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Fusible link replacement alternative

57K views 37 replies 18 participants last post by  horsemn 
#1 ·
During the restore on my 93 D250, I installed a remote PDM (PNDB module) from a Freightliner M2 truck along with a 31 series screw top battery, and new cables in order to be done with the fusible link mess that is so problematic on these trucks.

It turned out to be a very nice upgrade to get rid of those fusible links, and be done with their corrosion and problems for good. Ive had a 31 series battery in the truck for years, with post top adapters. It was a complete mess with all the wires attached to the battery, and the rats nest I had with the fusible links.

Here is what I started with the fusibles on the main engine harness. Years ago, a fusible link blew on me in the dead of winter and started a small fire on the fender harness; and we repaired it "till spring" when it could be fixed properly...I found the rubber junction (broom) all corroded up and now slightly charred due to the small fire from the fusible burning. We removed it in -10 degrees, and this rats nest was born...I have to say, it did work fine for about 13 years...LOL:



Here is the solution, Main PNDB, Freightliner part number A06-72138-012; which is available for around $80; an alternative, if you want a simple battery disconnect switch, A06-72138-013--(you can wire up a low voltage rocker switch in the cab and disconnect the battery remotely, pretty convenient, about $150 for that one).



It includes 3 MIDI fuse connections, and 4 standard ATC blade fuse holders. I do not recommend using the MIDI's that come with it, they are way too heavy for what these trucks run.

Before wiring it up I went thru the entire harness, repaired any damaged wires, and replaced all the dry rotted tape with new vinyl and friction tape, as needed. I also went thru each circuit with a fusible link and identified what it feeds to be able to correctly size the fuses. Here is what the wires feed; in summary, with the fuse sizes I used after identifying the circuits. This is for 1991.6-93 trucks, 90-91.5 are slightly different. Check a wiring schematic for exact components.

40A MIDI; 12ga Pink/Black = Ignition Main Feed
40A MIDI; 12ga Red = Ignition Main Feed
40A MIDI; 12ga Red/White = Exterior Lamps/Headlamp Switch
30A ATC; 12ga Black/Red = Accessories/Power Mirrors
15A ATC; 16ga Pink = Hazard Flasher
100A Remote MIDI; 6ga Black = Alternator Main
30A ATC; 14ga Brown = ASD/Fuel Shutoff Solenoid Relay
40A MIDI; 12ga Red = Starter Relay (paired with 12ga Red/White, no fusible from factory)
20A ATC; 16ga Orange = ECM/A/C Relay

After finding all the wires and separating them, I made a new harness connection in the main engine harness. All connections soldered and covered with heat shrink tubing. Leave plenty of extra wire for locating the PDM:




I also added an extension onto the 6ga alternator feed to allow me to connect a remote MIDI fuse to it.

Here is everything cleaned, taped, and loomed together, and the new location for the PNDB mocked up. I used metal crimp ring terminals at the PNDB connections, soldered with heat shrink. The 4 pin connector in the PNDB is Freightliner part numbers 23-13153-410, FCI/10762803, FCI/10757690 (X2), and FCI/10762802, (this left me with an extra in case I damaged a terminal)...make sure to get yourself a good set of terminal connector crimpers for this, regular butt connector crimping tools will not work. The connector is very easy to put together once you crimp the terminals in, just snap them into the housing. I also put a bit of solder on the terminals for an extra secure connection.


Now to mount the PNDB, I used these rubber studded isolators from a Freightliner, part number 03-35804-000.


Pick a good dry location, and mount the PNDB with the two isolators. I picked the fender well rather than the inside of the fender, in case rain/water got in between the hood and fender. Once the splash shield is installed it will be high and dry. I also recommend spraying the terminals with a battery terminal protective coating. Freightliner makes a paint for this, and I will be coating mine with it here soon.


Here is the 2/0 main feed cable to the battery. I made this using a standard 2/0 x 5/16 terminal end, and a 90 degree battery terminal connector (Freightliner number 23-12776-123). I also connected the grid heater relays and alternator fuse to this terminal. I used a positive and negative cable from a Freightliner, part number JEI/28SP9873R110 (red) and JEI/28SP9851B062 (black), and cut them to the length needed, and crimed on new terminals for the starter, and engine ground. I also made a 2/0 engine to frame ground, and a 6ga battery to body ground off of the extra wire from the alternator circuit.




The new fuses in the PNDB:


Here is everything installed;



Hopefully this gives you a few ideas and helps you get rid of your fusible link problems. If you have any questions about my install feel free to ask.
 
