I am trying to get my my car ready to take to the track this Friday. But now i have a alternator/charging problem. Here is what i am using.

2 red top optima battery's
remain 75 amp factory stile alt
new stock stile voltage reg
rewired alt

I used 1/0 gauge wire for both the battery grounds and the bat + wire running all the way to the start relay.
I have the blue wire on a switched 12 volts source going to the voltage reg then to the alt and the green wire going from the alt to the other side of the voltage reg. I am using a 6 gauge wire for the main power wire coming off the alt to the starter relay. I have a 4 gauge ground wire on the front of the engine going to the K frame and a 10 gauge wire on the back of the engine going to the fire wall. So i think i have everything wired up right.OK now to my problem.

When i start my car with the engine cold and running only the electric fuel pump and water pump. My car alt will put out 14.5 volts at idle and this is checking the voltage at the battery's.But when i turn on my 98 ford thours ( spelling)colling fan with the engine at 150 degrees my voltage will drop down to 12.3 and stay there. What i am trying to say is when my engine gets to operating temp my alt will not charge any more. Even if i turn the fan off. I hope that makes since. SO what could be wrong with my car?? IS 75 amp not just big enough to run my electrical loads now? OR do i need to add a ground at the alt?? I want to put a 100 amp one wire alt on my car but do not have the cash right now. oh for got to say i am running the stock size alt pulley and a march under drive crank pulley. But i do have a stock size crank pulley i can try if you think that will help. Thanks Mopar65

With the engine up to temp and the fan off does the
voltage come up if you bring up the rpm's... did you
try to full field the alt

If your still running the factory ameter I would bypass it and see how that effects things.

Mike if i rember right after the engine is warm and i reved it up to 2500 and it only showed 12 vots on my volatge guage. when you say full field. you are talking about pulling the green field wire off the alt and running a wire of the alt field to straight ground? if so i will try that tomarrow. thanks Mopar65

you got to get that reg off of there,bypass the ammeter too,i did the 85-92 forrunner 85 amp alt conversion (440 source.com)charges its butt off,and alot less clutter-jeff

good advice but i have rewired the alt/ing in the car so amp guage for me.thanks Mopar65

well my plan was just to run it this way until i get the money to convert it to a 100 amp one wire alt. But it will be awhile until i get the money to do that. mostly just run the factory stuff for now so i can get some racing in. also i have all ready got ride off all the factory wiring and rwired the car my self. thanks Mopar65

You said you had a Ford cooling fan? A Ford part. There's your problem. How much current is that fan supposed to draw? And how much current does it actually draw? You could stick an ammeter in one of the fan lines and find out. Go to a bolt on flex fan or clutch fan maybe - no current draw.
Have fun !

I run the 2 spd Taurus fan too...and it moves some major air. But it also pulls MAJOR amps. I tried running mine with a stock alt with no luck at all...especially on high. It pulls 30-35 amps...which is likely most all of or even more than your current alt makes at idle.

I upgraded to the powermaster 140 amp alt (makes 80 amps a idle) and all problems are gone. My feeling is your alt is just not up to the task...you need a bigger alt that also makes lots of amps at idle. Peak amps are less important than idle amps in my opinion.

i looked up 4 ruuner alt on ebay,a guy out in cali,bult me one in 85 amp.the one wires are good for boats or at the strip ,but if you drive on street,they dont like to charge at low idle,the 440 source conversion uses small alt,built in reg,i even run an idiot light on my volt meter with this system,hhr fan,electric water pump and csr water pump,-jeff

oops electric fuel pump and csr water pump

thanks for all the help guys and no i am not useing the factory amp guage anymore. Rob do you have a part number for the alt you are using? WAs that alt a bolt on deal or did you have to mod the alt brackets to get it to fit. also rob could you post a pick of it mounted on your car?

what i still don't understand is my car will put out 14.5 volts at idle with everything on except the fan. but as soon as the engine gets warm it will quit charging with the fan on or not and by that i mean my volts go from 14.5 down to around 12.5 with fan off to 11.9 with the fan on.now when my engine is cold like right after i just start it. I will have 14.5 volts at idle.then turn the fan on the volts will drop down to around 12.8. I to think i just do not have a big enough alt. just trying to figure out why it acts the way it does between a cold engine and a warm engine. thanks Mopar65

sorry mike i have not got to test the alt yet. Home sick today. so if i get to filling better i might try it today.I will let you know what i find out.thanks Bobby

With Mr P , when the load is removed ,when you turn off the fan, the volts should rise if your charging system is working right, You may also want to check for a high resistance circuit running from the alt output to the batts, A quick & easy way is to feel the output wiring for heat starting @ the alt thru all the connections back to the batts or a voltage drop test point to point to the batts

When the regulator sees the current(voltage?) drop from starting it allows the alternator to charge the battery up until it reaches the voltage your seeing(14.2 or? Once that level is reached it allows the battery to drain down until it SHOULD kick back in and raise the voltage up to 14.2. I would look real close at the regulator, it will heat up components inside and that may be the problem

With a external reg you should be able to test the alt by full fielding < apply more than 12 vdc to the green reg wire feeding the alt> the voltage should jump to over 14.5 vdc , that will tell you if its the alt or voltage reg, I am not that familiar with mopar alts < they dont use them on boats> but they are all on the same principal