Hey guys,

Background: 87'GXL with new Alt and new battery put in 2 months ago.

Tonight while driving I noticed the Battery gauge in the dash would drop from just below 14 V to just below 13V whenever I applied brakes to stop at a light or so. I also noticed the dash light would dim a bit at this time aswell.

I've searched, didn't find to much with my search terms.

Any ideas?

Thanks,

Mark

 

S4 alt is not putting out enough charge. I swapped in an FD, and that went away.

 

The S4 Alt was designed by mazda for a reason.. so unless you're running some crazy stereo with a huge amp.. i dont see why it wouldn't put out more than enough charge.. especially if it's brand new.

and the FD alt swap isn't just a bolt on swap.. it actually requires a little bit of work.

But as for your problem.. I don't really know what to tell ya, im no guru.

 

what you might want to consider is to redo all the power and ground wires under your hood. if that doesnt help then you can find a local shop that can rebuild your alt and beef it up for you. other then that you should be fine unless you are running a crazy stereo system with a big amp. then do the conversion to fd and yes it is a bit of work.

Brian

 

Interesting
I have the same problem. It really hasn’t effected anything, I figured there was some sort of short in the wiring some where. It is quite a substantial voltage drop for just the brake lights.
My car has done this ever since I bought it 2 years ago. I will get around to tracing it down some day

new batts and alternators did not fix it

 

I definately have no crazy stereo/amp running. I don't even have a cd player hooked up.

I'll check out all the wires and grounds though.

 

voltage should and will drop whne the brakes are on cause of the brake lights, i dont know about a full volt, but it will drop, also if the lights inside dim, if they dim alot something else is up, if its just a tiny bit dimmer, its due to the normal voltage drop and dont worry, a bigger alt will help, like the FD from what i have heard but you shouldnt have any problems the way it is unless something else is going on

 

I have that kind of an issue and I swaped to an fd alt and it went away (That was before I had my sound system in). If you have a big stereo the FD alt is not the best idea because it won't put out enough power for the bigger systems. Also it's a good idea to redo the grounds because it is a 19+ year old car.

 

Try figuring out how much current is going through all those stop lamps?
Hint, it's close to 10A.

How much amperes you think the stock alternator is putting out at idle?
Yeah, not enough.


-Ted

 

I have a small drop, but nothing to major.....yet. I expect it out of a car as old as mine. I will be redoing most of the wiring soon though so I expect it to go away considering I have a pretty stock sound system.

 

I had this same issue. I just put in some new ground wires yesterday and while there's still a drop it's not nearly as bad. I added a ground from the Bat (-) to the drivers side strut tower, from bat (-) to the block where it originally grounded to the firewall, and replaced the original ground to the firewall by the wiper motor. I used 4 gauge wire for all of these. I'm also planning to ground the alt and the starter and run new (+) leads to them but have not gotten to that yet.

 

My car does this too. My dash lights just get a hair dimmer and I've got a big sound system and everything. (Stock S4 Alt.)

EDIT: I just realized I resurrected an old thread . . . oopsie. Oh well, maybe it'll be helpful for someone to read. :-P

Cheers,
Cody