Ongoing electrical conundrum.....

[Guest Anonymous]

Greetings all. With winter here and it raining in Puddletown (Portland), I find myself needing to have the following items on on a regular basis- heater, lights, windshield wipers, turn signals, Radio. Just recently, I installed a new modern Radio/CD player and had some issues with amperage. I upgraded the alternator to a 318 and replaced my ground straps from the battery to the block and battery to the firewall.

Now I am having this issue. When the car is sitting at idle after complete warmup, I idle at around 800rpm. If I have the above items turned on and put my foot on the brake, the radio turns itself off and on. If I am driving, I cannot replicate the issue. Further, when driving, my battery guage sits @ 14. When at idle, it's below 12.

What's happening here? Battery? Ground? Gremlins?

Thanks.

Brett

'71 2002

[Guest Anonymous]

It should be putting out some amps @ 800 rpm... at least enough to keep everything powered. Is the battery OK?. The 318 alternator has an internal regulator--it may not be regulating properly and cutting off output at too high an rpm...

Happy hunting

Mike

[Guest Anonymous]

I don't think the brake lights should draw that much. I would go through that system, clean and check all connections. After that I would put a good meter on the line to the radio to see what is really happening.

Don't overlook the obvious like belt tension.

[Guest Anonymous]

I don't have the wiring diagram handy, but I'll bet the radio is on the same fuse as the brake lights. The large current surge when the brake lights come on makes the voltage on that circuit dip for half a second or so. (Incandescent lamps have a much lower resistance when cold, so the lamps draw a huge surge current for a fraction of a second while the filaments heat up.) Modern radios are more sensitive to low supply voltage than older ones. Your problem (not "issue") is common on E12 and E28 BMWs. On those cars the cure is to get radio power from a beefier fuse circuit and run it through a relay switched by the radio fuse.

Another aspect of the problem is the low battery voltage at idle. At what point is your battery gauge connected? Does it truly represent the voltage at the battery, or is it measuring the voltage somewhere downstream? If the voltage at the battery posts really is below 12, that is a genuine problem that needs to be fixed independent of the radio. If that 12 volts is being measured somewhere else, then there is a bad connection(s) between there and the battery.

[Guest Anonymous]

Hazard switch was designed for this purpose might help you. Also if you need a constant 12volts to power the preset and clock, I found only one inside the car and it is the one going to the cigarett lighter.

[Guest Anonymous]

Usually an alternator does not start to charge until 1000 RPM and sometimes not until 1200. That would take care of the low voltage at idle. My truck does the same thing and it idles at 600. You also get a fairly high load when the brake lights are applied.

In addition, there may be something wrong with the alternator. Have it checked out by a reputable shop. My 318 alrernaror does not do that.

Good Luck,

Mike (#87)

[Guest Anonymous]

The radio and brake lights are on the same circuit (so if your radio doesn't work, chances are you brake lights are out, too). I get the same condition - radio cuts out briefly when I put on the brakes. It's not really a problem; if it annoys you, move the radio to a different circuit.

Your amperage sounds about normal. Measuring across the battery, Molly shows 13.98 volts at 1500 rpm under light load and 13.1 volts at the same speed under high load. My voltmeter, which is wired at the end of a line, shows about right under light load but about 12 volts under heavy load. Try comparing your voltmeter reading to the voltage across the battery.

David Roach

"Molly" (Inka 1973 2002)

"Elmo" (Diamondschwartz 1991 325ix)