Unknown electrical issues
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Junior User
Joined: Dec 2010
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Unknown electrical issues
I drive a 1990 F-150 XLT Lariat with the 302, automatic 2x4. So battery is brand new and so is the alternator. Starter solenoid is newer. It is able to start up but once its been driven around or its sat somewhere for a while it needs to be charged before its able to start again. It's at 11.9V and drops to 7V when its cranking. One question I had was does the alternator need to be shocked? I was told it may need to be to set the direction of the polarity. Or what possible problems may it be and how do I test for them?
Cargo Master
Joined: Jan 2004
Posts: 3,118
Likes: 149
From: South Dakota
The old generaters needed to be polarized. That is something you definitely DO NOT want to do with an alternator. Possibly you have a bad battery, or was it acting that way before you replaced the battery?
Posting Guru
Joined: May 2007
Posts: 1,208
Likes: 2
From: North Reading Mass
A good fully charged battery should read 12.8 volts. Check and clean all of battery and alternator connections. Check the grounds too. With the engine running the voltage should be 1 or 2 volts higher than battery voltage. Mines holds pretty steady at 13.8.
The alternator doesn't have to shocked. Some old cars with generators would have to be polarized but none of the four I owned ever needed it.
The Haynes manual has a good diagnostic section that will save you time, money, and aggravation.
regards
rikard
The alternator doesn't have to shocked. Some old cars with generators would have to be polarized but none of the four I owned ever needed it.
The Haynes manual has a good diagnostic section that will save you time, money, and aggravation.
regards
rikard
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Junior User
Joined: Dec 2010
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I didn't get to drive it much before putting the battery in since there were a number of problems but one by one knocking them down! Slowly... But I'll try fully charging it and then I'll check the voltage as its running and I'll let you know! But won't the alternator charge the battery as its running? So if I jump it shouldn't it charge right up to max? This is my first truck I wanted something to fix up and I kinda got more than I was expecting 
By the way I have gotten the Hayne's manual. Thanks for the replies!
By the way I have gotten the Hayne's manual. Thanks for the replies!
Elder User
Joined: Feb 2008
Posts: 797
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From: ohio
test for a draw by removing neg terminal.Can use a test light or a volt meter,and connect it between the bat and neg terminal. Should barely light the light or on the volt meter .01.If it reads a large draw start pulling fuses and unplug alt till you find the draw. Also check that the sol wires are correct.
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Junior User
Joined: Dec 2010
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Hey deeznuts822 Thanks for the reply I did that and got 0.0 on the volt meter touching the positive terminal on the battery to the neg cable. I'm going to try fully charging the battery and hopefully that solves the problem just dont want it dying while im halfway in between work and home since I work 20 minutes highway driving from home...
Posting Guru
Joined: Jul 2006
Posts: 1,276
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From: Westminster,Md
Try " re-reading " deeznuts882's post,..sounds like what he is describing is the correct method for checking for a draw..but "your" description of how you did it is incorrect, ..
But your voltmeter will read 0.0v making the test you described..not trying to be a smartazz..just been a long day and trying to follow along.( or think things thru)
Remove the NEG batt cable..put the voltmeter leads between the" removed"" NEG cable and the" NEG Batt post"..should be less than.01-.02v..
But your voltmeter will read 0.0v making the test you described..not trying to be a smartazz..just been a long day and trying to follow along.( or think things thru)
Remove the NEG batt cable..put the voltmeter leads between the" removed"" NEG cable and the" NEG Batt post"..should be less than.01-.02v..
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Post Fiend
Joined: Apr 2004
Posts: 6,473
Likes: 4
From: Lafayette, IN
Sorry, guys, but putting a voltmeter between the negative cable and the negative battery post is a pointless test. You can do that with an AMMETER to check for a draw with the key off (you also need to pull the under hood light bulb).
First things first, though.
Check the voltage of the battery with the engine running. It should be 13.5-14.5V.
Next, check the battery voltage with the engine off, key off. That should be about 12.6V or slightly more. Anything under 12.5V is suspect.
Next, pop the vent caps on the battery, usually two nearly rectangular caps on top of the battery. Don't get the battery acid on you (wear rubber gloves, safety goggles, etc.--that's my disclaimer if you disfigure yourself messing with the acid). There should be a total of 6 holes that allow you access to the battery acid. You need to measure the voltage of them in adjacent pairs: 1-2, 2-3, 3-4, 4-5 and 5-6. Each of these pairs should measure about 2.1V. Any of them under 2V or significantly different from the others means you probably have a bad battery.
Start with those simple checks, then get back to us.
Jason
First things first, though.
Check the voltage of the battery with the engine running. It should be 13.5-14.5V.
Next, check the battery voltage with the engine off, key off. That should be about 12.6V or slightly more. Anything under 12.5V is suspect.
Next, pop the vent caps on the battery, usually two nearly rectangular caps on top of the battery. Don't get the battery acid on you (wear rubber gloves, safety goggles, etc.--that's my disclaimer if you disfigure yourself messing with the acid). There should be a total of 6 holes that allow you access to the battery acid. You need to measure the voltage of them in adjacent pairs: 1-2, 2-3, 3-4, 4-5 and 5-6. Each of these pairs should measure about 2.1V. Any of them under 2V or significantly different from the others means you probably have a bad battery.
Start with those simple checks, then get back to us.
Jason
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Elder User
Joined: Feb 2008
Posts: 797
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From: ohio
I have a dvm,but anyways i should have been more specific. You will want to go between the neg terminal you removed and the neg post on battery. You can get a digital volt\amp meter at harbor freight for about 5 bux. You will want to set it on amps,and its about the only easy way to find shorts. On my 88 I had similar issues to what your having and it ended up being the eec relay and its connector. 23 bux total fix from my local napa store.
Fleet Owner
Joined: Aug 2005
Posts: 23,666
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From: Easton,Ks
NEVER remove the any battery terminal with the engine running.
Without the battery the voltage can go well over 100 Volts and blow all the electrical items on the truck (Computer, radio, ....).
To check the alternator (AC generator in Fords) ground the "F" screw on the AC generator.
Then check for charging, if it charges the regulator is bad.
Also an AC Generator will not charge without voltage from the battery.
Without the battery the voltage can go well over 100 Volts and blow all the electrical items on the truck (Computer, radio, ....).
To check the alternator (AC generator in Fords) ground the "F" screw on the AC generator.
Then check for charging, if it charges the regulator is bad.
Also an AC Generator will not charge without voltage from the battery.