# help wiring dual batteries with an isolator



## myron585 (May 7, 2011)

hello,
I have a 1990 ford F-150 with a western uni-mount plow and I had alot of trouble not having enough power for the plow so I bought a 140amp isolator and I think i need help wiring it. I have it wired but I cant seem to find the right wire coming off the alternator that has the power. when I wired it I set up the second battery behind the seat and wired the plow stuff to the second battery and the isolator has the three post middle for the alt and the side post for battery one and two I just need to know if some can help me its going to snow big soon and I need it to work good.
thanks for you time.
myron 585


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## swtiih (Nov 30, 2008)

the thicker red wire coming off the back of the Alt. usually goes to a terminal strip on the firewall. 
This wire should go to Alt on the isolator. #1 goes to batt 1 & #2 goes to batt 2


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## 2COR517 (Oct 23, 2008)

You don't want an isolator for plowing. Just wire two brand new batteries in parallel with #2 cables.


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## Chris112lee (Nov 2, 2010)

You should also avoid putting wet cell batteries in the cab, as they release hydrogen gas.


I've even had a sealed AGM overcharge and release gas into the cab.


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## bossman34 (Aug 15, 2011)

myron585;1333116 said:


> hello,
> I have a 1990 ford F-150 with a western uni-mount plow and I had alot of trouble not having enough power for the plow so I bought a 140amp isolator and I think i need help wiring it. I have it wired but I cant seem to find the right wire coming off the alternator that has the power. when I wired it I set up the second battery behind the seat and wired the plow stuff to the second battery and the isolator has the three post middle for the alt and the side post for battery one and two I just need to know if some can help me its going to snow big soon and I need it to work good.
> thanks for you time.
> myron 585


Ya you need to listen to everyone. you should never put a battery in the cab as not only can they release gas they can explode. But about the isolator, adding that is a complete wast of your time and money. make a bracket and mount the battery under the hood and hook it up as if it were a diesel. I would run 2 gauge cable +to+, and -to-. problem solved.


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## fast*st (Jan 7, 2009)

Myron, 
The issue is likely your alternator, have it tested by any auto parts store. It is possible you have a 50 amp alternator that's barely able to run the truck with the heater and lights and all. I have an 89 250 that I upgraded to a 3G alternator (does your alternator have two plugs, one of the plugs having two thick wires on it?) My alternator would overheat often and stop charging or just melt, after the upgrade I have not had any problems. it requires a pulley swap and some very minor wire exchanges to upgrade. I used an alternator out of a Ranger or such, had the right clocking and 140 amp output(8 years back) and no troubles since. Look on Ford truck enthusiasts for awesome pictures and suggestions.

Now the rating on the stock alternator might be 65, but it'll only do that with a case temperature of less than 150F Underhood temps can run well above that and on a cold day with a high load, I was seeing alternator temperatures of 300F and above.


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## myron585 (May 7, 2011)

Fas"st thanks for your help. There are two plugs with the two black wire coming from the rectifier I hook that up to isolator and it didn't work and what you say makes a lot of sense and I Will move the battery to a new location out side I wasn't really thinking about the acid and the gases for that matter. The reason for the isolator is so the battery is for the plow only I already had a set up together in my last plow truck and I had always had a problem with one battery or the other not charging right.anyway all of the information I get from this site has always been awesome.
Thanks again everyone
Myron 585


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## fast*st (Jan 7, 2009)

Yeah, you have the 'standard duty' alternator. I would seriously look at upgrading it if you're going to be plowing and using an electric lift. 

The isolator is tricky, you get close to a 1 volt drop across the isolator, If your alternator is looking at output voltage it'll end up with 2 dead batteries, if your alternator references one of the isolated batteries, it may limit charging on the second one. Most times it will work fine if you can get the reference on the other side of the isolator and your alternator doesn't mind putting out 15.2 volts.

I think my alternator upgrade cost about $110 and they took my alternator as a core when I upgraded to the 3G unit from the low power one.


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