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· RIP E46, hello E39
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194 Posts
Discussion Starter · #1 ·
Hey all, i know this topic has been tossed around a whole lot but i havent been able to find an answer to the problem i am having so here we go, put the key in the ignition and turn it on, only the oil light comes on along with the si board, inspection light, all the guages work, just the lights do not as well as the odometer (which none do anymore). my alternator will charge over 3k rpm which is normal when the charging light bulb is burned out but ive replaced mine and bench tested the bulb and its fine. unhooked the blue wire from the alternator and grounded it which should of made the battery light come on but it doesnt. so heres my question is there any way to bypass the cluster so the alternator can charge the battery below 3k rpm so i can actually drive my car normally? thanks all
 

· livin large
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7,613 Posts
wait. stop. you do not need to bypass the cluster for your alternator to charge the battery. what you need to do is take a volt meter and check the battery before you start the engine, should be between 11.2-12.4. then start the engine. at idle, it should read between 13.2-14.8. if you have low reading when at idle, then the alternator isnt producing the power, and you need to change it.
 

· RIP E46, hello E39
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194 Posts
Discussion Starter · #3 ·
unfortunately i left my DMM at work, ill have to get back to you tomorrow on the readings, i thought i had solved the problem but turns out ive been running on the battery alone for that time oops
 

· RIP E46, hello E39
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194 Posts
Discussion Starter · #4 ·
old cluster: battery start 12.48 idle(no load) 12.21, 3k rpm 13.63v, idle w/ load 11.83v, 3k with load 13.18

new cluster: idle no load 13.68v, idle load 13.28, 3k rpm no load 13.66, 3k with load 13.28v

does this still seem low to you? i dont have much experience with older alternators but i thought it should have been closer to 14v. but i may be wrong
 

· livin large
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7,613 Posts
that is weird my friend. the cluster shouldnt have that effect on the voltage drop.

try driving around for 10 minutes with the old cluster and rechecking the volts at idle with no load. either something is shorting inside the cluster or maybe something is going on with the windings
 

· RIP E46, hello E39
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194 Posts
Discussion Starter · #6 ·
in the old cluster the battery light never came on when i turned the ignition on, the new cluster solved that problem and the alternator now charges at idle. now a new problem is that the alternator isnt putting out enough voltage. the belt isnt slipping so im suspecting that the voltage regulator is shot.
 

· Nick's Toys
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1,386 Posts
On a lot of older vehicles the light acts as a excitor for your Alternator.
13.6v is quite Ok for a Bosch alternator :)
The only way to see if your Alternator is charging enough is to load it with about 50 A (in SA these cars came with 60 & 80A alternators).
If you can check for frequency then make sure there are no ripples on the Battery !
Sometimes the diodes in the regulator go sporadically, sending 300v riples through your system :yikes:
 

· Registered
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466 Posts
I am going through diagnostics to correct an alternator that is "chirping" at me. I believe the bears are shot on it and It needs to be replaced.

I am trying to decide to have it rebuilt or to buy a new one.

here are my symptoms:
-my battery is completely dead. I have to jump it each time.(there is a drain somewhere)
- while i have the jumper cables attached the car runs very smoothly
- when i take my jumper cables off the car has a fluctuating idle, its not significant but i can notice it.

Thoughts?

I have not done the voltage readings while it is running yet, Which i will do this weekend.
 

· RIP E46, hello E39
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194 Posts
Discussion Starter · #10 ·
Well turns out my problem was the ground wire from the alternator to the back of the cluster had an open in it so I repaired that and now everything is fine. Put a new voltage regulator in as well and I'm at 13.7 now. Next step is fixing my exhaust leak then time to start the mega squirt build. Thanks all for the feedback
 

· Premium Member
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6,297 Posts
On a lot of older vehicles the light acts as a excitor for your Alternator.
not on the E30 chassis and later they don't, not sure about other makes and dont really care lol. but its a separate relay circuit on the E30 body.

Well turns out my problem was the ground wire from the alternator to the back of the cluster had an open in it so I repaired that and now everything is fine. Put a new voltage regulator in as well and I'm at 13.7 now. Next step is fixing my exhaust leak then time to start the mega squirt build. Thanks all for the feedback
good you got it sorted, i only just saw this but new it wouldn't be the cluster. You probably bumped the wire when you put the new cluster in and it made a better contact.
 
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