Charging issue

[84prspctr]

I’m having charging issues. Brand new wiring harness. I made sure every terminal is shiny. Old 12si alternator was making whining noises and was dropping down to 12.4 volts with headlights and bumper lights on. I replaced it with a new 100 amp 10si style alternator. Now it’s getting down to 11.9 volts with the lights and bumper lights on. I tested voltage at the battery and at the alternator and it’s all the same. When I start the truck it is at 14.5 with no lights on. After driving the truck with no lights on and the radio on it’s at 13.3. What should I do next. The battery cranks the truck good and fast. I need the truck charging good and reliably as soon as possible as I have a cruise parade it’s entered in this Friday and need my lights on for it.

 

[84prspctr]

Here’s an update, the new alternator isn’t charging at all anymore. I confirmed this by unplugging the connector from the alternator while it’s running and it’s staying at 12.92 plugged in or not. Doesn’t matter if I rev it or anything now, not charging. Tomorrow I will put my old 12si alternator on there and see if it will charge.

 

[SirRobyn0]

Here’s an update, the new alternator isn’t charging at all anymore. I confirmed this by unplugging the connector from the alternator while it’s running and it’s staying at 12.92 plugged in or not. Doesn’t matter if I rev it or anything now, not charging. Tomorrow I will put my old 12si alternator on there and see if it will charge.

I was going to say, bad ground or bad alternator, certainly installing your old unit will be a good test.

 

[84prspctr]

I cleaned every ground, there’s one going from the battery to the rad support, one going from the battery to the engine block, and one going from the battery to the alternator top bracket. The old alternator would charge it ok with no lights on, and up to 12.7-13.4 volts with the headlights on. But once I would turn those bumper off road lights on and hit the brakes the voltage would drop to 12.3 eventually at idle and it would sound like a supercharger revving.

 

[PrairieDrifter]

Sounds like a tired old alt and a bad new one.

 

[84prspctr]

The new one worked for about 10 minutes. Quality has really gone down hill I guess. Where would you recommend buying an alternator from?

 

[SirRobyn0]

The new one worked for about 10 minutes. Quality has really gone down hill I guess. Where would you recommend buying an alternator from?

I would recommend purchasing a new alternator and staying away from remanufactured. Denso or A/C Delco are always my first choice. I try to steer clear of parts store "house" brands because those are just names and it can be hard to tell who made it. With that said we have had good luck with Masterpro which is Orielly's house brand. But definitely A/C Delco and Denso first in line. BTW O'reilly's has the ability to order directly from A/C Delco, you just have to find someone at the store that knows how to do it.

 

[PrairieDrifter]

Agreed^ or Remy, that was going to be my choice. I had my alt last about 6 years, but i definitely abused it while building my truck and the first few years with all the tuning and what not. Can't remember the brand though, but it started only putting out 13 volts and started getting hot and whiney lol

Im upgrading to a Mechman for all my extra lights and sound system. I was going to try a 94 amp remy, but decided to finally install that Mechman I've had for awhile now. Just didn't have one last piece, have 2/0 cable going in.

 

[Scott91370]

If you have a place in town (they're getting harder to find) that canrebuild your alternator thta would be the best bet.

 

[Snoots]

A 10SI will never have the output of a 12SI. Got to an AD230 or AD244.
When you said you unplugged your alt the voltage stayed the same, that's because you took away the actuator wire. There was nothing there to turn the alt on.

 

[84prspctr]

It doesn’t matter if I have the trigger wire plugged in or not, it won’t charge. This one was a brand new one from db electrical. I’m going to have my old alternator tested, I measured the resistance in the battery wire going to the alternator and it’s 0.01 ohms.

 

[SirRobyn0]

If you have a place in town (they're getting harder to find) that canrebuild your alternator thta would be the best bet.

Agreed. There use to be a really great guy in the area, but he is now long gone.....

 

[84prspctr]

going to get the alternator and battery tested right now. I won’t be able to get a new delco remy unit by Friday, oreilly has a Wilson 12si 94amp reman alternator and a ultima reman alternator that would be here by tomorrow morning. The Wilson has a 1 year warranty and is 75 dollars, while the ultima is 104 and has a lifetime warranty. I’ve had issues with ultima in the past, but they have that lifetime warranty. Would the Wilson be a better choice?

 

[84prspctr]

Second new alternator is on, we’re charging a little better. 14.5 on startup, 13.8 at hot 500 rpm idle, when I turn the lights on it goes down to 13.2 at idle and comes up to 13.5 or so at 2K rpm. When I turn my bumper lights on it drops down below 13 still at idle. This one is a 94 amp 12si

 

[PrairieDrifter]

What size are your battery and charge wires?