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Discussion Starter · #1 · (Edited)
I’ve read just about every thread in RCC about this subject, enough to make my head spin. But I still have a couple questions. So hopefully you guys have some patience.

1) How do you determine what your alternator is rated at?

2) When you upgrade your alternator charge wire, does it matter how big you Go? And do you size your fusible link/fuse to the wire size or to the max output of the alternator? I have 8AWG and some 6AWG and I’m trying to figure out how to size the the fuse/fusible link

3) everybody has seen the MAD electrical diagram. First thing that struck me is...Is there any reason why the two wires coming from the dash need their own power source? If they are tied together in the dash, can’t you supply power to one or the other? I read of somebody who did this and just dead headed off the other side. This seems like the best plan to me. What is the consensus?

4) some guys say run the bypass to the starter relay, a few have run it straight to the battery. If you are running a fuse/fusible link, does it matter?


Appreciate whatever help you guys can provide. I’m probably overthinking this issue, it’s a problem I have :)
 

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There is no need to do the bypass on '80s model trucks.
 

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1) big and squareish = 100 amp, small and round = 60 amp (or 40 amp)

2) when swapping 60 to 100 I've used the existing wire. as in: the factory didn't run smaller wires with the smaller alt. Pay attention to the grounds - the 60 ground through the mounting brackets, the 100 has rubber bushing and needs an external ground connection.

3) haven't looked at the diagram recently

4) The battery lead at the starter relay makes a great binding post. When I add relays for aux lights, I hook the switched power feed there with a ring lug. Electrically it's the same as tying to the battery because other end of the bat cable. Physically it's an easier connection.

5) what Elwenil said. The entire point of the mod is to bypass the ALT gauge on tin grilles because when the gauge eventually fails the entire truck goes dark. 81 and up don't have this problem because the factory changed the wiring. I've found that simply connecting the (2) alt gauge leads together (bypassing the gauge) and clean up the bulk head connector is sufficient .
 

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yup THROW the diagram from MAD away as it does NOT pertain to your truck / its just confusing you

all Chrysler Alts are marked on the case as to AMP output / also there not all marked in the same spot

617069
 

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Discussion Starter · #5 ·
I knew my truck had a shunt ammeter, but I wanted to bypass it anyway. Having had 80s trucks with finicky wiring before, I wanted to reduce the load and maybe avoid some possible problems in the future.

I also want to add a bigger alternator in the future and want to have adequate wiring for that.

Im now more confused because I read there was a 60, and a 70-something alternator in the same case? Is the 100 the bigger police style alternator or is that the same square case also?

Battery or relay post doesnt matter. Got it. Anybody got any input on how to size your fusible link? Is it sized to the wire or to the alternator? I read the Allpar links on the subject and they have recommendations there but not quite clear to me how they came to that
 

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Changing the wiring from stock that isn't going to improve anything may just cause problems down the road since no wiring diagram will make any sense anymore. If it ain't broke, don't fix it. If you really want to "fix" wiring issues, rebuild the harness using marine grade tinned copper wire of a larger gauge than original and sealed terminals where possible. Nothing else is really going to make much difference. For a larger alternator all you need is to run one large cable from the alternator output to the positive terminal of the battery, gauge will depending on the output of the alternator.

Alternators can be rebuilt to various specs, but you can have a 70A alternator with the normal small case. Don't expect any parts store alternator to come anywhere near any sort of stock rating, especially at idle. The 100A-140A Chrysler alternators are all larger housing and require special brackets. The easiest upgrade for an older truck is a late '80s Nippondenso 90A-120A alternator with the V-belt pulley which should bolt in the stock brackets if you get the right one.

Fusible links are sized to the wire gauge. The wire gauge is sized for the amperage of the circuit.
 

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Discussion Starter · #7 ·
Running the charge wire directly to the relay or battery is going to reduce the load going through the bulkhead. That alone seems like a worthwhile upgrade, no? I'm going with a voltmeter anyhow, so it's a moot point. But even if we left the ammeter in place, it seems like a good thing to do.

I'm not under any illusions that a parts store unit will be putting out what the factory unit is capable of. I had planned on upgrading the alternator via a rebuild kit rather than a parts store unit. I had seen links posted to aftermarket upgrade kits, that seemed like a good solution. Agreed I could always go with the Nippondenso unit as well. In fact, that might be the best route. What years were the Nippondenso alternator with the v belt pulley used?

Now, the reason I was confused about sizing the wire, is because I'm seeing differences in wire ratings. This link here shows a different capacity than what Allpar says:

Vs.


I'm going to use either an 8 or a 6 AWG. According to Allpar, if you were putting out 85 amps, you would need an 8AWG, but per the first link 8 AWG is only good to 55 amps. Similar story with 6 AWG...Allpar says its good for 100-120 amp alternators, but the chart says it's only good for 75. Which set of data is correct?


And that is also why I was asking if the fusible link needed to be sized to the wire or to the alternator output. Glad you cleared that part up though. I appreciate the input.
 

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On the 80's trucks, the charge wire already runs close to directly to the battery (by way of the firewall). The ammeter uses the charge wire as an external shunt.

That first article is a bit whacky, I will have to study it a bit to see what they are trying to say. A wire carrying 6 volts, needs to be twice the area of the same load at 12 volts. and 24 volts only needs 1/2 the area, yet they treat them all the same.

You need to think of where the load you want to deal with, is at. For example, a winch wired to the battery, can easily be covered by running a proper wire right to the battery. But a super stereo, with a super powered amp, in the back of the RC, will not work so well.

