Alternator...Battery Light...Brake Light WTF!

[jdub]

Ok...here's what I did:

1) Alternator went bad...showed 11.5 volts on the dash meter; plus it was very hot to the touch
2) Replaced battery w/ brand new one 850 amp

I bought a MR2 alternator '91 (w/ powersteering)...thought I'd upgrade to a 100 amp one since the old alternator was bad. During the install, all 3 wires on the connector were very brittle and two broke off even with the plug. I bought another plug and spliced the wires...the splices are good. I used my old alternator pulley to match the belt...fit perfectly. The MR2 alternator fit fine...a little tight, but no real issues. Belt is nice and tight too

Got everything back together and now the dash battery light and brake light come on very dim. The volt meter shows 13-14 volts depending on rpm. Also, the headlights and interior lights are dimmer at idle...over 1000 rpm, lights are normal. The battery and brake light stay on regardless of rpm.

I had the new MR2 alternator tested before I left the parts store. I also had it tested on the car...that's how I found out my previous 3 year old battery was going bad. The new alternator tested within spec on both the bench and on car tester.

I've checked wiring...I can't figure this one out. Why would my battery & brake light come on like this? I know it usually means the alternator is going bad, but the volts read w/in spec. Any ideas?

Thanks

 

[tubbie]

My LS400 had that same problem a while back. All those same lights were always on, and it was charging 13-14 volts. I replaced it with a new one from the parts store, same problem. Took that one back and exchanged it for another one again and problem resolved.

It has to do with the internal circuitry on the voltage regulator. Alternator may be working fine, but the coltage regulator could be failing, that's why you get all the lights.

 

[boost fiend]

you can buy a new part and go home to find that its not working like it should. thats why they come with warrenty's. or start checking cable connections and grounds. power has to go somewhere.

 

[jdub]

Yeah...been there. Went through 3 "brand new" alternators on my son's truck before we got one that worked right.

I did check the grounds...I've got additional grounding straps going to the block on both sides and a new grounding wire going to the battery.

I guess I was hoping you guys might know something I missed...but, I think Tubbie is right. A friggin bad voltage regulator!

 

[tropical 87t]

I had the same problem with the battery and brake lights on. I went through 2 alternators before they went away with the 3rd one. Mine were bad voltage regulators.

 

[jdub]

Aggghhh...wouldn't it be nice to be able to go to the parts store and buy an alternator that WORKED. You spend the time fixing your car and install a "NEW" part that doesn't friggin work...then you get to re-do it all over again.

Well...done venting...thanks for the help guys!

 

[aye mate]

I have the same problem with my batt. and brake light staying on. I have a new alternator and the car runs fine but these lights are on all the time.

 

[wardog]

What Year Of Mr2 Turbo/na Does The Alternator Swap With The Mk3? THE MK3 IS 80 AMP AND THE MRS IS 100AMPS? Direct Bolt On Or Whats The Deal, Mine Has A Loud Squeaking Noise And When Use My Blinker All The Dash Lights Blink Too Any Ideas What This Might Be IT Has A New Battery..

 

[jdub]

Ok...here's what I did:

1) Alternator went bad...showed 11.5 volts on the dash meter; plus it was very hot to the touch
2) Replaced battery w/ brand new one 850 amp

I bought a MR2 alternator '91 (w/ powersteering)...thought I'd upgrade to a 100 amp one since the old alternator was bad. During the install, all 3 wires on the connector were very brittle and two broke off even with the plug. I bought another plug and spliced the wires...the splices are good. I used my old alternator pulley to match the belt...fit perfectly. The MR2 alternator fit fine...a little tight, but no real issues. Belt is nice and tight too

Got everything back together and now the dash battery light and brake light come on very dim. The volt meter shows 13-14 volts depending on rpm. Also, the headlights and interior lights are dimmer at idle...over 1000 rpm, lights are normal. The battery and brake light stay on regardless of rpm.

I had the new MR2 alternator tested before I left the parts store. I also had it tested on the car...that's how I found out my previous 3 year old battery was going bad. The new alternator tested within spec on both the bench and on car tester.

I've checked wiring...I can't figure this one out. Why would my battery & brake light come on like this? I know it usually means the alternator is going bad, but the volts read w/in spec. Any ideas?

Thanks

Ok...revive the thread...I just changed the alternator (again) and I still have the dash brake and battery lights. Very dim...this is driving me nuts! I tested the battery...good (12.5 volts). Cranked the car, voltage went up to 14.4 volts. Is there a fuse or some relay that runs these lights? I'm starting to think this is not the alternator...any MK III electrical gurus out there?

Thanks