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Battery Light Question


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Posted

So tonight I got the motor to fire again after some major front of motor work. The problem is that I can't start it using the standard ignition. I have to run a manual start button from the battery to the starter.

 

I suspect the alternator circuit as the problem. When I put the ignition to run, the battery light id off. Doesn't that indicate a problem? Does that also disable the factory starter circuit?

 

Thanks for any help,

-bj

Posted

So I think my alternator is toast. I started the car and I'm only getting a reading of 11.75 volts at the alternator terminal. I've pulled it off and will have it tested tomorrow.

 

-bj

Posted

Sounds low, but I'm not sure that's the starting problem. A car should start and run (for a while) without the alternator at all. The ignition switches often go bad on these cars. Try wiring in a starter button. Keep at it! 33 days 'till Gateway!

 

I was under the dash today removing excess wiring, and took off an important lookig box. When I found the car runs w/o it, I ran the part # - it's a "cruise control amplifier" - one more part and associated wires I can remove & toss.

Posted

I'm sure you did not do this but i will tell you what i did on a engine R/R last year.

 

I ran the wrong wires to the starter and ALT. they seemed be be correct but were wrong. so make sure you have the small blue wire going to the alt. and the red (I think it's red and black) wire going to the starter. both of these wires have a large gauge wire with them for the large posts on the starter and alt.

Posted (edited)

I don't know how the alternator died, but I'm nearly sure it is dead. I've checked as much of the wiring as I could. I know the main lead, the red wire, is good. Anyone know where there little wire with the 8mm bolt goes?

 

I'm going to order a new alternator in to morning. We'll see if that take care of it.

 

-bj

Edited by Guest
Posted
Sounds low, but I'm not sure that's the starting problem. A car should start and run (for a while) without the alternator at all.

 

 

I'm 100% sure that's how it is running, now. It will start with a remote start button jumpered between the battery and the starter. In fact, there is so little draw on idle, that I bet I could run an entire sprint race without a alternator. I think I'd feel a little better with an alternator, though.

 

-bj

Posted

Just dug up this old post:

 

did you get the 2 small wires on the alternator crossed? The ground and the blue exicter wire? The alternator light must come on with the key or it will not charge and this may be why you get no signal to the starter solinoid? This would make sense as to why the gauges all drop off as they are being grounded out, the starter gets no signal, and you get no charging. If this is the case you better check fuses as well.

 

2 small wires? I only seem to have one. Was this a difference between earily and late cars?

 

-bj

Posted

There's a two-wire connector in the engine bay, around the driver's side firewall, up top, behind the brake booster... One of them is for the starter solenoid and the other is for the alternator. I want to say it's a large red/black wire for the starter, and a smaller blue wire for the alternator. If this is unplugged, the starter switch will not work, and the battery light will not come on.

Posted
There's a two-wire connector in the engine bay, around the driver's side firewall, up top, behind the brake booster...

 

I found them and everything is good there. Actually, last night I figured several things out.

 

1. Got new tach working. Ended up being total unrelated. Just needed a clean ground.

2. I got the ignition working. Turned out one of the leads on my push button start was loose.

3. I had the alternator tested. It passed the tests at AutoZone.

 

What is weird is that I still don't get the battery light when the car is in run, and the alternator won't charge the system. I've checked the battery light bulb and have even replaced it. I have also swapped in my original yellow gauge.

 

At this point I'm leaning towards a ground issue. I think I'll go ahead and order an alternator today, just in case.

 

Anyone have any other ideas?

 

Thanks,

-bj

Posted

So I've been going through wiring diagrams. It looks like a simple circuit. Here's the main power system consisting of the alternator (generator), starter, and battery:

 

main_power.jpg

 

 

Here is the cluster on the dash:

 

cluster.jpg

 

You'll notice the blue wire runs between the alternator and the bulb on the dash. I've verified the connection at T21, but still need to find T1a. The other bulbs in the cluster illuminate, so the ground is good at the cluster.

 

So the bulb could just be a wiring problem, but the other important factor is that the alternator isn't charging the system. With the car on but not running, I see the battery voltage at the B+ terminal on the alternator. This tells me that the loop from the battery to the starter to the alternator is good.

 

So what's this leave me with? I see three possibilities:

 

1. AutoZone was wrong and the alternator is bad. I've got a new alternator on the way just in case.

 

2. Bad ground at the alternator. Not likely because the thing bolts to a huge metal bracket that bolts to the block. I can test this by running a temporary ground wire to a know good ground point using one side of a jumper cable.

