Finally got 3g hooked nothing no power any where. Put on old alternator and voltage reulator starts up fine. Did some errands get home try to start later low on power. Got both alternators checked out both bad. They only had one 65 amp and that was only putting out 11 to 12 volts. Only one they had so I figured it would get me thur the weekend till they got another monday.

Notice when i disconnect the neg. battery terminal engine dies. I want to look at it tomorrow where should I start, thanks.

 

Ummmmmmm.. it's the positive cable you wanna pull to determine if the rig can stay running off of whatever the alternator is putting out.

I don't recommend doing it.

 

How else can I check the output for the alternator. Where should I start checking for a short. (assuming a short somewhere) Thanks

I know its not smart to pull cable from newer cars what problems could it cause on these old non digital trucks. (Assuming you don't do it alot) Just trying to learn something. Done alot of work to this truck but still new at all this stuff, got most things fixed thanks to board members.

 

While running, put a screwdriver up to the back of the alternator (in the center where it rotates) to see if a magnetic field is generated. Still, it doesn't verify that it puts out adequate current.

Pull it and have it tested. Btw, go to a part store where you can direclty observe the readings. They'll do anything to pad their sales.... one place I went to said it was bad and the other place lost their harness adapter.

I ended up swapping the 3G into my 73 (which I already retrofitted) to verify it worked.

 

Yea thats why did not get the 3g tested first, 2 week old machine and they could not find the plug. I think I may be blowing alternators Like I said the one i have on now has low voltage output. They could find the plug for that one either. I had to put it on the truck so they could take a voltage reading. Thats the reason I pulled the cable to see it would stay running. Did not want run to parts store only to run out of bat. power and no alternator.

I did put in a variable wiper control switch from a 70's truck before this happened. Also had problems with the pigtail but put in a new one before this started to happen. Delay switch is a great easy upgrade by the way.

 

Removing a battery cable while running with an alternator can send voltage spikes over 100v. More than enough the fry alternator or regulator. Battery should read 12.5v at rest, when properly charging 13.5-14.5v depending on load. If a new 3g is not charging, I would suspect it being wired wrong.

 

Ok thanks for the info. 3g not new but junkyard, headed there right now to get another. When I get back I'm going to tear into it. I'm thinking I might just pull harness from under dash kind of a mess from po.

Is there a way to check voltage output from alternator without bring it to auto parts store. I hate to put a good one on only to ruin it.

If I check voltage with a meter and it has 13 + can I asume it is charging, safe to drive to parts store?

 

If you are reading 11 to 12 V, the alternator is not "putting out" anything. You are just reading the battery voltage. Does your truck have a seperate voltage regulator on the radiator support? If you are only using the alternator with a built in regulator, then you either have it wired up incorrectly or the alternator is bad. Not really any other things that can cause your symptoms.

 

Hey 360,
You got all the right plugs and stuff to do that job? Why don't you hop on the net and google 3g wiring to get a quick look at the diagram. Sounds to me like something that's suppose to be hot isn't getting hot. You know the 3g has a built in V reg, right ?

 

Yes. See below for wiring.
Redirect Notice

 

3g was wired in correctly and I got no power had to bring it to a second parts store and it checked bad. Hooked up the old voltage regulator and alternator it started, pull neg cable and it quit so I drove up to the parts store had it checked out no output.

Bought a new alternator had to put it in the truck because they did not have the plug and it show low output of around 12 volts. I keeped that one on since it show it had some output and they ordered a new one. When I got home pulled neg cable quits.

Thing is the gas gauge quit working when I started to have alternator problems. I know alt. was good before because I had it checked when I replace the ignition pigtail. Had an eletrical problem about a month ago intermittent power loss turned out pigtail was bad. I checked evrything at that time from bat. to alternator.

Just put new headers dual exhuast with mufflers all the way back. When I had other problem I put in new plugs, wires, rotor, pretronixs ignition. Don't see how this could cause problems.

Anyway i just got back from the junkyard and found a wiring harness from a 69 in fairly good shape. I going to pull mine loose from from the fuse box since there is a hack job from po. Hopefully I can fix hack job and solve problem. Still need a way to check alternator to see if it is good or not. If I can't do it from home I guess I will have to charge bat. and drive up to the parts store.

Is there a way to check for a short in the charging system?

Ok just check voltage with meter and I'm getting steady 12 volts but that colud be because of the low output alt.

 

Well, If you have everything wired correctly and everything is good, the original alternator and voltage regulator should cause a reading of about 13.8 volts across the battery terminals with the engine running (a little above idle,1200 to 1500 rpm). The 3G alternator should cause a reading of about 14.1 to 14.3 volts across the battery terminals under the same conditions. When you get to that point, your charging system will be working. You could still have other problems such as a bad battery or an accessory or wiring problem causing a current draw, but try to get the charging system working as described above, then we will look for other problems, if necessary.

 

The 3g is bad out of the picture for now. I got the harness partially out trying to fix a couple of bad wires I found. I'm going to fix them first the and see what happens. I stiil have to get the new alternator if it came in. The one in now reads 12 volts but like I said it had low output to begin with. I will let you know what happens.

 

I've seen a lot of alternators cooked from guys pulling batt. cables while the motor was running trying to switch batteries. Guys forget a alternator does not make voltage with out voltage going in to it. Not like the old generatorsd did. Hell you could run all day with a battery installed as long as you did not shut off the key. So you could be damaging it while trying to check it.
orich

 

Yea I was thinking about that after reading above. The reman.s they have now days are not very good. I was thinking maybe I fryed the 1g just because the battery was low. I'm also thinking maybe I did some damage to the 3g when I clocked it. I'm going to take it apart tomorrow see if maybe a loose connection or something. Find it hard to believe both alternator and the regulator are bad.

Took harness apart from the firewall back found a couple of wires that needed repair but where for brake warning light in dash and inst. cluster. Nothing that should affect the a;ternator. Guess I will find out tomorrow when I get it back together. Still have to check the wires in the engine compartment. Hopefully The new alternator will come in tomorrow and everything will be good.