2004 GPW

Video of the sound:
I bought a new battery today and installed it. It was a die hard silver. The old battery was a die hard gold. The terminals positive and negative are reversed on those 2 batteries for some reason. They look the same otherwise.
I connected the terminals backwards and the horn honked. The car wasn't getting power when the key is turned. The 100A fuse under the hood was blown. I replaced the fuse and the car starts up fine.

The issue is now the radio is making this clicky hum sound. It does vary with rpm. It only does it when the car is running. I'm wondering if replacing the head unit is the soliton. Anyone ever had this issue?

https://www.s2ki.com/forums/s2000-el...-637604/page2/ The last comment on that forum post sounds like it could be similar.

I kinda hate all the aftermarket oem single din stereo units. They look straight out of the 1990's.

*that pic is not my car but it looks just like that.

 

I can't pick out radio hum from what seems like ambient background noise. OEM radios are common Ebay items, many under $100. Photos of your car look good enough I'd want to retain it in as much original condition as possible including the radio -- but I don't claim this is a majority opinion.

Connecting the battery backwards takes some dedicated effort since the battery terminals are different sizes and should only fit the correct cables... (You just discovered this. Hopefully those reading along will take note.)

-- Chuck

 

I didn't actually tighten down the connections. I just touched the terminals backwards and it sparked instantly and the horn honked and blew that 100A fuse. If you saw the scenario you'd see how it could happen.

 

My guess is the alternator. Specifically, the voltage rectifier. The typical failure mode is half the recifier blows, so instead of a smooth DC voltage, half the AC current never gets.coverted to DC, so result is a spikey signal.

This typically causes visible dash light flicker (if you're looking for it). Coukd easily also cause radio hum.

If dash lights flickering, this is your issue.

Replacing rectifier is cheap. Around $25. Not too difficult to diy. A shop is just gonna wanna replace entire alternator, with a crappy rebuilt one, which will be less reliable than your well used oem one.

 

Sounds like you purchased a group 51 battery as opposed to the 51R battery (poles are reversed)

 

Maybe so. I didn't know there was a difference. I went to Advance Auto Parts and "the computer" said the battery they sold me.

 

I will look into the alternator rectifier. I haven't noticed any dash lights flickering but I haven't driven the car at night since the incedent.

 

I've had that RPM-related radio noise before. It could be a ground connection. Check to be sure the ones on the battery and the battery-to-chassis/body are tight. It's worth a try.

You can have AutoZone test the alternator — that test should be able to test the rectifiers. You'll need to remove the alternator first.

 

Good call on the grounds, a real possibility.

While that test would be definitive, its pretty easy to diagnose just carefully observing dash lights.

Unrelated to quote, both type 51 & 51R fit, and in some databases one is listed as correct, others say the other is correct. Our cables are long enough to fit either way.

 

I just fired up the car (at night) and turned on the lights. I didn't notice any interior dash lights flickering. I tested, with a multimeter, the voltage on the battery while the engine was running. 14.4 volts. I'm supposing it's either the head unit is damaged or the alternator. I hate to spend money on the wrong one. Thanks for your input and advice.