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Fuseable link for alternator

DoctorPhate

NAXJA Forum User
Location
Ottawa Canada
My alternator is fine but its not charging, I was suggested by a mechanic that there is in line fuse for the alternator on my XJ.

Anyone know where this is?
 
You can add one, I dont recall there being one from the factory. Talk to 5-90 he has an awesome cable kit.
 
The only bolt on an alt that's going to have power is the stud with the power wire on it. All other wires are grounds that are used for energizing the coil field for different power outputs that are controlled by the ECM. I'd pull the alt. and take it to autozone or another store of the like and have it tested. They can do a bench test on it and tell you if it's charging and working properly or not. If it's working fine then I'd check the fuses on the main fuse block under the hood as I think there's one there that's for the alt.
 
I'm going to assume your rig is a 1992 - please let me know if it is not, as it changes things:

Just about every vehicle I've seen made in the last sixty years has had some variety of fuse to isolate the alternator/generator if there is a problem. This may be a section of fusible link wire or an actual fuses(s).

For your 1992, you should have a pair of MAXI50 or MAXI60 fuses in the PDC proper labelled "Generator." Check these.

If you want to check quickly, you can do so with the engine off. Simply check for +12VDC at the screwpost with the large black plastic surround - this is connected directly to the battery (via the fuse) - if you have +12VDC (nominal battery voltage) there with the engine off, the wiring is sound.

The two terminals with the common grey surround are the connections to the regulator for the field coils. The voltage here varies according to system demand, but it typically runs +0.5-4.0VDC. You won't get a reading here unless the engine is running. Watch your fingers! If you don't get a voltage signal at either post with the engine running (one is supplied, one is grounded,) you could be looking at either a wiring fault or a blown regulator (which requires PCM replacement - that's where the wretched thing is.)

One more once - as far as the "bench test" at Autozone or anywhere like that, they're checking for voltage at about one Ampere - which isn't really enough to fire a spark plug properly (and won't power a decent flashlight fully!) The little red rollaround Bear ARBST tester is more effective, but if you really want to wring your alternator you you should take it to a shop that does nothing but - they've usually got a bench that will check voltage output, peak current output, check for diode ripple, and just about anything else.

And please, for the love of Gawd and all you hold holy, do not RPT NOT "test" your alternator by getting the engine going and then disconnecting the battery! This generates HV transients, and can blow out important electronics (like control modules...) Suddenly, you've got problems to fix that you didn't have when you started, and you've just made more work for yourself in the space of thirty seconds. Brava!
 
The only bolt on an alt that's going to have power is the stud with the power wire on it. All other wires are grounds that are used for energizing the coil field for different power outputs that are controlled by the ECM. I'd pull the alt. and take it to autozone or another store of the like and have it tested. They can do a bench test on it and tell you if it's charging and working properly or not. If it's working fine then I'd check the fuses on the main fuse block under the hood as I think there's one there that's for the alt.

Uh, no, actually one of the small terminals receives power from the asd relay. No power there, no charge.

Of course as always on NAXJA, since the original poster didn't bother to inform us what YEAR the vehicle is, this is just an assumption. Using 96 data above.
 
All the fuses in the panel were good, we assumed it was the black module on the back of the alternator thats wired right into the vehicle, we had an extra so put it on. Just in the process of installing a brand new alternator that I had in my garage anyway.
 
On my 96 there's a length of wire coming off the power/fuse/relay block. If you wipe the crud off the thinner (mine's green) wire it says fuseable link on it. Bypass it for testing purpose only. You could replace it with a marine fuse of the same rating if that is available.
 
Unless the alternator output cable to the PDC has been replaced with plain cable, there will be a fusible link in it capable of handling the max amp of the alternator.

As the alternator output cable is horribly undersized, and should be changed out for a 4 ga cable, adding a marine-style fuse as noted above is the way to go, especially if you are upgrading to a high-output alternator.

