amp gauge flickering, lights too!

[71/454]

Hey guys,
My 72 has the amp gauge flickering really hard to the charge side intermittently. I thought it was the gauge till I drove it and the headlights flicker dim to bright. Meter on battery says 12.17 at idle (seems low), hits 13.30 if I rev it. If I meter the output stud on the alt it says 12.82. Oh and it doesn't seem to act up at idle, just while driving, somewhere around 1500-2000 it seems to start. It has an internally regulated alt swap and previously worked fine. My first guess was the alt was going out but I changed the engine this winter and I think this has been going on since then.

[WIDESIDE72]

Check to be sure all of your ground connections are 1. intact 2.clean and 3. tight. I had a recent situation recently.

[71/454]

I did take off the ground from the battery to the block and it seemed fine. The only other grounds I think that are there would be the battery to body and the ground strap off the old voltage regulator on the drivers side. I'll check those I guess. Any more ideas? Or are there any more grounds that are missing. I'm really not an electrical guy

[smn69]

Other ground locations are, (others could correct me on this) Firewall to engine, bottom of cab (passenger side) to frame, Bed to frame (drivers side in the back), and passenger inner fender to frame. Good clean connections can make a big difference.

[Classic Heartbeat]

How many amps is your alternator? 45 amp alternators will do that at idle when they get old. I would use at least a 75 amp alternator. WES

[71/454]

Thanks guys. I'll try some of those locations. The more I think of it I had to move the horn for some of my turbo stuff and I bolted it back down using the ground bolt for the regulator, I am thinking beacause it is new this year that must be it. although I don't think I have a firewall to engine ground maybe I'll make one.
Wes I'm not sure the amps on the alt. It is a newer looking one and it has been converted to internal regulator so I'm guessing it's at least 60

[68gmsee]

Originally Posted by 71/454

......... although I don't think I have a firewall to engine ground maybe I'll make one.......

One thing I found out last year is that grounding problems can cause some weird problems that just don't make sense.

Here's what I grounded with "new" cables and haven't had any problems since:

1.New ground cable from battery to the engine and one from there to the frame. (I didn't trust the cab ground or radiator support ground since the bolts are old.)
2. Ground cable from cab to the frame.
3. Bed to the frame.
4. Battery to the radiator support.

Overkill is better than not enough.

[C20-67_N_MO]

If it's not too much problems I would take the Alternator to a local parts store and have them check it out. If thats not the problem then the battery might be going bad.

Just a thought.

[71/454]

And the rookie of the year goes to.... me for missing the basics
I took the remounted horn off where the other grounds are screwed too and it had a nice layer of black paint on both sides I had to use a grinder to get off. You would have think I would have noticed that when I put it together. I also checked the tension on the belt, not loose but not tight either, so I tightened it too. Now the voltage is over 14 at idle. It still has the odd flicker and I haven't tried it at night yet with headlights but I think it's fixed. I am going to make some new ground cables and do it right though just to be sure, thanks for the help and suggestions guys

[71/454]

Ok digging this up again. I thought I fixed this and when I checked it was fine just after warming up. What I see now is that it only starts to flicker after the truck has been warmed up and run down the road a bit. This to me is telling me the voltage regulator is failing after getting warm. What do you guys think?

[71/454]

Update. I changed the alt and sure enough it fixed it. Sometimes it's wise to not overlook the obvious