14.2 sounds like what it should be! Did you check the starter cables/connections? Maybe that’s where you’re losing juice?? Assuming the alt/starter/fuse box/battery wiring configuration is same as my 95.
‘94 RRC LWB battery light
- Thread starter Blueboy
- Start date
Don’t those old things have different size alternator pulleys? What does the voltage do just off idle?
Yes. Used the pulley from the old alternator.
What is happening now is 14.2 at alternator and then it drops to 12.2 at the battery terminal from the alternator cable at idle. After driving 120 miles the battery showed 12.2 volts. Had the wipers and headlights on.
Yes feel the same on the 14.2 at alternator. Have not checked any other connections as yet. Seems like something is drawing power to prevent the battery from charging. Could be time just to take it to the shop.
If your saying that the field terminal on the back of the alternator is at 14.2v and the battery post is at 12.2 volts then that cable is loosing 2 volts. Do this..Measure the voltage drop in the positive cable the same way I told you to measure the voltage drop in the ground side.
Thanks. And yes that is exactly what is happening. Charging the battery now to get it back.
Ok, just did the measurements. Rover has been in garage and now dry.
NEG SIDE
Engine block - 0.01 v
Alternator case - 0.06 v
Body - 0.01 v
POS SIDE
Engine block - 13.2 v
Alternator - 13.2 v
Body - 13.2 v
And very interesting alternator cable at positive battery terminal 13.2 v!!!
Battery only charged to 13.1 volts to perform test. Normally fully charged is 13.8 - 15.0 v
Thoughts???
Thx
Engine was running. However forgot to load it up. Brain fart.
Will try again when the weather cooperates.
Thx
Well, if it’s like my 95, your big alternator cable runs to the fuse box. The two pos battery cables should go from the battery to the engine fuse box and starter. I would check pos and ground connections on starter and fuse box. Starter may be the culprit.
I will look again yet looks like alternator cable goes directly to the battery. It is not a very robust cable either. However everything is wrapped in plastic so hard to tell. It is brown and looks the same at the alternator and positive battery post. There are 2 other cables that attach to the positive terminal. One is the fuseable link and the other is power for the speaker system. Also my winch cable is attached. The starter cable is lugged into the positive terminal. Chasing electrons has never been my forte!
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If you have the fuse box shown below, the smaller less robust brown wire I highlighted runs from the alternator to the fuse box. Then another brown wire runs from the fuse box to the battery. So the fuse box has the 100A fuse between the two.. Do those connections look ok?
The second battery connection is a normal size cable, directly to the starter. From underneath, see if the pos & neg connections on the starter are clean and good.
BUT…. maybe someone with a 94 can comment what their layout is. I just don’t know if 94 & my 95 are different.
Yea, electrical work sux! But cleaning connections is easy. We’re just looking for what’s restricting the voltage after it leaves the alternator.
If you had a constant draw that big, like from the winch, your battery would be dead p quick when it’s parked for a week or two. You can unplug the speaker power since it’s probably only draws power when truck is running (ignition is on)
The second battery connection is a normal size cable, directly to the starter. From underneath, see if the pos & neg connections on the starter are clean and good.
BUT…. maybe someone with a 94 can comment what their layout is. I just don’t know if 94 & my 95 are different.
Yea, electrical work sux! But cleaning connections is easy. We’re just looking for what’s restricting the voltage after it leaves the alternator.
If you had a constant draw that big, like from the winch, your battery would be dead p quick when it’s parked for a week or two. You can unplug the speaker power since it’s probably only draws power when truck is running (ignition is on)
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Looked at my buddy’s 94 tonight which is definitely different than a 95. He gave me a couple very easy tests from the manual to see if it’s a power cable issue or ground issue.
Which ever of these shows your significant voltage drop, that should tell us where to look. First test is the power side and second test is the ground side.
Which ever of these shows your significant voltage drop, that should tell us where to look. First test is the power side and second test is the ground side.
Yes, kinda thought the ‘94 was different from ‘95. Actually have the workshop manual and will look up that section.
edit: Found it!
Also Discostew has given some ideas on checking for voltage drop.
Thanks.
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Thats all good information. When the engine is running true ground is the alternator case and true battery pos. is the field terminal. When the engine is running the battery is just along for the ride.
Exactly.!
My guess is, you will see the voltage drop on the second test which is alternator power to battery negative terminal. That would mean you have a ground issue. Even loose alternator bolts can mess up the ground. Something to check if ground is your problem.
On the back of the alternator are 3 posts.
1 is brown wire which I am assuming goes to battery
2 not sure
3 assuming is the lead to the tach
is the center post the + post the manual references??
None of them are marked.
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Please see post to Discostew.
Need reference on generator + terminal location.
Better pic of connections.
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