Battery Warning Light

[matthew_w]

On my way to its MOT, I noticed that when the front screen demister on my 2.8 auto Galaxy was on, the battery warning light came on. Nothing else - full lights, rear window demist, electric windows, aircon/heater, all of the above together - caused the light. Front heated window on - on comes the light. Off - the light goes off.

 

The garage diagnosed a faulty alternator and had it rebuilt and charged me

[Ivor_E_Tower]

Well, the fault is there, so straight back to the garage for a refund for unnecessary work. Could be an earthing problem from the front screen heater as this is the only thing that seems to make your warning light illumnate.

[Guest j_mchattie]

Just sounds like a wiring problem. Your alternator is fine by the sounds of it (and didnt need replacing, any decent garage would have known this).

 

I think they were hoping for a little extra output from the new one to turn off the light.

 

I would think its a short somewhere, check your fusebox is clean and that the fuses are the correct values. Heat from an under-rated fuse can increase resistance, and therefore mess about with the voltage sensor (depending on where in the chain it is).

 

Id do some wiring checks.

 

It might be that the demister is simply drawing more than it normally should be, and that the battery light comes on to tell you this (not actually indicating that there is an excessive power drain from the battery, but advising you that the demister is faulty) Take a flick through the manual to see if this is the case.

[Guest vr6galaxy]

It could be that the excessive current draw made by the screen is affecting the voltage to the clocks and bringing on the light? check the connections for the heated screen, especially the neutral connections above the head lining above the rear veiw mirror

[johnb80]

It would be interesting to measure the voltage between the battery -ve and the engine itself with heated screen on and heated screen off. The alternator light will glow when 0.6v or more appears here. Try temporarily putting a wire from battery -ve to the engine, also check all of the small -ve wires connected to the battery, a bad connection here will give similar problems.

 

Excessive load would cause fuses to pop, not lights to glow.

 

Caio - JB

[johnb80]

It would be interesting to measure the voltage between the battery -ve and the engine itself with heated screen on and heated screen off. The alternator light will glow when 0.6v or more appears here. Try temporarily putting a wire from battery -ve to the engine, also check all of the small -ve wires connected to the battery, a bad connection here will give similar problems.

 

Excessive load would cause fuses to pop, not lights to glow.

 

Caio - JB