Hi All, New member, first time poster. More questions and post to come I'm sure. I have a 63' C10 Longed 283, 4 speed. Fairly unmolested and just acquired. Trying to work through some issues. Here's what is going on. Will need to jump to start if sits 3+ days. Fires right up in between. Will "surge" while cruising at highway speeds, lost power for a fraction of a second on highway yesterday. Voltage gauge in dash cluster will dance around a bit and will be pegged to high as well. With the truck off and sitting overnight, the voltage at the battery is 12. New battery 3 months ago. With truck running at idle voltage at battery varies from 12.7 to 13.5 ( no accessories on). Voltage at alternator at idle varies constantly from 13.9 to 14.6. At RPM the alternator voltage again jumps around from 14.9 to 15.4. So I know that the voltage should not be jumping around like this. I'm thinking this is likely the cause of the surging as well? Is there a way to tell if this is an alternator problem v a voltage regulator issue. Replace one or both or scrap both and convert to internally regulated alternator? Any thoughts appreciated. Thanks!
Make sure grounds, cables, and all electrical connections to block, frame, and firewall are fresh and clean and bright, and tightened securely. The voltage regulator itself has to "see" the same ground potential as everything else or it will get confused. Loose, missing, or corroded grounds cause big problems even when things seem to be working.
One diode in the alt. is toast. If you had idiot lights instead of gauges, the charge light would be glowing dimly.
Hi guys, Thanks for the advice. I went ahead and cleaned the grounds from the valve cover to the firewall and firewall to block. Replaced negative battery cable as well. I didn't see anything else terribly worrisome. Nothing under the hood is clean and bright but they are secure. After cleaning grounds and replacing negative battery cable the voltage at the alternator when idling is between 14.5 and 15. At RPM it is staying around 15 to 15.2, but not jumping around as much as prior. This is still causing the gauge in the cab to be pegged to the right still. So just double checking that it is time to move on to the alternator? Recommendations on which one to get. I see an internally regulated 100amp model from LMC Truck with a wiring harness conversion. Worth the $170? I'm not necessarily planning on adding a whole bunch of electrical to the truck so maybe stick with externally regulated 63amp? Thoughts appreciated. Thanks all! Jon
I've been running the external regulated (1960s style) alternator in my Chevy II for 5 years, seems to be doing fine....and they're cheap and don't require any wiring changes. The regulator might be acting up, the alternator might have a problem, but figuring out which is the problem can be challenging. Do you have a battery charger, so you can fully charge the battery, then see how it does? that might drop the voltage down, and also get the ammeter back towards the center. To check for a bad diode, maybe you could measure if there's a current draw, when the truck is turned off. First see if there's a slight spark when you connect/disconnect the battery negative terminal. If you don't see one, then you can also check further by connecting a light bulb between the battery and cable, and if it lights up, that means there's something drawing current when it's not supposed to be. What I'm thinking is that there is a drain that is making the battery need to be recharged a lot as you're driving, which is making the ammeter show C, and causing the voltage to be high.
@302GMC called it I think, the altenator probably has a bad diode, they have 6, I think. So it's maybe shorted, and that's why battery is draining after a day or two? Rebuilding an alternator is pretty easy, and then you know what you have. New bearings, diode pack, voltage regulator etc. inexpensive too.
Thanks everyone for your thoughts. Drove the truck to work this morning after charging battery from the alternator yesterday and disconnecting overnight. 12.4 volts at battery. No abnormalities noted this morning on the drive in. Gauge was stable. So maybe there is a drain somewhere. I will check for spark from the battery neg cable when disconnecting (no light bulb). May have to check for drain with multimeter too. Will see if acts up tonight. Thanks again, will keep you posted. Jon P
If your voltage is vastly changing, I would think it is a bad connection somewhere. Most likely on the charge or 'sense' wire. Check the connections to the VR, pull the tab off and look at all the connectors going to the VR, they should be clean and tight. Check the terminals on the VR, they should also be clean. Check the wire harness from the VR to the ALT. Look for any corroded, loose, or frayed wires at the terminals. VR side is usually .250" female spade, and there is usually enough wire to cut off the old terminal and crimp a new one on. You can pull the old terminals out of the plastic tab by sliding a pick down the front side of the connector to release the terminal. ALT side of the harness gets beat up a bit from people working on the engine. Verify all connections are clean and tight with no frayed or damaged connectors to the alt. Verify the VRs is properly bolted down and grounding to the body. If it is still held on with sheetmetal screws/bolts I replace them with 1/4-28 bolts and nylocks. Sand down the feet of the VR and the body where it will contact, then add some OX-Guard and lock it down. If there was ever any repair work or added electrical do-dads done to the truck, check that the wiring between the ALT and VR was not spliced into or intercepted. I've found a few vehicles where someone needed a switched source and they tap into the VR harness. Depending on what leg they tapped into, this can screw up the charge 'sense' wire and the VR may buck/boost the voltage incorrectly. GMs VR/ALT system is solid. Don't bother with the 1 or 3 wire alternators unless you are in desperate need of something more than 60A. Then skip the 10SI an go for a 12SI unit. If you are good with a voltmeter check out http://www.madelectrical.com/electrical-tech.shtml
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