Alternator Questions
#1
01-10-2019, 12:07 PM
Join Date: Feb 2016
Location: Texas
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Alternator Questions
Hello All, I need some advice on an issue that started recently. My Alt light came on when I started the truck, after a while it went off, still appears to be charging battery. Then when the lights are pulled the head/tail lights flash and flicker and the alt gauge goes crazy, turn off lights no issues. this has been going on for about 3-4 weeks and I drive the truck around 4 days out of a week, during this time period the Alt light has only come on 2 or 3 times. I figure time to replace Alt, does this sound correct? I cant find a voltage regulator anywhere so I am thinking its internal, Alt came with truck so I dont know too much about it. 390 FE with MSD ignition and the only accessory is radio. Can I put in a 100 amp internal reg Alt or do I need to confirm and/or change anything?
#2
01-10-2019, 12:37 PM
Need to be careful to some degree about installing a high output alternator. Remember the trucks wiring itself is old, and was never designed to carry 100 amps. I don't know how many accessories and current hog drawing devices you have in your truck so it may not be a problem but it is something one should beware of.
Is the fan belt tight, cables in good shape and secure? Old corroded connections don't help. Run the idle up to 1800 to 2000 RPM and turn the headlights on and heater on HI. Then, measure the voltage at the battery posts. Should be 13.8 to 14.3, something like that.
Poor grounds are always a problem in old cars and trucks.
Is the fan belt tight, cables in good shape and secure? Old corroded connections don't help. Run the idle up to 1800 to 2000 RPM and turn the headlights on and heater on HI. Then, measure the voltage at the battery posts. Should be 13.8 to 14.3, something like that.
Poor grounds are always a problem in old cars and trucks.
#3
01-10-2019, 12:49 PM
Join Date: Feb 2016
Location: Texas
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Need to be careful to some degree about installing a high output alternator. Remember the trucks wiring itself is old, and was never designed to carry 100 amps. I don't know how many accessories and current hog drawing devices you have in your truck so it may not be a problem but it is something one should beware of.
Is the fan belt tight, cables in good shape and secure? Old corroded connections don't help. Run the idle up to 1800 to 2000 RPM and turn the headlights on and heater on HI. Then, measure the voltage at the battery posts. Should be 13.8 to 14.3, something like that.
Poor grounds are always a problem in old cars and trucks.
Is the fan belt tight, cables in good shape and secure? Old corroded connections don't help. Run the idle up to 1800 to 2000 RPM and turn the headlights on and heater on HI. Then, measure the voltage at the battery posts. Should be 13.8 to 14.3, something like that.
Poor grounds are always a problem in old cars and trucks.
#4
01-11-2019, 06:12 AM
Since all the wiring and the engine have been replaced, the alternator is unlikely to be a stock 65/66 alternator which was at best 55 amps. Unless you have an electric fuel pump with EFI and electric cooling fans, there is no need for a 100 amp alternator. Having said that, it could still be bad. You need to do more diagnostic testing to pinpoint the problem. You can take your alternator to almost any auto parts store and have it tested.
#5
01-11-2019, 07:17 AM
Logistics Pro
Ok I figure if its stock its 70amp, the all wiring from front to back is new motor has about 27000 on it, dont know the Alt history before I got itbut I put thi motor was put in after I got the truck, no Heater or AC and just the radio. I though the belt was a little loose but not enough to make noise, I will check that. Thanks for the suggestions.
A 45, 55 & 60 amp were optional. 60 amp included a ammeter and oil pressure gauge
Test yours to see what it its putting out.
#6
01-31-2019, 01:53 PM
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Ok my alt tested good at 65 amp and I found the location of the regulator and bought a replacement but it was only a 60 amp regulator and I was told it would be fine it would just out put 60 amp. There is no AC or heater, there is a electric fuel pump in tank and a simple radio and two speakers and I have a ammeter and oil pressure gauge in the dash. Voltage reg has worked great for about 3-4 weeks now I am back to flashing and dimming of lights after dark. I am just not finding a volt reg like mine for 65 amps so my question is would buying a new 60 or 70 amp Alt with the same volt reg maybe solve the problem?
#7
01-31-2019, 03:22 PM
Even a nearly invisible, paper thin layer of corrosion is enough to cripple the current output of any alternator. If the cables are original (or even just old) they need to be replaced. Grind down to bright shiny bare metal at block, frame, and firewall where they connect and tighten securely. Coat with vaseline or chassis grease, will keep pollution and road salt spray from forming corrosion as quickly.
Unless and until particular attention is paid to electrical connections and grounds in vintage & collector cars and trucks they will always have electrical problems. It's an issue with new cars and trucks too. It tends to roast switches (headlights use breakers, not fuses) and causes the flashing headlights, burns up regulators, diodes, stator rings, a reduction in starting and charging current and starves the ignition output.
Heat buildup from high resistance causes more corrosion, and more voltage drop, which causes even more heat, which causes more corrosion, till the connection fails altogether. Clean, tight electrical connections = Happy Electrons.
Here's some tests you can run to see the effect, all you need is a low ranging voltmeter. Works on starters, alternators, motors, headlights etc. Don't even need a wrench for this.
https://www.aa1car.com/library/voltage_drop_testing.htm
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#8
02-01-2019, 12:33 PM
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Most likely no. Sure, a Big *** Alternator might work for a while, but eventually you'll be right back to where you started. The fix is keeping the electrons you've already bought and paid for happy. Here's why. The problem isn't really the existing alternator or regulator, it is almost certainly the ground connections and cables, the headlight wiring, radiator support grounds, firewall block connector pins, etc.
Even a nearly invisible, paper thin layer of corrosion is enough to cripple the current output of any alternator. If the cables are original (or even just old) they need to be replaced. Grind down to bright shiny bare metal at block, frame, and firewall where they connect and tighten securely. Coat with vaseline or chassis grease, will keep pollution and road salt spray from forming corrosion as quickly.
Unless and until particular attention is paid to electrical connections and grounds in vintage & collector cars and trucks they will always have electrical problems. It's an issue with new cars and trucks too. It tends to roast switches (headlights use breakers, not fuses) and causes the flashing headlights, burns up regulators, diodes, stator rings, a reduction in starting and charging current and starves the ignition output.
Heat buildup from high resistance causes more corrosion, and more voltage drop, which causes even more heat, which causes more corrosion, till the connection fails altogether. Clean, tight electrical connections = Happy Electrons.
Here's some tests you can run to see the effect, all you need is a low ranging voltmeter. Works on starters, alternators, motors, headlights etc. Don't even need a wrench for this.
https://www.aa1car.com/library/voltage_drop_testing.htm
#9
02-07-2019, 05:50 PM
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One other thing that I did not see in these posts, is you might want to check your amp meter on the dash. My truck was doing basically the same thing. I found loose connections on the back side of my amp meter. I took it out and installed a volt meter instead in the same spot. I connected the 2 large #8 wires together and the problem was solved.
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