Charging system problem 94 f150
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Joined: Mar 2003
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From: Detroit suburb
Charging system problem 94 f150
The guys in the other forum have helped - with one of the problems - found a broken wire under relay for EEC. Now runs but have a problem with charging. (Mine has the 3 wire going into alternator with 1 large hot wire and 1 other wire). Gauge is indicating about 10 amps, tested at local Autozone - they confirmed at about 11.3 to 11.6 amps. (This truck is a 94 f150 5.0 4 wd). Anyways it appears that there may be a problem with the gauge or the rheostat ? that may be a part of it. Red wire (green stripe) going to it has 12 volts, Green wire (red stripe) coming off of it - and going to alternator has only .8 to .9 volts. It is supposed to be hot in run or start position (I would assume 12 volts normal). Wondered if anybody else had this problem and what the fix was ? May require a new instrument cluster, hope not .....
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From: Virginia
What conditions was the 10 amp reading taken, and were was it taken at? If the battery and truck only need 10 amps, then that is all the alternator will supply at that time.
What other problems are you having? The best test for the alternator is a voltage test on the battery with the engine running. If you have around 14 volts with the engine running, then you are ok.
What other problems are you having? The best test for the alternator is a voltage test on the battery with the engine running. If you have around 14 volts with the engine running, then you are ok.
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From: Detroit suburb
Dave F:
The readings were taken with the truck idling and up to 2000 rpm. I agree 14 is about right, 10 is not good - test machine indicated taking about 1.8 amps from battery to keep running .... Nobody is answering the wiring question - which seems to be where the problem is originating. On the alternator 3 wire setup - yellow is always hot (12 V), and this green with red stripe that routes from the charging gauge is supposed to be hot in run or start position (I am assuming 12 V - I am getting less than ONE Volt) ..... there has already been a wire spliced in from under the dash to close to the right firewall - this Exact circuit - so apparently there was a problem once before. However, I NOW have a problem before this splice.
The readings were taken with the truck idling and up to 2000 rpm. I agree 14 is about right, 10 is not good - test machine indicated taking about 1.8 amps from battery to keep running .... Nobody is answering the wiring question - which seems to be where the problem is originating. On the alternator 3 wire setup - yellow is always hot (12 V), and this green with red stripe that routes from the charging gauge is supposed to be hot in run or start position (I am assuming 12 V - I am getting less than ONE Volt) ..... there has already been a wire spliced in from under the dash to close to the right firewall - this Exact circuit - so apparently there was a problem once before. However, I NOW have a problem before this splice.
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From: Detroit suburb
Ok, an update - someone suggested that I change the plug going into the alternator - did that but no change in outcome ..... the problem remains .....
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From: Virginia
I didn't understand what the wiring was you were talking about. Most trucks have a "alt" light in the dash, and that is where the green/red comes from to go to the alternator. If you have about 12 volts on the green/red at the alternator, then the light in the dash does not burn, and everything is supposedly ok. If you have a low voltage at the alternator green/red, then that's bad and the alt light in the dash burns.
Here's a diagram.
But I was wondering if you were charging at all. I wanted you to check for voltage at the battery which should be around 14 volts. The 10 you were talking about is amps correct? That's a different measurement, which I believe does not mean anything, so long as you have the correct voltage at the battery.
Here's a diagram.
But I was wondering if you were charging at all. I wanted you to check for voltage at the battery which should be around 14 volts. The 10 you were talking about is amps correct? That's a different measurement, which I believe does not mean anything, so long as you have the correct voltage at the battery.
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Joined: Mar 2003
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From: Detroit suburb
Dave F:
That is the correct diagram, mine is a 94 and it doesn't have a light - it has a gauge. Yes the references to 10 and 14 in posts above relate to volts I believe. The question now might be - which way does the current run ? I believe it might be From the ignition switch Red wire/green stripe to alternator (gauge), then from that point green wire / red stripe to alternator. What wire gives the internal regulator the signal to provide more/less charge to the battery ?? I cannot tell from the diagram (and not sure if this is the one responsible for that) ..... Right now the signal from the green wire/red stripe to alternator is .8 or .9 volts.
Thanks again
That is the correct diagram, mine is a 94 and it doesn't have a light - it has a gauge. Yes the references to 10 and 14 in posts above relate to volts I believe. The question now might be - which way does the current run ? I believe it might be From the ignition switch Red wire/green stripe to alternator (gauge), then from that point green wire / red stripe to alternator. What wire gives the internal regulator the signal to provide more/less charge to the battery ?? I cannot tell from the diagram (and not sure if this is the one responsible for that) ..... Right now the signal from the green wire/red stripe to alternator is .8 or .9 volts.
Thanks again
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If you are only getting 11.3 to 11.6 volts to the battery, your alternator is bad. dont always trust your local auto parts store's testing equipment. But if you know 100% that your alternator is o.k. it could be the larger wire from the charge post off the back of alternator (may have some corrosion in it). above all remember to keep it simple. the biggest problems could be the easiest fix.
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From: Virginia
You say you think the green/red wire is not getting voltage to trigger the alternator to charge. I would take a short piece of wire and jump the green/red to the battery + and see if it will charge.
Always good to make sure you are looking in the right area, and everything else is working ok.