Scroll down the page and check this article:

http://www.olypen.com/craigh/charge.htm
 
Unless the alternator output cable to the PDC has been replaced with plain cable, there will be a fusible link in it capable of handling the max amp of the alternator.

As the alternator output cable is horribly undersized, and should be changed out for a 4 ga cable, adding a marine-style fuse as noted above is the way to go, especially if you are upgrading to a high-output alternator.

Scroll down the page and check this article:

http://www.olypen.com/craigh/charge.htm

ANL fuses are probably easiest to find in a pinch - which is why I decided to use them (autosound people like to use ANL fuses, and they're easier to find than, say, MEGA fuses - and you don't have to "gang" them like MAXI fuses.)

Your 1997, if it has the two separated 8m/m screwposts, should have the fusible link going to the screwpost that is not connected to the battery. Fusible link wire is four "numbers" smaller than the circuit it's protecting - the alternator output lead is 6AWG (undersized,) which makes the fusible link wire 10AWG (which I haven't been able to find.)

Therefore, if it's blown, replace it with a high-amp fuse anyhow. Out of the various high-amp fuse profiles available, the ANL seems to be about the best: you can them locally, they're mechanically tough, they can be changed in about one minute using a 9/16" wrench, and they're generally available in ratings up to 250-300A (ANL fuses are made up to 600A, and I can probably find them that big if you really want them. I had a guy who wanted to fuse the feed for his winch - I looked up the model and the current required, and sourced him something like an ANL475...)
 
it ended up being the black module that attaches to the alternator. Replaced it with one I had laying around and she's good to go.

Btw I was posting for a friend. Mine is a 98 2dr w/ some stuff and his is a 97 4dr stock with BFG MT KM2s.

It was easier and faster to write in the first person since we wanted to get her done before we go wheeling today.

Thanks for the help though guys, you sparked the idea of the module for me.

Off we go wheeling now!
 
Uh, no, actually one of the small terminals receives power from the asd relay. No power there, no charge.

Correct. The ground side of the field coil is controlled by the engine computer. Time to start tracing back from the connector to see why it doesn't have power with the engine running. No check engine light? I thought the PCM would set a check engine light if the field coil didn't have power.
 
Correct. The ground side of the field coil is controlled by the engine computer. Time to start tracing back from the connector to see why it doesn't have power with the engine running. No check engine light? I thought the PCM would set a check engine light if the field coil didn't have power.

No check engine light. Like i said, turned out to be the alternator module
 
[FONT=&quot]The rule I learned years ago was to make the fusible link 4 wire sizes smaller than the supply wire.
If you are installing a 4-gauge alternator wire, it should contain an 8-gauge fusible link.[/FONT]
 
By "module on the wiring harness by the alternator" do you mean the black plastic part that screws onto the alternator? If so, as far as I know that's just a specialty molded connector to make sure you can't swap the field terminals accidentally.

Anyone know for sure?
 
Just remember, when you make something idiot proof the world makes a new idiot :D I'm sure somewhere out there (*cough* on jeeps unlimited maybe? *cough*) there is a thread by someone who has cut the wires going to it and swapped them because they thought it would fix their issue.
 
By "module on the wiring harness by the alternator" do you mean the black plastic part that screws onto the alternator? If so, as far as I know that's just a specialty molded connector to make sure you can't swap the field terminals accidentally.

Anyone know for sure?

More like "a specially moulded connector to have all the terminals located" - the field coil isn't polarised, so it doesn't really care which way it's hooked up (nor does field coil polarisation have anything to do with output polarity. Alternators generate AC voltage natively, whichis converted to positive DC voltage by the rectifier assembly. You'd have to reverse all of the diodes in the rectifier to generate negative DC voltage instead...)

It's just something that's there to make life easier for Zimbu the Monkey - just like the moulded rubber bit that locates the wiring on later model starter motors (if you can't tell the difference between the solenoid trigger lead and the starter motor power lead, you shouldn't be anywhere near a wrench alone!)
 
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