• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

'94 B4000 Battery Light On


Steve777

New Member
Joined
Dec 23, 2017
Messages
16
Reaction score
0
Points
1
Location
Colorado
Vehicle Year
1994
Make / Model
mazda
Engine Size
4.0l
Transmission
Manual
Noticed the battery light on while driving today; made it home OK and then started checking the battery voltage. About 12v with the engine off; drop to 11.7v or so at idle and does not get any better if the engine is rev's up. Battery charges up just fine on an AC charger (which I am doing now).

So normally I'd assume its the alternator, but before I rush out to buy a new one I thought I should check the fusible links (which I assume this car has). I don't have a wiring diagram, but I would guess there are two links, a big one on the main power line and a smaller one on the voltage sensing line to the alt. I was looking for an easy way to test if these are good without digging around the wiring harnesses, and had a couple of thoughts:

On the big one, I would assume if there is batt voltage at the big terminal on the alt then its fusible link is good. Same with the sensing wire, but probably have to have the ign on and maybe the engine running to see voltage there.

Does this plan sound right? Any other ideas? Or does someone know where these fusible links are?

TIA
 


RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,123
Reaction score
8,204
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Key OFF
The B+ wire on alternator, stud/nut terminal, should have battery volts, if fuses are OK

Unplug the 3 wire connector on alternator
Yellow wire should have Battery volts if fuses are OK

Green wire 0 volts
Turn on key
Green wire should now have battery volts, just slightly less is OK, because key is on now, this is Battery Light wire, just FYI

Make sure short white jumper wire is plugged into alternator

If these 3 wires test OK, and engine running battery volts are less than 13.5volts then replace alternator
 

Steve777

New Member
Joined
Dec 23, 2017
Messages
16
Reaction score
0
Points
1
Location
Colorado
Vehicle Year
1994
Make / Model
mazda
Engine Size
4.0l
Transmission
Manual
Thanks RonD!

Yellow and green wires work as you say they should. So likely fusible links are fine. Not sure what you mean by the "short white jumper wire". There is a white and black wire in the center position between the yellow and green. And there is white and black wire in a separate connector further down, that I see. Did you mean one of these, or is there another white wire supposed to be there, somewhere?

Unless there is a missing white wire somewhere else, I think I've convinced myself that the fusible links are good, so it is most likely new alt time...
 

RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,123
Reaction score
8,204
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
It is the same wire, white/black, just a jumper wire that connects Voltage regulator(3 wire connector) to the Stator inside alternator, single spade terminal
 

Steve777

New Member
Joined
Dec 23, 2017
Messages
16
Reaction score
0
Points
1
Location
Colorado
Vehicle Year
1994
Make / Model
mazda
Engine Size
4.0l
Transmission
Manual
OK. New alternator it is. Thanks again.
 
Last edited:

Sponsored Ad


Sponsored Ad

Staff online

Today's birthdays

Member & Vendor Upgrades

For a small yearly donation, you can support this forum and receive a 'Supporting Member' banner, or become a 'Supporting Vendor' and promote your products here. Click the banner to find out how.

Truck of The Month


Yotaismygame
February Truck of The Month

Recently Featured

Want to see your truck here? Share your photos and details in the forum.

Follow TRS On Instagram

TRS Events

Check Out The TRS Store


Sponsored Ad


Sponsored Ad

Sponsored Ad


Amazon Deals

Top