77 f250, i6 2wd. Converted to 3g alternator, newish relay, newish starter

Son is at college, so I have limited access to the truck, so I am trying to figure out what to troubleshoot before I go there again

the brake light switch that I replaced apparently didn’t engage fully and the tail light ran down the battery

Son called aaa and they tried a jump box and no luck. Then a diesel truck came by and got it going but had an issue where it ket trying to start even with key out of ignition. He got it running and then siding idle it high enough and died

I got there last night and volts, replaced the battery and 175amp fuse for alternator because the Volts show it’s not charging. It starts and idles fine now, no continuous starter run, just isn’t charging

messed with wiring and checking fuses until 11 and had to go home

so, what can I check when I go back? I’m wondering if either the relay is bad or the alternator is bad? Maybe blew out the diode? I cut out a inline wire fuse (old style) to make sure there wasn’t a signal problem.

I can yank the alternator and have Autozone test it, I bought it new from them. If bad, replace, but if not, maybe replace relay too while I’m there.

Other than those two things, I thought I may have to put in fresh wiring to eliminate old wire issues.

any suggestions are welcome.

 

Did you try revving the engine? Sometimes those 3Gs need some RPMs to kick them into charging.

 

he revved it up and followed normal process we used before that always worked. This alternator has been on for a year...low miles but no problems before

feels like a blown fuse type of issue, just not running

 

A normal 3G should not require revving to work. A converted "1-wire" like we sell definitely requires a quick rev to somewhere between 1100 and 1500 rpm initially, but once there is good all the way down to low idle until you turn the engine off.
The Green w/red exciter wire is there to eliminate that problem. Turns the alternator "on" until the key is turned to OFF again.

A couple of things to do with a volt/ohm meter.
1. Unplug the 3-wire connector from the side of the alternator and check the terminal with the Yellow w/white wire. Should see full battery voltage all the time. Key ON or OFF.
2. Next, with the key turned to ON (not ACC though) you should see pretty close to battery voltage on the Green w/red wire's terminal too.
3. Verify that the White w/black wire is correctly plugged into the separate spade terminal on the side of the alternator. Sometimes they look like they're connected but are just stuck in next to the connector.

What fuse did you bypass? The big 175a fuse in the main charge line? If so, that pretty much eliminates that as a problem area. But what about the cable itself? Any chance it's failing from some bad end crimp or something? Is it a store-bought cable, or home made?

Regarding the starter relay, there is literally NOTHING in the relay that can stop the battery from being charged. Your charge wire is in direct contact with the battery cable there on the relay's stud, so nothing else on the vehicle can be in the way of that connection. As long as the two cable's ends are touching each other, there's nothing else to check other than the cables themselves.
The fact that the engine cranks with the starter means that the battery cable is still good, so a cable fault would only be from between the alternator and starter relay.

Not sure what could have happened during the long cranking and the false cranking, but I would definitely take the time to go have the alternator checked. Yes it's a pain, but if all the other wires check out then the alternator would be the next culprit in line.
But definitely check for 12v at the Green w/red wire. Without it your alternator will never turn on.

Paul

 

Thanks for the suggestions, I forgot to check power from green/red wire. It that’s the online fuse I bypassed, didn’t bypass the 175fuse but put a new one in there. Cables are all newish from store.

I will test that wire and likely will have to yank the alternator which isn’t too bad, just a hassle

 

The green and red wire should have about 7-9 volts, the alt grounds it and it runs through the "ALT" bulb check it needs that resistance to operate. So power to "ALT" or "BATT" light from fused ign to cluster then out to alternator. with out this circuit it will not charge. I think a 194 bulb would work

 

So I went there tonight. Tested green/red wire and it had power (11. Something volts) so I yanked the alternator and got a new one. Worked right away.

Had to replace a fuse in the stereo, a light switch and the tach was messed up for a bit.

I think when that guy jumped it, he did something that fed backward and that’s what zapped the alternator and other things.