I have been having some charging issues.440 with a 60 amp alternator.I have dual electric fans.Would putting in a larger amp alternator help solve this problem?

Yes. What size fans do you run? Most fans I've seen take at least 10 amps, and some upwards of 30 to 45. They will be on at idle when your alternator is putting out its lowest charge. For a stock 60amp I think idle charge is around 35amp. Sounds like you need an alternator upgrade. Do you run heat, a/c? Stock headlights or halogen? Aftermarket stereo and amp?

depends on the charging issue, and how much more pull the fans actually have.

also your driving habits also determine if that is enough extra or you would have to step up to an even larger alt.

do you know how many amps both fans pull when they are on full? the manufacture should tell you.

if you spend your time mostly at idle, then the 78 amp might not be enough.
you might need to step up to one of the 120amp ones at idle type alt.

if however you mostly do freeway crusing or drive extended periods above idle, and they don't each draw 40 amps, then you might be ok with just getting a regular parts store 78 amp alt.


again that also depends on what you mean by charging issue.
if the fans only pull 40 amps together, and you have a dead battery every 2 weeks, you may have a different issue altogether.

I agree , just don't ASSUME a larger alt. is going to fix a problem.

Also realize you will probably need to upgrade your wiring on the charging circuit ... if you haven't already ...

What double R said #1 make sure EVERY terminal/connection in the car is clean/tight/good continuity. I would do Nacho's bulkhead parallel bypass (simple/easy/effective) & me I prefer to relay add ons to the alt to keep the ammeter honest & keep the extra current out of the bulkhead (you are feeding the extra devices right from the source-the alt). As said investigate whether a 78 amper from an 89 M body will be enough or if you need one of the aftermarket or other makes alt (Denso or GM) etc. there's 2 sizes of alt pulleys (you want the small one) & I'm assuming you have a 7.250" crank pulley

Where you pull power for those fans is important if running a stock wiring harness.

Stock mopar alternators SUCK for idle output. Horrible piles o'crap.

I build a wire around set up to get rid of any alt charge wires going through the bulkhead and into the cabin.

I run a set of dual electric fans on my Charger which have a 20 amp constant draw (40 amp start). All my bulbs (except dome light, trunk light, and license plate light) are LED now which makes a tremendous difference in the draw when the lights are on. Everything else electrical if pretty much stock. Here is what I found:

- OEM 60 amp alternator - major discharge at idle ~20+ amps with fans on
- 78 amp alternator - around 10 amp discharge at idle with fans on
- 100 amp "Tuff Stuff" alternator - breaks even at idle with fans on

These tests were with no headlights on and A/C off. When I have my A/C on and especially with the headlights on at night, I get a discharge with even the 100 amp alternator. Keep in mind that's worst case...I don't drive much at night...much less stay at idle much with A/C on, etc.

I ran a couple of weeks with the 78 amp unit and I would describe it as marginal. It may work in a pinch but you will be right at the edge if you idle much at all with the fan running. I am reasonably happy with my 100 amp unit as having some discharge a worst case (which rarely happens) is fine with me. My alternator also looks/drops in like a OEM unit which is important to me. I haven't seen a reason to want to go to a higher output unit yet considering headaches with fitting it, splicing wires, etc....and losing the factory look.

If you don't care about originality, running a 6-8ga wire from the charging stud to the starter relay stud (where POS battery cable connects) isn't a bad idea. Make sure you splice a fusible link in on this wire 2ga smaller than the wire itself.

If you don't pull this bypass wire, it is essential you tap the power for the fan relay(s) from the alternator charge stud (or close by). That way, the fan's current won't get pulled through the bulkhead connector and dash harness while the car is running.

Thanks for the replies !! Moparts is awesome ! I will try to better describe my problem. Optima red top battery reads 12.5 off. Running,the voltage was all over the place.Fluctuating between 13 and 15v. Like most people here i have a bunch of voltage regulators,ballast resisters,ecm, etc.I put on a new voltage reg and showed 14.5 running. I went for a ride and after 20 miles i came to a stop and the car died. Cranked very very slow and got it to start and limped home. Back in the garage running the car showed under 13v. As i would rev it would not climb over 13v. Am i correct in thinking my alt is dead? The only electric accessory i have running is the fans. No radio. I drive 99% of the time during the day. No lights or wipers. Will going with the 78 amp alt help me? Thank you very much for the help guys!!!

no, 13 volts shows some charging.
the issue may be the regulator, or sensing line voltage.

I too had jumpy voltage at idle and couldn't figure it out.
I put in a relay for the sensing voltage so it read directly from the battery instead of the regular line and it cleared up my charging issues.

If you check your voltage at the battery and at the sensing line and see a difference, that may be your issue.
remember to use the ground at the vr not the battery to check your difference in voltage.

typically that would cause an over charging issue on a single field vr, not sure what it does to a dual field, since both fields would read the reduced voltage.

but that jumping is not the same as having an undercharge issue. that is bad sensing line voltage or bad vr.

if you got the same 12.5 on and off, that would be a no charge state, which could still be the vr or alt.

under charge would be all your accessories running and not being able to maintain 14.5 volts.
but really you need an amp meter at that point to see if you are truly under charging.
most parts stores could run that test.
but I would sugguest getting your actual issue fixed first with the sensing line voltage.

Sounds like your wiring is marginal someplace. Once heated up underhood you are having voltage drop. Clean and check all the grounds, including taking them off and making sure paint or rust isnt impeding the connection. Also make sure all the ground straps are there. Lots of stuff can happen in 40 years. Look for crappy wires in the charging system in general. Maybe time to get a new harness.

If you dont care about originality, just ground the hell out of everything. Im talking about adding an extra heavy wire from the block to the chassis and smaller ones to the vr and ecu. That has ended issues on several cars i have been involved with.

#1 see if that batt is OK, with a regular batt you slo charge it up overnight then have it load tested. Not sure if you do anything different with Optimas? anyone? 70 up flat reg/dual field terminal alt or 69 & earlier box reg/single field terminal alt? "full field" the alt for 3 seconds max just long enough to take a voltage reading at alt "batt" stud to nearby alt case & have all lights/acc OFF & wouldn't hurt to run a jumper from alt "batt" stud to battery positive post (priorly have a known good batt fully charged) & until you confirm the integrity of the optima it wouldn't hurt to sub in a known fully charged batt from one of your other rides (nobody has just one). Lastly you might pull all field wires & with jumper wires connect batt to reg blue (ign) and reg green (fld) to alt field, (if 70 & up) batt to reg top terminal (blue) and to either alt field terminal and seperately connect the other alt field terminal to reg side (green) terminal then on either system: reg case and alt case both to batt neg post and alt "batt" stud to battery positive post with a 6 or 8 ga jumper. with a fully charged borrowed battery set idle at 2k with lights/AC/heater ON & see what you get for voltage at battery posts. You might not need to do all of this but take what you need & holler back with any news. EDIT dont ch the alt till we pin the problem