 

3. Bad connection on the blue wire to the bulb. This should be easy to test as well. Just jumper in a 12v supply. I've read that if this circuit is open, the alternator won't output a charge. It caused a problem because if the bulb burned out, the system wouldn't charge. I'm guessing this is handled in the voltage regulator in the alternator, because I don't see any other components in the loop.

 

So am I missing anything?

 

-bj

Posted

I think I finally figured out my damn wiring problem. I don't know what the German electrical engineers where smoking when they did the factory diagrams, but I want some!

 

Here my simple diagram (sorry for the MS Paint drawing):

 

944_Main_Power.jpg

 

 

So when you click the car into Run, it sends +12v down the black wire to the battery bulb in the cluster. (Why would anyone use a black wire to indicate switched +12v is beyond me.) Then because the bulb is in series with the alternator, the D+ terminal is sent +12v via the blue wire. This circuit completes through the alternator's ground. The entire purpose of this circuit is to prime the alternator.

 

Now when you turn the key to Start, this engages the starter and the motor spins, thus spinning the alternator. Once the alternator can put out enough power to keep up, it kills the D+ circuit by removing the ground connection and starts outputting ~+14v on B+. This turns off the bulb in the dash.

 

My problem is with the blue wire between the bulb and the alternator. I can't get continuity across it. It seems to fail somewhere in the main relay board. This circuit doesn't go through a relay, so it is probably just corrosion. So, tonight I'm going to bypass this area by directly wiring the blue wire that goes through the firewall (which I know from testing is good) to the bulb.

 

We'll see...

 

-bj

Posted
Good work BJ. your knowledge of electrical workings is impressive (far beyond mine!). We may have to appoint you as the official electrical gremlin guru.

 

I'm guessing an admin hit edit instead of reply. Whose quote is this?

 

 

Anyway, my diagram worked out, and I was able to get the alternator working! In fact last night was very productive. I also rewired the tach, cleaned up the under-dash wiring, pulled off the throttle body and adjusted the throttle position sensor, adjusted the idle, adjusted the front brake pistons orientation, installed the front brakes/pads/hardware, installed the front stainless steel brake lines, rechecked the timing, and buttoned up the front timing cover.

 

That's not even the exciting part. The exciting thing is that we got an extended test of the motor. We let it run long enough to get up to temperature. The oil pressure looked good, the new fans came on when they were supposed to, our idle fluctuations from a vacuum leak are gone, no coolant was leaking, no oil was leaking from the new seals, and the new oil cooler felt warm.

 

Speaking of the oil cooler, that thing really works. It took forever for the motor to get to temperature. That's the weird thing about these motors--they have an internal oil cooler that the water cooling system flows around. So when you ad an external oil cooler, it is actually a secondary unit. It also cools the oil so much, that it can actually start taking heat out of the water cooling system, too.

 

The other thing about the new oil cooler is that it's also the only trouble spot with the motor. There is a small oil leak from one of the fittings. Shouldn't be too big of a deal to fix, though.

 

All in all, it was a great night.

 

-bj

Posted

That wire the blue one is called an exciter wire. It energises the alternator so that it can produce power for the car to run on. Your car should be charging about 13.7 VDC. Running you car on just a battery is not a good idea. Your ignition requires 12 VDC to operate. Once voltage drops below that voltage (12 VDC) spark is affected, hense power output ect ect ect. Not to mention gauges not working properly and wipers if you need them.

Hope to see you at Gateway Bj. I have almost got my car ready as well.

Posted
Your car should be charging about 13.7 VDC.

 

That's exactly where I'm at: 13.74V with my multimeter.

 

 

Running you car on just a battery is not a good idea. Your ignition requires 12 VDC to operate.

 

Agreed, that why I patched in a new exciter wire. That fixed it right up.

 

Hope to see you at Gateway Bj.

 

I'll be there. In fact I'm planning on being at Gateway even sooner than that. I'm doing 3 days of testing at Gateway the weekend of the 4th-6th. The local PCA is having an HPDE that weekend. I can wait to get this car back on the track!

 

-bj

Posted
I'm guessing an admin hit edit instead of reply. Whose quote is this?

 

'twas me

Posted

Getting a jump on the compition and learning the track in the 944. Nice

Posted
Getting a jump on the compition and learning the track in the 944. Nice

 

 

It's my home track. I did 12-14 days there last year. Most of them in the 944. Of course my 944 is barely the same car it was last year. I just want a chance to learn the car again.

 

There is also a Wednesday afternoon open test day at Gateway on April 16th. I plan on doing that, too.

 

-bj

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