Starter/electrical question

[Tar356]

Sort of an odd question....

Should a starter motor show a current draw when it's not turned on?

Long story, but in chasing an electrical problem in a track car, I noticed that I'm getting a draw of roughly 8.0v on the main starter wire. This draw is present when the starter is static. The cable has been isolated and checked and it's not the cable. When I disconnect the cable, the draw goes to 0.1. Reconnect the cable, and the draw jumps up.

Typically a circuit shouldn't show a draw unless it's complete to ground.

I'm thinking the starter is failing somehow, going to ground and drawing power?

Ideas?

Thanks!

[Bob Kontak]

On the 911SC wiring diagram there is a wire that connects to the starter from the alternator on the same starter lug as the battery wire. Remove that alternator wire and test if your starter is still drawing voltage.

[Tar356]

Thanks for the reply Bob....

This car has a "total loss" system, there is no alternator.

[Bob Kontak]

I Googled total loss ignition. That is a new one on me. Motorcycles mainly pop up. Not a racer (me) though.

Your thinking makes sense to me. At first blush I would think there is a starter solenoid issue vs starter motor issue.

Try removing the ignition key wire (yellow?) to see if that is providing the "ground"

[Tar356]

We've isolated and checked every circuit(wire) in the car, and the large cable to the starter motor itself is the only one drawing power.

[Bob Kontak]

The large cable connects to the solenoid attached to the starter, correct? There is a solenoid? Just looking for clarification. I was wrong in the assumption about the alternator.

The solenoid is the gate keeper of juice. There has to be an insulation breakdown. Even if the starter windings were shorting to ground there should be no way for juice to get to the starter motor except through the solenoid - which is a heavy duty switch.

[911pcars]

Originally Posted by Bob Kontak

The large cable connects to the solenoid attached to the starter, correct? There is a solenoid? Just looking for clarification. I was wrong in the assumption about the alternator.

The solenoid is the gate keeper of juice. There has to be an insulation breakdown. Even if the starter windings were shorting to ground there should be no way for juice to get to the starter motor except through the solenoid - which is a heavy duty switch.

Fully concur.

Disconnect battery ground, remove the battery cable from the starter, then insulate the ring connnector with electrical tape. Reconnect the battery and measure source voltage at the starter end of the battery cable. Should be the same as at the battery posts. However, if there's a voltage loss (e.g.
If voltage is the same, then suspect the solenoid for either an internal short or other malfunction. Does it click at all? If no, it's possible the solenoid plunger is stuck in the energized position, thus closing the contacts and providing a current path into a malfunctioning starter motor (possible cause for voltage drop of 4 volts [12–4 = 8 volts]).

Sherwood

[Tar356]

I should have clarified that the starter works fine.

The reason for tracking down a short is that the battery is draining down about 3-4 laps into a race, causing low voltage to the ignition system, causing a misfire at sustained high rpm. After going over every wire/circuit in the car, the large starter cable is the only one showing a current draw. I'm assuming that with a cable that large going to ground, it would drain the battery fairly quick(especially with the other systems drawing power at the same time).

Bob: Sort of concur. The solenoid IS the gate keeper, but the power which turns the starter does not come through the solenoid. As Sherwood explains, the solenoid is sort of "switch" that closes contacts in the starter which completes the circuit from the large starter cable. The solenoid gets its power from the smaller wire.

Sherwood: I've been leaning toward your last comment about the contacts in the starter having some sort of problem.

I appreciate both of your efforts/input, keep it coming!

[304065]

The starter cable has two functions:

1) carries current from the battery to the starter solenoid, which when engaged by energizing the yellow wire, will send current to the starter itself, cranking the engine; and

2) carries current from the alternator forward to the battery. Modern cars actually have a wire from the alternator B+ terminal to the starter. This allows the whole system to be lighter weight because the starter cable serves a dual purpose. Think of it as the electrical backbone of the car.

Now I have a question: I know about total loss systems, even 16 volt setups. Are you saying that you have an alternator installed, and yet you don't charge the battery to avoid the horsepower loss? Or are you saying that you have no alternator in the car at all? If the last answer is yes, what kind of engine is in the car?

Anyway, it's entirely possible that you have current consumers in the back of the car that are feeding off the starter cable. We need more information about the car and its systems to understand this. That or friction has worn the dielectric cable sheathing thin and you have some kind of a short.

[Tar356]

304065: The system has an alternator, but not wired. There are no other "consumers" on the starter circuit...it's a straight shot from the battery cut-off switch to the starter. It's been checked and has no problems.

[304065]

Does the car still have the factory wire harness? What year is it?


How are you measuring eight volts? Between the starter cable lug and the stud on the solenoid? When you put your VOM between those terminals you get a draw of 8V?

[Tar356]

It's not the factory harness.

VOM was placed between the cable and the master cut-off switch. Showed 8.0v, then leaving the VOM in place, removed the cable from the starter, showed 0.1v.