Diodes in Alternator regulator seem to be gone - parasitic drain

[thelal]

Been chasing a heavy parasitic drain on my main battery for quite some time
Pulled all fuses & relays and tried multimeter in series (fuse checking & circuit) etc. with no luck

Pulled main heavy cable from battery (v-post) to alternator and 4 prong electrical connector. Left for 3 days and held battery 12.8v without dropping. Up to this point it (with ALT connected) it would pull to 10.5-11.5v

With truck running I get an AC reading of 31v across POS & NEG terminals on battery which implies diodes gone (per some other posts)

Are the diodes on the regulator replaceable or best to just replace the regulator?
Any issue with ebay versions compared to OEM ($115 via Amayama/Partsouq)

I've replaced the brushes on the alternator but no other maintaince on it. Truck at 360K - 97 1fzfe
Thanks

 

[thelal]

methinks its the "Rectifier" (which contains the diodes) and not the regulator that needs replacing?

 

[thelal]

Is the 27357-55080 right part number?

methinks its the "Rectifier" (which contains the diodes) and not the regulator that needs replacing?

@george_tlc what you think?

 

[george_tlc]

Likely dead/shorted rectifier diode(s). The FSM shows how to measure/test each diode for open/short, but you will need to remove and open up the alternator to pull the diode stack assembly out. At that point may as well replace the assembly.

Of course while it's apart you would want to check the bearings etc. Replacing with a reman or new may be a better alternative...

cheers,
george.

 

[jonheld]

It's less expensive to replace the entire alternator than to replace the rectifier board.

 

[thelal]

cheers

 

[thelal]

just replaced with a new (Chinese) alternator. No difference. Still drops 12.7v->9v overnight
Will recharge and start pulling the AMx fuses (fusible link) to see what circuit is pulling the amps

 

[use2bn83]

just replaced with a new (Chinese) alternator. No difference. Still drops 12.7v->9v overnight
Will recharge and start pulling the AMx fuses (fusible link) to see what circuit is pulling the amps

While a shot in the dark, and not meant to derail proper diagnosis, but my factory speaker amplifier on the right side of the glove box had a huge parasitic draw that was nearly as bad as yours. It was already not being used due to an aftermarket stereo install, so I just unplugged it and the draw went away.

I just started probing fuse locations on (Key off) 10a mode and eventually found a circuit that was pulling almost an amp if I recall. I don’t recall the fuse, but a Quick Look in the FSM would show it.

Edit: Looks like it was the 10a dome light fuse. And a US spec fzj80

 

[tmxmotorsports]

While a shot in the dark, and not meant to derail proper diagnosis, but my factory speaker amplifier on the right side of the glove box had a huge parasitic draw that was nearly as bad as yours. It was already not being used due to an aftermarket stereo install, so I just unplugged it and the draw went away.

I just started probing fuse locations on (Key off) 10a mode and eventually found a circuit that was pulling almost an amp if I recall. I don’t recall the fuse, but a Quick Look in the FSM would show it.

Edit: Looks like it was the 10a dome light fuse. And a US spec fzj80

This was the culprit of my problems

 

[thelal]

thanks will take a look

 

[Kernal]

@thelal : maybe check also that the brake lights aren't on while the vehicle is parked??
There's a small round plastic cushion that the brake lamp switch presses on that can fracture and then fall out. When that happens the brake lights can come on while the vehicle is parked. Check also that the brake pedal return spring is still connected.

Red arrow pointing to black plastic brake switch cushion.
Immediately above that is the brake pedal return spring
(photo taken from the driver's foot-well looking upward, firewall to the left, steering shaft to the right)

 

[azusa]

Does your volt meter have a amp setting? Haven't seen one myself, seems like dealerships are using infrared to find the parasite. Take the alternator belt off and have the alternator connected, if the alternator is energized, turning the pulley would be really hard. also you can feel the temperature difference on the alternator housing.

 

[thelal]

@thelal : maybe check also that the brake lights aren't on while the vehicle is parked??
There's a small round plastic cushion that the brake lamp switch presses on that can fracture and then fall out. When that happens the brake lights can come on while the vehicle is parked. Check also that the brake pedal return spring is still connected.
..

Hadn't thought of that. Will check