Voltage drop after extended drives.

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Vacaville, CA
The truck...85 fj60 with original motor but now has a 200 amp mean green alternator and I love it. The truck has had this little gremlin with or with out the new alt. but have never really noticed it as much till tonight. Typically ill get 13.9 at the alt but there's a half volt drop to the batt right off the battery at 13.4-13.5. However after a 20 mile drive back with my HIDs fogs going and stero blasting I noticed the gauge was reading under 12.0 volts I confirmed this with my DMM.

I've noticed when I hot start the truck the seat belt light or maybe it's a part of the ACC. check does not always come on and the truck will not idle. Ill then have to cycle the key one or two more times till it does and when it does come on I know the truck will start and idle fine. Whether it has any relation to the first problem stated I'm not sure...you guys be the judge with your infinite amount of wisdom.

The question is do you guys or have had similar problems and what can be done to rectify this. These are intermitant but annoying. After letting the truck sit and cool down voltage stabilized at 13.8-13.9.

Also are all the green OE clips necceassary or can I just run a new set of thicker gauge wise to to harness and maybe a thicker wire from the alt. to the batt.?
 
What gauge wire from the alt. to the battery? Wire will have a resistance to any flow of current, you will easily see that half volt drop if the wire is too small.


Jerry D.
 
sounds like increased resistance in the wiring due to heat.
 
^ Exactly! If you're a 10 gauge wire from the alt. to the battery, at 100amp draw, you will have at least a half volt drop. Add to it the increased resistance due to heating/amp load, that will increase.

Jerry D.
 
The mean green alt. uses the original Toyota factory plug so as far as what gauge of wire goes its al OE.
 
And what, 30 years old?

Stock harness was inadequate for the mean green stock, It's even worse after a ton of time. Start upgrading wires..
 
With lights and killer sound, and that alt. that puts out 200amps, you should think about a 4 gauge wire from the alt. to the battery. At five feet of #4, you will still get a slight loss, about a quarter volt.
In this case, larger is better...

Jerry D.
 
Check all of the ground connections, remove and clean them and reinstall. If you are at 12 volts you are near dead in the battery department. How old is the battery? How many watts is the stereo system? Watts of the lights? Put your DMM in series with the circuit and crank the lights and stereo and see how much current you are pulling. Might use a shunt to do this. Check the resistance of the wiring, half a volt is quite a bit for such a short run.

Electrical gremlins usually are loose, corroded connections, or intermittent grounds.
 
^this...so what is the best course of action to attach a new thicker lead from the alt. to the batt.? Do I add to if so and keep the original plug and how so? Maybe I should get in touch with mean green, I'd rather not void and kind of warranty offered. I'm really curious to see how long the new alt will last.
 
Ground

Did you replace all the ground wire to a bigger gauge than what's in the vehicle? I'm not sure if it was suggested.:)
 
Look at the battery cable that goes to your starter. It most likely a 1 or 2 gauge cable, the starter most likely draws 150 to 250 amps during start. You MG alternator can deliver up to 200 amps to your battery, the cable from you alt. to the battery needs to be just as large.

I use 1 gauge from my 220 amp alt. through a 200 amp fuse near the alt. and to my battery.

I ASSUME the stock 60 amp alt. wiring would be about a 10 or 12 gauge wire. IMHO, you have been lucky the stock wire has not failed as yet.

Look here: http://www.bulkwire.com/wireresistance.asp

Jerry D.
 
Check all of the ground connections, remove and clean them and reinstall. If you are at 12 volts you are near dead in the battery department. How old is the battery? How many watts is the stereo system? Watts of the lights? Put your DMM in series with the circuit and crank the lights and stereo and see how much current you are pulling. Might use a shunt to do this. Check the resistance of the wiring, half a volt is quite a bit for such a short run.

Electrical gremlins usually are loose, corroded connections, or intermittent grounds.

Battery is about 6-7 year old optima yellow top...before they were bought out. I'm pushing a 900 watt amp for highs and 250 preamped sub. Lights can draw 10 amps up piece under start up but level out around 4-5.


Stock wiring just failed at the fuseable link so to anyone they sees this I am in need of one now however it finally caused me to upgrade to a 4 gauge wire for the alternator to the battery and problem solved.
 
Make sure you put a fuse into that 4 ga wire. It's rare but possible for an alternator to short, in which case that wire will melt/burn/possibly cause a fire.
 

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