M210 Locker Blowing Fuses

[Alecnavarro]

Recently did a M190 to M210 front differential swap in my Big Bend, its a brand new unit from Ford Performance. Install went great, about 150 miles on it now but I have yet to get the locker to function. I had seen others wire them directly to their aux witches without issue and since mine wasn't equipped with them, I opted to wire it to my switch pros that currently runs all my lighting. The moment I press the button it blows a 15 amp fuse.

Things I have tried so far:
-Eliminating switch pros as culprit by using a fused jumper directly to battery.
-Unplugged the connection at the diff and hit the switch to check for short in external wiring (nothing happen /doesn't blow fuse)
-Read OHMs at locker connection in the housing, my reader showed 0.00 (same as functioning rear locker)
-Pulled O-ringed connector out of housing and looked for obvious broken wires inside (everything seemed fine from the little I could see)

Am I doing something wrong? Out of ideas beside opening it up and trying to diagnose the locker itself.

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[Brian_B]

Read OHMs at locker connection in the housing, mine reader showed 0.00 (same as functioning rear locker)

You should be reading 3-5 Ohms on the coil. If you are seeing a hard 0 ohms there is a problem.

Easiest place to check would be at your switch and check through all the wiring for the coil to ensure there isn’t a short in the wiring harness or anything.

I have had bad coils (0 ohms and blows fuses instantly) although it seems to be a bit rare.

 

[Alecnavarro]

You should be reading 3-5 Ohms on the coil. If you are seeing a hard 0 ohms there is a problem.

Easiest place to check would be at your switch and check through all the wiring for the coil to ensure there isn’t a short in the wiring harness or anything.

I have had bad coils (0 ohms and blows fuses instantly) although it seems to be a bit rare.

Hmm I’ll have to attempt that again. I got 0 ohms at the rear locker is well and I’m 100% sure it works.

 

[Alecnavarro]

The following two pictures are me testing the leads coming up directly from the locker. 0 ohms plugged in and open when unplugged. I’m not too savvy on the electrical side of things, maybe I have it on the wrong settings?

 

[Alecnavarro]

Here is a pic of testing ohms at the rear again. After this was taken, I triple checked that it locks and unlocks just fine.

 

[Bigmoose]

Here is a pic of testing ohms at the rear again. After this was taken, I triple checked that it locks and unlocks just fine.

Set the scale to 200, not 20k. See if you get different readings.

 

[Alecnavarro]

Set the scale to 200, not 20k. See if you get different readings.

Tried it, same result. Took of the housing union thingy and tested the locker plug directly. 0 ohms

 

[Brian_B]

This is a brand new coil I recently swapped.

 

[Alecnavarro]

This is a brand new coil I recently swapped.

Interesting, so if my reading of 0 is correct the coil is toast? Genuinely confused why I'm getting 0 at the rear then?

 

[Brian_B]

Interesting, so if my reading of 0 is correct the coil is toast? Genuinely confused why I'm getting 0 at the rear then?

Honestly I suspect either your meter being not accurate enough or the leads touching inadvertently trying to get at those close pins - but that’s just a hunch there.

I have had coils read 0 - they were definitely bad and popped fuses. Another check would be if you have an ammeter - your current should be somewhere around 5A. If it really is 0 ohms you will have a really high load current.

Here’s another pic showing the same coil reading voltage and current while energized.

V=I*R … so 12V ~~ 3.5 Ohms @ 3.5 A

 

[Alecnavarro]

Honestly I suspect either your meter being not accurate enough or the leads touching inadvertently trying to get at those close pins - but that’s just a hunch there.

I have had coils read 0 - they were definitely bad and popped fuses. Another check would be if you have an ammeter - your current should be somewhere around 5A. If it really is 0 ohms you will have a really high load current.

Here’s another pic showing the same coil reading voltage and current while energized.

V=I*R … so 12V ~~ 3.5 Ohms @ 3.5 A

New development. Friend brought better multi meter. Rear reads 4.2, front reads 0.00. Sweeeeett.

 

[Alecnavarro]

Honestly I suspect either your meter being not accurate enough or the leads touching inadvertently trying to get at those close pins - but that’s just a hunch there.

I have had coils read 0 - they were definitely bad and popped fuses. Another check would be if you have an ammeter - your current should be somewhere around 5A. If it really is 0 ohms you will have a really high load current.

Here’s another pic showing the same coil reading voltage and current while energized.

V=I*R … so 12V ~~ 3.5 Ohms @ 3.5 A

Appreciate all the info. I guess my next question would be, what are the odds it’s a bad wire or something fixable if I were to crack it open? Not sure I’m gonna get any help from Ford performance or if it’s possible to just buy a coil.

 

[Fasteddy]

The following two pictures are me testing the leads coming up directly from the locker. 0 ohms plugged in and open when unplugged. I’m not too savvy on the electrical side of things, maybe I have it on the wrong settings?

Change your meter setting to 200 ohms instead of 20K ohms, your meter is fine just not auto ranging so you have to select the appropriate range to get accurate results, or use an auto range meter...

 

[Alecnavarro]

Change your meter setting to 200 ohms instead of 20K ohms, your meter is fine just not auto ranging so you have to select the appropriate range to get accurate results, or use an auto range meter...

Above I posted that I tried with a different meter, that one was auto. Read 4.2 in rear and 0.00 front.

 

[Brian_B]

Appreciate all the info. I guess my next question would be, what are the odds it’s a bad wire or something fixable if I were to crack it open? Not sure I’m gonna get any help from Ford performance or if it’s possible to just buy a coil.

If you are checking the resistance at the diff itself, there is a chance it’s not the coil, but the likely culprit is the coil. The wiring inside the diff is only about 6” long and there is one pass-through wiring adapter. That’s about it.

It’s possible to buy just the coil. I’ve got a thread around here somewhere where I fixed mine - the Spicer part numbers are available (not Ford parts). It will also require pulling and replacing a bearing. Word of warning: Spicer parts are often on back order. That tread included part numbers and everything - will see if I can dig it up

There is a spacer plate on the coil - just a very small plastic ring on the bottom side. Make very sure to transfer that over to your new coil, it wasn’t very obvious in my case and it caused a lot of heartburn.

Now - all of that said - if it’s a brand new m210 from Ford, they should swap the entire thing out on warranty (it should have a parts warranty of 1 year) and I recommend that course, as you have to pull and reinstall the diff to fix this thing anyway.

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