Busted Alternator Fuse - Symptoms?

[MrJones98]

A couple weeks ago, my battery would not hold a charge. I put in a new battery and still no luck. I took it to Lexus (had no problem driving it once it was jumped) and was listening to the radio on the way down. They told me my alternator fuse was busted and I needed a new battery. I brought them a new battery (since it was under warranty) and they replaced my alternator fuse.

Things seem to be better but now my speaker is muted, my CD changer seems busted (makes some loading/clicking noises when I insert the cassette but can't select CD from the head unit), and my phone doesn't turn on at all. From searching, it seems that the phone may be affecting my radio so that is a separate issue.

When I asked my Service Advisor about everything, he sounded fishy so I wanted to know what the alternator fuse sits between. I assume that it sits between the alternator and everything else - so a blown fuse would look like a blown alternator. If this is the case, then I wouldn't have been able to drive my car down to the dealer with both a bad alternator fuse and bad battery. He also said that nothing was working when they got the car, that all of the lights were on in the dash and that my radio wasn't working. I'm not trusting anything he says and want more understanding of the system.

Right now, I'm thinking they did something to my electrical that busted the phone/radio and they are trying to hide something by saying that nothing was working when I brought it in.

Any help is greatly appreciated!

Again, a 91 LS400...

[VincyRay]

That's not the way it happened when my alternator fuse went out on my SC400.

I was driving it, and talking on my cell phone (not attached to the car) and not really paying attention to the car. When I got off the phone, the first thing I noticed was that the radio had turned itself and would not come back on. Then I noticed that my dash lights had gone out. I was still able to drive fine, but only had another few blocks to get where I was going. When I got there and turned off the car, it would not start again! The lights and horn worked fine, leading me to think it was something with the switch. After I had it towed home, I noticed that the alternator fuse had blown. I put another in and it blew as soon as I touched the new fuse and litteraly burned my hand (guess I should have thought to disconnect the battery). Turned out that my alternator had a short somewhere on the inside.

Unfortunately my car hasn't been right since though, so I'm not the best one to give advice about this...

[Vadette23]

I have a 1990 Lexus 400ls. Recently put new battery. Then had to replace alternator. Been running fine. Now doing same thing. Won't turn over. Is it a fuse or what ! I had corrosion on positive cable. Cleaning it with coke !I'm waiting for my jump box to charge. Need help. Thanks !

[RX400h]

Did you check the negative cable? A bad ground could prevent proper charging.
If you can't find anything obvious, you may consider taking it to an Auto Electric shop.
Solving electrical issues is their business.

[paulo57509]

On 3/24/2022 at 6:47 PM, Vadette23 said:

I have a 1990 Lexus 400ls. Recently put new battery. Then had to replace alternator. Been running fine. Now doing same thing. Won't turn over. Is it a fuse or what ! I had corrosion on positive cable. Cleaning it with coke !I'm waiting for my jump box to charge. Need help. Thanks !

Let's see....

Q1 - Why did you replace the battery?

Q2 - Did you disconnect the battery when you replaced the alternator?

1.  Put a volt meter across the battery (if you have one).  What's the meter read?  It should read >12 volts.  If it doesn't, use your jumper box or recharge the battery with a plug-in charger and see if the starter cranks.  Once you get the engine running, put the volt meter across the battery again.  It should now read close to 14 volts (confirms the alternator is working).

2.  Remove the negative cable first and then the positive.  Clean the battery terminals and cables with a brush:or a piece of fine emery cloth.  Re-connect the cables; positive first then the negative.

3.  Unlikely this would happen (would be a crazy coincidence) but there is a starter relay that can go bad.  When this happens the starter won't operate. 

[Lexus Owners Club]

Agree with the above suggestions....

Definitely check the earth cables and that the connections to the chassis are clean and tight

Also, as suggested, the battery terminals need to be shiny clean to ensure the current flows freely

Start there and see how you get on and let us know how it goes