Where to measure to make sure voltage regulator isn’t killing batteries?

[ComatoseLlama]

Hello

I’ve been having some electrical issues and narrowed it down to the voltage regulator. I think everything is fixed, but I already had to warranty my batteries once from this issue and want to make sure I won’t end up with another $200 battery bill.

I’ve got all the tools I’m just not sure where I should be measuring to make sure the voltage regulator isn’t going to kill my truck when it’s turned off.

Thanks
CL

 

[CDX825]

The regulator shouldn't kill the batteries when the truck is off. What kills the batteries more commonly is diodes in the alternator itself failing causing power to back feed when the truck isn't running.

An easy test would be to remove the wire from the B+ terminal on the alternator and hook a test light up between it and the alternator. With the truck off the light should not light. If it does light up you have a failed rectifier diode.

 

[Big Bart]

Some things to try.


First turn off the truck and pull the key. Shut everything off (GPS, cell phone charger, etc.) and close the door. (Dome lights need to be off.) Open the hood, if you have a hood light pull the bulb.

a) Pull the positive battery cable off on the driver’s side battery. Pull the positive battery cable on the passenger side battery. Hook up a test light between the positive battery terminal and the positive battery cable on the passenger side. You should see no light or a dim light if you have little to no draw. If you see a bright light you have a good size parasitic drain issue.

b) As long as the test light was dim or dark you should be good to go. (At least for a couple of weeks at a time.) If you want to test further you can hook up your test meter between the positive battery post and battery cable on the passenger side. Use the amp meter function on your meter (You usually also must move the lead to the 3rd hole on your meter for this feature.) You want to see something in the ranger of .5amp or less.

c) If your test light was bright or you amp meter suggested something more than .5 amps you should

i) Put the test light back on and unplug the regulator to see if the light goes out. (Bad regulator or wiring.)

ii) Then unplug everything on the alternator to see if the light goes out. (Bad alternator or wiring.)

iii) If the test light is still lit start pulling fuses till the light goes out. When the light goes out you know what part of the wiring harness is plugged into the offending device.


With that said it gets tricky with things like aftermarket stereos, aftermarket GPS's, aftermarket alarms, etc. So you may see that the fuse for the wipers is stopping the draw, but unknown to your the prior owner hooked a aftermarket alarm that is now malfunctioning. So check to see if you or a prior owner hooked something to the power feed off the offending fuse.

Let us know what the results are!

 

[Black dawg]

I have seen quite a few of these old external regulators cause a draw. They were warm to the touch when everything else was cold.

 

[dan-o]

I had to replace my batteries, too. Luckily, COSTCO didn't ask any questions. I have a parasitic draw, somewhere, and I don't run the truck much. It's a camper now.
To solve the issue I installed a couple of blade type battery switches on both negative terminals. It's an extra step, and probably wouldn't be needed if I drove it more.
Cheaper than replacing batteries.

 

[tradergem]

Your truck info doesn't say if it has a auto trans or not, however if it is a E40D check the transmission power relay which is located on my truck near the cruse control on the driver side. On my 90 the relay is directly wired to the constant hot side of the passenger side fender relay. They sometimes will stick in the on position which will draw power from the batteries even when the key in off. And they are not fused in any way.

I found this after all the above suggested checks looking for a parasitic draw failed. So I started looking at all the things that are directly fed power from the batteries. Good luck, finding parasitic draws are a royal pain to deal with.

 

[dan-o]

Your truck info doesn't say if it has a auto trans or not, however if it is a E40D check the transmission power relay which is located on my truck near the cruse control on the driver side. On my 90 the relay is directly wired to the constant hot side of the passenger side fender relay. They sometimes will stick in the on position which will draw power from the batteries even when the key in off. And they are not fused in any way.

I found this after all the above suggested checks looking for a parasitic draw failed. So I started looking at all the things that are directly fed power from the batteries. Good luck, finding parasitic draws are a royal pain to deal with.

Hmmmm...I wonder if that E4OD power relay could be a common denominator in my rigs' intermittent problem of the tach reading zero causing the tranny not to work AND, be the cause of the parasitic draw on my batteries.
If that relay is bad could it cause my tach to not work? Is that relay available?
I would be stoked, tradergem, if this is it!

 

[tradergem]

I found the replacement relay at advanced auto parts. I think it is standard motor part # RY-71. Parts Geek and Rockauto list them. The relay provides power to the TECA that controls the transmission.