Lights dim when electrics used.

[Mister Peebody]

Originally Posted by fyr145

Could be any number of issues. Lets look at a few of these.

3. Bad or loose Ground(s): Another remote possibility is a ground wire is not secure to the frame. Check all ground locations starting with the engine, then the negative cable on the battery, and so on.
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My vote is with #3! Corroded grounds will cause all sorts of strange issues.

[smileynialley]

thanks for the replies,
I have had a look around the engine bay and there is nothing obviously loose or corroded etc.
It seems like the alternator can't produce enough power to power everything in the car so when you use the windows or brake lights etc, the headlights and cabin lights either dim or cut out altogether and the stero cuts out.
No affect on the engine though.

[fyr145]

Ok then, if you have ruled out #3, then the next thing I would check is the battery then the alternator.

As I stated earlier, get a load tester or you can go to an AutoZone, O'rileys, checker, etc. and have them put their unit on the battery and check it. The load tester simulates having various electrical loads being placed on the battery by them flipping a switch or turning a dial depending on the type of tester then seeing if the battery can still maintain proper output even with a big load draw.

The other test is to check that alternator. just because you see the serpentine belt going around and spinning the pulley on the alternator doesn't necessarily mean that its putting out a charge to the battery. As stated earlier as well, most late model alternators are now built inside the alternator. (I upgraded my stock alternator from the factory 145 amp to a 200 amp because I had added the factory brush AND roof lights.) In the old days, the regulator was a separate unit and if it went faulty or bad, you could simply change out the regulator. Not any more.

The only other issues that I can think of if its still doing it after completing the previous steps mentioned above, is to go on a search for any power wires or connections to your accessories that may be touching or possibly arching on the body. Or worn insulation from being pinched or rubbing on something from vibration. Typically, when these issues occur, it would cause a short and blow the fuse.

Sometimes people tie all their accessories into one power power outlet or line. When all these are being used, the outlet cannot support all of them simultaneously thus causing a voltage drop.

Keep us posted on how the battery and alternator testing goes.

[LoJac963]

There should be other frame (chassis) grounds also not just what is obvious in the engine compartment.

[fyr145]

Thats true...............I forgot to mention that.

stupid me........ my bad.

Thanks LoJac

[HUMTECH]

One other thing, still related to testing alternator. May be putting out but if one diode in alternator fails then it will only put out 2/3 of its regulated output, 2 diodes out 1/3 charge. Something to keep in mind when testing alternator output.

[smileynialley]

The battery was replaced last year. It starts first time no issues so the battery is good.
I thought it could be a bad earth/ground too but the lights dim when the windows are activated too. Does anyone know if the windows and the brake lights happen to share an earth?
I also mentioned that I've noticed a whirring noise coming from the front of the car which gets faster as the revs go up, I'm wondering if this is an alternator problem.