All right everybody I got a weird one for you. I have an aftermarket radio that dies and restarts only under the very specific conditions of high beams on and brakes depressed. Any other combination of electrical gubbins and there isn't an issue...thoughts?

 

Sounds like a combination of an underperforming alternator and a low battery, voltage drops so low when you hit the brakes that the radio can't stay on.

 

I have a brand new 70A alternator that is running around 13v at idle with all accessories on. With that being said I had one night that the car dropped to 8v randomly on deceleration...so not out of the question. Battery is constantly at 12.2v and drops to around 11.8 on crank.

 

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That battery voltage at 12.2 seems good, 12.6 is ideal fwiw.

THe alternator should be charging at 14.5V, not 13. But given the battery staying at 12.2, only dropping to 11.8 at crank, I don't think the voltage regulator on the alt is your problem with the radio.

Often times when seemingly unrelated electrical things happen when you hit the brakes or turn on the headlights, it can be due to ground loops induced by corrosion. So it would be good policy to check ground connections to the body and to generally inspect and clean up corrosion.

 

Try taking out the fuse that controls the brakes lights. If the issue goes away, you found the problem in the brake light wiring.

 

Check the engine grounding from the battery to the chassis to the engine block (one of the trans bolts). Especially where the ground bolts to the chassis on its way to the engine.

The brake lights represent a significant current inrush and you may be causing enough of a voltage transient that the radio shuts off. Normally the battery acts as a way to damp this, but if there is a poor connection somewhere between the chassis and the battery then you may be overtaxing that connection.

How about when the HVAC blower is on?

 

Everybody thank you for your input was in fact grounding connections and bad battery. Cleaned up all my grounding points added some Dielectric grease and popped in a fresh new red top everything's been working great. Sorry it took me so long to get back to yall👍

 

Oh ack... my experiences with Optima batteries make me dislike them with a passion. They seem to fail if you let them discharge only once, and they are also very finicky with charging. If they have high resistance (due to being discharged) then they can let the smoke out in a literal and almost violent sense.