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#2 ·
Very nice!!! I have been dreading the day I have fusible link issues and now this is a great way to fix it for good. What are the specs on the battery you installed?:yourock:
 
#8 ·
couple of questions, first, did you get the block straight from Freightliner? haven't found a decent source online for one.

also, you list 4 midi fuses in addition to the remote midi fuse for the alternator but the block only has 3. where does the 4th go?

40A MIDI; 12ga Pink/Black = Ignition Main Feed
40A MIDI; 12ga Red = Ignition Main Feed
40A MIDI; 12ga Red/White = Exterior Lamps/Headlamp Switch
30A ATC; 12ga Black/Red = Accessories/Power Mirrors
15A ATC; 16ga Pink = Hazard Flasher
100A Remote MIDI; 6ga Black = Alternator Main
30A ATC; 14ga Brown = ASD/Fuel Shutoff Solenoid Relay
40A MIDI; 12ga Red = Starter Relay (paired with 12ga Red/White, no fusible from factory)
20A ATC; 16ga Orange = ECM/A/C Relay
 
#9 ·
Yes, all came straight from a Freightliner dealer. It is proprietary stuff, so I highly doubt its available online.

The 4th midi in my list is paired on the same post with the headlamps/exterior lamps circuit (red/white). It is for the starter relay, and had no fusible link from the factory.
 
#11 ·
very clean install. Awesome!
 
#13 ·
You are welcome. Hopefully this will be a good long term solution for the electrical issues common on these trucks. Feel free to ask any questions, I will help any way I can.

I am going to add the part number for the glow plug relays; several have asked me where to get them:

They are available online from many sites, under part number 120-105711, just google search it; they are made by Westinghouse, White-Rodgers, and several other manufacturers. Make sure you use that part number, as it has an isolated ground circuit in it.

On a side note, I accidentally tested the PNDB the other day, I was checking the vacuum sensor to see if it worked, accidentally grounded the sensor power wire, and boom, blew the 40 amp midi instantly...engine shut off, dash went dead, good to know it all works. :laugh:
 
#16 ·
You will see the orange and red wire coming directly out of each relay; you can follow them from there.

The red ignition feed wire will be in the original "broom" junction on the fender.

If you still cant find them send me some pics of your wiring setup and I will check it out.
 
#17 ·
Alright thank you I will take a look at it tomorrow evening and let you know what I come up with. Also I was wondering on the side closest to the battery I have two small red wires that were wired into one white fusible link and also a bigger red wire and black wire. The black is for the alternator and the red to the battery but what are the two small wires for?
 
#21 ·
I think I got it figured out tonight. Someone has been into the wiring on my truck before so some of the wire colors did not match what you had mentioned but I was able to trace them back and I believe I have everything where it should be. I fired the truck up and everything worked as it should and so far nothing has caught fire so I'm thinking I will be good. Thank you very much for your help and for this awesome write up. It's kind of expensive but will definitely be worth it in the long run
 
#22 ·
Not a problem, glad you figured it out.

You are right, there are cheaper ways to do it; done right, this will be the last time you'll ever have to deal with fusible link or power wiring problems. Do it once, do it right IMO.
 
#24 ·
Pics fixed, thanks for posting here, I have been chasing threads fixing pics for a week since PB decided to charge an excessive amount of money to host pics. I have since changed photo hosting sites. :smile2:
 
#25 ·
Do you know if on the Freightliner disconnect # A06-72138-013 you listed,
does it need a maintained or momentary closure to operate it?

Looking at the Freightliner schematics and operators manuals, that electrical system is a nightmare especially the way it sheds loads during a circuit failure.

Your truck look clean under the hood, has it been repainted?
 
#26 ·
#27 ·
I’m kinda late to the party but I have a 90 model and I’m getting ready to do this on I was just wondering if the wire colors would all be the same throughout 89-93
 
#28 ·
The colors should be the same, mainly you need to go by the wire size.
 
#29 ·
Yes I will use the same size wire I just ment where they come out of the main harness the wires be the same colors for the same circuits so I know I’ve gotten them right
 
#33 ·
To all,

The freightliner MIDI/ATC fusbox used in this article is a Blue Sea Systems SafetyHub 100 Fuse Block #7725. I am not going to bother with this one I will be installing a SafetyHub 150 Fuse Block #7748. This allows one more MIDI and two more ATC fuses. I will start a new thread to review the electrical challenges I have had with this 1st gen cummins. I love the truck, but age will bring about changes.

electro_master
 
#34 ·
The worst problems I have had is fixing what other people have butchered, the people who don't have a clue should not mess with it, I'm sure you probably have some of that to deal with. I will follow your thread for more information you can always learn from others

Sent from my SM-N910P using Tapatalk
 
#38 ·
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