Some here will disagree, but I run a big wire straight across the engine, to the battery, with both winches hooked directly to the battery, Through big switch's, to cut power to the winch's when I do not use them.
 

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Discussion Starter · #9 ·
I'm expecting a FSM in the mail soon, so I'll be able to verify myself. But are you saying the charge wire doesn't go through the bulkhead? I also don't have the truck in front of me so I can't look, but I will trace it out when I get a chance and verify.

I just used that link as an example. I pulled up a couple different ones in recent days with conflicting information.

The load will be in or on the truck. Some additional lights, a CB, maybe a modest stereo. Possibly an electric fuel pump, and long term....maybe an air locker which would need a compressor right? I don't see a winch in my future but you never know. The point here is, I want to be prepared for whatever I might add.
 

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Only on the '70s and earlier models does the charge wire take a detour into the interior to go through the Ammeter. I will say that running a cable directly to the battery when I upgraded my old '84 Ramcharger made the Ammeter useless. It pointed dead even from then on and did not show a charge or discharge. Not a huge deal since the Ammeter is not that useful to begin with.

Keep in mind that you really don't need a huge alternator to keep up with random draw from intermittent devices. An alternator needs to be able to keep up with the max draw of all the normal things a vehicle uses. Worst case scenario for most vehicles would be sitting on the side of the road at night with the hazard flashers on with all the lights, heat or A/C and wipers on. Something that occasionally draws power like an air compressor will use the battery as a cushion if it exceeds the maximum output of the alternator. A smaller alternator will simply take longer to refill the battery to full charge.

As for wire diameter, I would go with whatever the factory used for a similar setup. I think the old 140A alternators used something like a 4 or 6 gauge cable. You will get conflicting info on wire ratings due to the type of wire and the quality, as well as the industry using it. What may work fine for a given application in a automobile might not jive with some industry standard for another application. My winch will draw more current than the 4 gauge cables I have running it, but I would have to run it at max pull for more than a few minutes to overheat them. As it is, the worst pulls I have used it for have not even made the terminals warm though the motor does get a little warmer. I am mindful of the age and duty cycle of my winch and I don't pull with it for more than 30 seconds at a time without a pause. The brake on my worm drive cannot break like a modern planetary winch so I use it with impunity. 😁
 

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Discussion Starter · #11 ·
Good stuff to think about, thanks.

If a guy wanted to use a fuse instead of a fusible link, how would you go about sizing that? Still sized to the wire?....say just under the max capacity of the wire?
 

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Here's a table with wire diameter vs curent and length.
8b2218f619ae068a449b8cac1eaee894.jpg
 

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I'm going to use either an 8 or a 6 AWG. According to Allpar, if you were putting out 85 amps, you would need an 8AWG, but per the first link 8 AWG is only good to 55 amps. Similar story with 6 AWG...Allpar says its good for 100-120 amp alternators, but the chart says it's only good for 75. Which set of data is correct?
here is right out of a 1984 FSM from Chrysler and its the ONLY info l would go by/ 100 amp uses a 6 and a 60 amp uses a 10 AWG wire , so in theory a 80 amp would use a 8 / also from the FSM is a 6 gauge fusible is good for 150-175 amp Alt

some light reading for you

 

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I'm expecting a FSM in the mail soon, so I'll be able to verify myself. But are you saying the charge wire doesn't go through the bulkhead? I also don't have the truck in front of me so I can't look, but I will trace it out when I get a chance and verify.

I just used that link as an example. I pulled up a couple different ones in recent days with conflicting information.

The load will be in or on the truck. Some additional lights, a CB, maybe a modest stereo. Possibly an electric fuel pump, and long term....maybe an air locker which would need a compressor right? I don't see a winch in my future but you never know. The point here is, I want to be prepared for whatever I might add.
Correct, the charge wire goes to the firewall, then over to the battery. Two wires are attached at strategic points, and go to the ammeter. That way the charge wire itself is used as an external shunt, and very little current has to go through the firewall, and gauge. To upgrade the wire, and still have the ammeter work, you would have to do a bunch of calculations, and attach the wires at the right distance apart on the new wire.

There is a lot more that goes into wire selection, then just what is done on the charts. they are just good estimates, and generally will work just fine. You can never go wrong with a bigger wire diameter.
 

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Discussion Starter · #15 ·
I'm getting rid of the ammeter and going with a volt meter anyhow, so that part isn't really necessary.

I appreciate the pointers, guys.
 

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Discussion Starter · #16 ·
UPDATE

I think I'm going with the Denso style alternator. So I have 2 questions:

Is this the alternator that works with the factory bracketry? I saw this part number posted elsewhere, I just wanted to confirm. Seems like there are a lot of options when it comes to late 80s and early 90s mopar alternators. This one looks right and has the v pulley.


The other question, I read elsewhere that the ammeter bypass is required if going to an alternator this big. But since I am working on an '84, is this unnecessary being it's a shunt ammeter? Should I disconnect the ammeter anyway?

I have not upgraded the charge wire yet, that will be done also.
 

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Discussion Starter · #18 ·
I didn't think my '84 has a PCM? I don't think those links pertain to what I'm trying to do.
 

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Correct, '84 won't have a PCM, which makes it easier. (PCM guys are trying to emulate the non-PCM setup.) All you need is an ignition-on feed; or use an ignition-switched relay to accomplish the same.
 

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it was posted to show different setups , but the wiring is all the same
 
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