Head lights flicker
#1
Head lights flicker
My head lights would flicker while I had them turned on and my brother said my alternator, so I bought another "used one from a salvage yard". It did the same thing but if I hit the gas it stopped. Last night my battery light came on and my battery died. So I put my original alternator back on and it still don't charge. Could it be they both are junk now or is it something else? Please help.
#2
RF Veteran
iTrader: (1)
You need to get a volt meter to test the system.
key off engine off
Check battery voltage
Lets say it is 12.5volts
(under 12volts means bad battery)
On the back of alternator is a larger Black/Orange stripe wire, it may have a cap on it, remove cap and test for 12.5volts there, if no volts then a Fusible Link is blown.
There will be a 3 wire connector on alternator, unplug it, there will be a Yellow/white stripe wire on this connector, test it for 12.5volts, if no volts then a different fusible link is blown.
If Battery light is working then the green wire is OK
Check white wire that loops back to alternator to make sure wire isn't loose or broken at either end, this wire is not there on some newer alternators, it is internal.
If you have battery voltage at the above 2 wires(Black/orange and Yellow/white) and battery light is working then alternator is bad, period.
Flickering or dimming head lights at idle means at least one of the 3 fields in the alternator has failed, so alternator can't output engine voltage at idle RPMs, if you raise RPMs and lights work fine again that confirms a bad field.
Old alternator could have blown a fusible link when failing, which is why you need to test the wires.
A Fusible Link is a short wire that acts like a "slow blow" fuse, if there is a short the wire will heat up and separate without melting and causing a fire, these are used on alternators because there can be short high amp spikes in voltage that would blow a regular fuse instantly, the Fusible link won't blow just heat up then cool down after the spike.
key off engine off
Check battery voltage
Lets say it is 12.5volts
(under 12volts means bad battery)
On the back of alternator is a larger Black/Orange stripe wire, it may have a cap on it, remove cap and test for 12.5volts there, if no volts then a Fusible Link is blown.
There will be a 3 wire connector on alternator, unplug it, there will be a Yellow/white stripe wire on this connector, test it for 12.5volts, if no volts then a different fusible link is blown.
If Battery light is working then the green wire is OK
Check white wire that loops back to alternator to make sure wire isn't loose or broken at either end, this wire is not there on some newer alternators, it is internal.
If you have battery voltage at the above 2 wires(Black/orange and Yellow/white) and battery light is working then alternator is bad, period.
Flickering or dimming head lights at idle means at least one of the 3 fields in the alternator has failed, so alternator can't output engine voltage at idle RPMs, if you raise RPMs and lights work fine again that confirms a bad field.
Old alternator could have blown a fusible link when failing, which is why you need to test the wires.
A Fusible Link is a short wire that acts like a "slow blow" fuse, if there is a short the wire will heat up and separate without melting and causing a fire, these are used on alternators because there can be short high amp spikes in voltage that would blow a regular fuse instantly, the Fusible link won't blow just heat up then cool down after the spike.
Last edited by RonD; 12-06-2015 at 10:55 AM.
#3
Well I just got done testing both wires and they both had voltage in them. One had the same voltage as the battery and the one on the 3 wire plug had 10.5 - 11 volts either because I had key on and not running or not a good connection. Either way both have voltage in them and the wire that loops back to itself is connected from what I can tell. I guess I'll get a new alternator and hope that fixes the issue. Just can't believe both are junk but oh well.
#4
RF Veteran
iTrader: (1)
Salvage yard alternator should have warranty, I just got one a few days ago with 60 day warranty, it did work fine, but not when first installed.
The old alternator blew the 15amp Yellow/white wire's fuse, in 1994 models Ford used fuses not fusible links.
So when I started the engine with new(used) alternator installed I still had the Battery Light on.
Had 0 volts on Yellow/white wire so checked the fuse and it was blown, installed new fuse and charging system was working again :)
The Yellow/white wire is hooked directly to the battery's "+" cable, so should have same voltage as battery, you could have corroded connector.
Your battery's "+" terminal should have 2 wires coming off it, larger wire goes to starter motor, smaller wire to Battery Junction Box, the battery junction box is where both the wires you tested connect, so both should have the same voltage, battery voltage.
You may have had a bad connection or poor ground on meter, but I would retest to make sure.
The old alternator blew the 15amp Yellow/white wire's fuse, in 1994 models Ford used fuses not fusible links.
So when I started the engine with new(used) alternator installed I still had the Battery Light on.
Had 0 volts on Yellow/white wire so checked the fuse and it was blown, installed new fuse and charging system was working again :)
The Yellow/white wire is hooked directly to the battery's "+" cable, so should have same voltage as battery, you could have corroded connector.
Your battery's "+" terminal should have 2 wires coming off it, larger wire goes to starter motor, smaller wire to Battery Junction Box, the battery junction box is where both the wires you tested connect, so both should have the same voltage, battery voltage.
You may have had a bad connection or poor ground on meter, but I would retest to make sure.
Last edited by RonD; 12-06-2015 at 06:15 PM.
#6
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