Electrical Help

[dlcully]

I have a 98 and I am having problems with the electrical system. I have a valentine one radar detector in my car. When it is hot outside, with the radar detector on, and I hit the brakes while the car is in drive, the voltage on the battery goes down below 13 and into the red. when this happens, the radar detector flashes off. When I hit the gas to take off, the voltage goes back above 13. Then the radar detector works fine. I have recently replaced the battery and had the alternator tested, and they say that the alternator is good. Can anyone help with this. Thanks

[04goatinmass]

i get surges like that as well but not that bad.what do you have running in your car(speakers amp or anything).did you get the right size battery doesnt hurt to go with a stronger ccamps.maybe the alternator is weak and when they tested it it was working normal at that time.did they do a load test to it.mine used to go below the 13 before then i bought a overrated battery and have no problem with the level but i still get surges.your surges sound like your fan turning on to keep the temp normal.that draws alot at startup plus you got your brakes lights on and stuff.just seems like your drawing to much amps at that givin time and your battery or alternator cant handle it.good luck let me know how you made out

[dlcully]

I don't have anything else running but the stock stereo. I have had the car since 2000 and have been having this problem since then. So I would have thought that if the alternator was going bad, then it would have gone out by now. But it does get pretty darn anoying at times.

[Transam388]

On this note, what is the highest output alternator the F-bodies can take and who makes the better ones? Mine also does this. I notice more at night as the lights even start to dim for a second and then are OK. I have an underdrive crank pulley so the alternator is not spinning as fast which is some of the issue but it never used to have the lights dim. It is also just a quick dim and not like when I am sitting at a light the entire time it is dim. Good luck with it though man as I know it is somewhat annoying.

[04goatinmass]

i read in a post on here about a pump that turns on which draws alot as well.i would try the alternator.could even be a loose belt