JDMClassic Posted August 30, 2014 Author Report Share Posted August 30, 2014 Looks like the fuses are good 1 Quote Link to comment
DanielC Posted August 30, 2014 Report Share Posted August 30, 2014 The truck may of originally had an externally regulated alternator. There is a really good possibility some previous owner changed it. If you just bought the truck, the alternator problem may be one reason it was for sale. I am not real familiar with 620 trucks. Other people on this board are. Now, if if was a 521... Glass fuses can look good, and be bad. The fuse element inside the fuse is just soldered to the end caps of the glass fuse. If the fuse gets hot, the element can come unsoldered from the end cap, and still look good. You must check for voltage on both sides of the fuse, with that circuit on. Use a test light. 1 Quote Link to comment
wayno Posted August 30, 2014 Report Share Posted August 30, 2014 When i went to autozone they told me that the stock alternator had an external regulator. But what I thought I had an internal... Yes the stock alternator for a 74 620 may have been externally regulated, but your alt. in the photo appears to be internally regulated if DanielC is correct, he mentioned in an earlier post if it had L/S on it, it was internally regulated, so someone likely changed it out. Now if that someone did not know what they were doing and just put that alternator on the engine and expected it to work, then they have not a clue, you see if and when you change over you have to make a set of jumper wires to bypass the external regulator like I did on my 521. This is what mine looks like on my 521, you can see the external regulator and its plug in back of my wiring mods. 1 Quote Link to comment
datzenmike Posted August 30, 2014 Report Share Posted August 30, 2014 Has S & L markings on it so internal regulator. 521 alternators were 33 or 35 amp depending before '71 620 alternators were 35 for L16/18 and 35 or 38 (optional) for the L20B engines.... internally regulated after '77. I think there is only one fuse that might prevent the alternator from charging . It provides power from the battery to one side of the red light. This is part of the sense wire providing a small current to start the alternator magnetic field. As the red charge light works it probably isn't that. You have two choices here. Convert to a internal set up by adding a couple of jumper wires and disconnecting your external regulator. or Replace the internal with an external regulated alternator. 1 Quote Link to comment
wayno Posted August 30, 2014 Report Share Posted August 30, 2014 This is what Daniel said in an earlier post, Take the alternator out. Look at the back of the alternator, by the two small terminals that are in a "T" orientation. there should be two other letters by that connection. If you have "F", and "N", it is an externally regulated alternator. "S" and "L" is an internally regulated alternator. So which version is correct, yours or his? Has S & L markings on it so external regulator. 521 alternators were 33 or 35 amp depending before '71 620 alternators were 35 for L16/18 and 35 or 38 (optional) for the L20B engines.... internally regulated after '77. I think there is only one fuse that might prevent the alternator from charging . It provides power from the battery to one side of the red light. This is part of the sense wire providing a small current to start the alternator magnetic field. As the red charge light works it probably isn't that. Otherwise put everything back together and see if it works!!! and we'll go from there. 1 Quote Link to comment
JDMClassic Posted August 30, 2014 Author Report Share Posted August 30, 2014 This is what I just picked up from pep boys... I'm trying to figure where is the ground connection is at tho 1 Quote Link to comment
datzenmike Posted August 30, 2014 Report Share Posted August 30, 2014 This is what Daniel said in an earlier post, Take the alternator out. Look at the back of the alternator, by the two small terminals that are in a "T" orientation. there should be two other letters by that connection. If you have "F", and "N", it is an externally regulated alternator. "S" and "L" is an internally regulated alternator. So which version is correct, yours or his? Yes wayno I read it and quoted it wrongly. Thought I corrected my mistake but missed that. Ah FIVE min between posts. You quoted me before I caught the mistake. S & L INTERNAL 1 Quote Link to comment
JDMClassic Posted August 30, 2014 Author Report Share Posted August 30, 2014 Yes wayno I read it and quoted it wrongly. Thought I corrected my mistake but missed that. Mike what gage you think that white and red wire to the positive connection of the alternator is? 1 Quote Link to comment
banzai510(hainz) Posted August 30, 2014 Report Share Posted August 30, 2014 If this is a 79 its a Internal volt reg reg truck. Im thinking 16, 14 gauge wire key is cleaning that burn up end before splicing it 1 Quote Link to comment
DanielC Posted August 30, 2014 Report Share Posted August 30, 2014 One or both of the bosses I put a black "circle" around should be threaded. That is the alternator ground connection. 1 Quote Link to comment
tr8er Posted August 30, 2014 Report Share Posted August 30, 2014 Does this wire potentially carry 35A? If so 90deg.C 14AWG cu conductor is minimum. What is it fused at? . 16AWG Is only good to 24A. 1 Quote Link to comment
tr8er Posted August 30, 2014 Report Share Posted August 30, 2014 If it's all metal, it's all common EGC ground. 1 Quote Link to comment
datzenmike Posted August 31, 2014 Report Share Posted August 31, 2014 Hello ratsun community. This is my situation. I just bought a 1974 Datsun 620 from a guy up in LA. After purchasing it I drove it back home in San Diego. Mike what gage you think that white and red wire to the positive connection of the alternator is? Does this wire potentially carry 35A? If so 90deg.C 14AWG cu conductor is minimum. What is it fused at? . 16AWG Is only good to 24A. Larger is always better. Fourteen is house wire and that looks much thicker. I would run 12 or more. The charge wire on my 100 amp alternator is thick as my little finger!!! Actually thicker than the stock 710 battery cable!!! 1 Quote Link to comment
tr8er Posted August 31, 2014 Report Share Posted August 31, 2014 I agree fully. My minimum was NEC code. Minimum is generally not wise. Wire is cheap. That said, copper the size of my finger (250 MCM) will carry around 400A. Maybe a compromise? 4AWG good to well over 100A. Durable. Workable. Available. Get THWN-2 or better. Fine strand. And it will still be enough when you upgrade your alt. 1 Quote Link to comment
JDMClassic Posted August 31, 2014 Author Report Share Posted August 31, 2014 If this is a 79 its a Internal volt reg reg truck. Im thinking 16, 14 gauge wire key is cleaning that burn up end before splicing it It's a 1974 with and L20b 1 Quote Link to comment
tr8er Posted August 31, 2014 Report Share Posted August 31, 2014 Looks like 6AWG. Possibly 4. 1 Quote Link to comment
JDMClassic Posted August 31, 2014 Author Report Share Posted August 31, 2014 So I'm charging my battery as we speak and in an hour I'm going to power it up. I've installed the Prostart alternator and gave the belt a tight tension. I've also replaced the charred section the wiring going in to the alternator.I think she's almost ready to be start up!! Fingers crossed and knock on elbows! Quote Link to comment
JDMClassic Posted August 31, 2014 Author Report Share Posted August 31, 2014 I 1 Quote Link to comment
datzenmike Posted August 31, 2014 Report Share Posted August 31, 2014 Never found out if you have an external voltage regulator on the inner fender. It's fist size and square metal can with rounded corners just behind the battery. I think it wise to check that it's there and plugged in. What if the truck has already been converted for use with that other internal alternator??? 1 Quote Link to comment
JDMClassic Posted August 31, 2014 Author Report Share Posted August 31, 2014 SHES ALIVEEEEEEE 1 Quote Link to comment
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