin; 05-15-2018 at 08:15 AM. Reason: corrections
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  #19  
Old 05-15-2018
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Quote:
Originally Posted by globetrottin View Post
Mine is working fine after taking a couple tries to figure out the wiring. It really is simple once it's figured out. Here's my attempt at simplifying based on what I found and did. This is all with the ignition switch off, key out, but bus master power switch under the dash on.

First of all, the big 37 pin plug with lots of colored wires going into the top of the ZF ECU (electronic control unit? It's taller than a toaster but not as wide, and attached to the wall of the bus) behind the panel under the driver's window is the the right place to start. One of the pins in the plug has two red (some people say pink) wires going to the same pin with number 19 stamped on the wire every few inches on both wires. Makes sense that they are the same wire and number since both wires are going to the same pin in the big plug. Amazing to me how all of the wires on this bus are numbered.

Both of those red #19 wires coming from the big plug on the ECU are part of the big fistfull of wires wrapped together in a black sheath. The 37 pin plug has a release lever of sorts on the end with the wires. Release that and the plug comes off. On the front of the plug is a single screw. Loosen the screw and the plug can be separated into two pieces top and bottom. At that point you can push the wire bundle's sheath back to see the (2) red #19 wires going into pin 19.

The trick is to figure out which one of the two wires to cut. You can't tell by looking at them, so if you have a gizmo for checking for current on the outside of a wire without cutting it, find the one that has current to it. If not, use the sharp needle probe on the red wire from your multimeter (set correctly to its 20V DC range, at least that's how mine works to measure things in the 12-14 volts DC range) and push the needle into one of the red wires and touch the black multimeter probe to ground, like bare metal on the steering column for example. If it reads zero, you have the wrong one. If it shows some DC volts in the line then it's the correct one. Cut the one with volts in it, but cut it at least 4 inches away from the big 37 pin plug so you have something to work with.
The part of the cut wire that disappears in the wire sheath can just be capped, covered, taped, or otherwise permanently insulated and forgotten about.

The part going into the plug needs power from a strong source like one of the bus bars conveniently a foot or so ahead of where you're working, on the same wall of the bus, with lots of wires tapped into them. Go ahead and test those bus bars now with the key off. One will have pretty much full volts from your battery (13 or so with good full batteries?) and one will have zero. The one that has full power has to go to the cut end of the red wire that you left hanging out of the plug.

Smarter people than me have said not to put a wire directly from the bus bar to the new wire. They say to use a relay. They also say to use a fuse. So, I have a wire from the bus bar to a 9V fuse, then continuing to pin #30 on a standard relay, then a wire from pin #87 on the relay to the #19 wire. The part of the relay that decides whether it's making a connection or not gets wired to the other bus bar - the one that is currently reading zero. That wire goes to pin #86 to the bus bar. Then one more wire from pin #85 to ground, like a screw or bolt on the bus wall.

I've only driven 20 miles or so since I did mine, but it's like a new bus compared to before. I had gone through the gyrations of checking fluid levels in the ZF, changing the ZF fluid and filter, etc, etc. but this was the answer to smooth shifting. Also... smooth downshifting, as a bonus!

What purpose do you think the relay serves? I would really like to know how it can have any effect. Just put the new power wire on the switched buss bar and the problem is solved. We ran our 90 SP tens of thousands of miles with this simple fix. And by the way, it was done by Precision Transmission. The runs are so short there is no need for a relay.
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  #20  
Old 05-15-2018
globetrottin globetrottin is offline
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Quote:
Originally Posted by Rick View Post
What purpose do you think the relay serves? I would really like to know how it can have any effect. Just put the new power wire on the switched buss bar and the problem is solved. We ran our 90 SP tens of thousands of miles with this simple fix. And by the way, it was done by Precision Transmission. The runs are so short there is no need for a relay.
Rick, I agree with you that a relay in not necessary to do this repair. It was a suggestion made to me as "it can't hurt" which is probably true as long as the relay works. I think the only good that came of it for me is that it made me learn a bit about how relays work. I have amended my long description post of the repair to explain that your fused wire suggestion is simpler and leaves less room for error. I kind of wish I had skipped the relay part because it would have saved a lot of head scratching time for me, but in the end it's working and I learned a little something.
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