The Stovebolt Site Forums The Shop Area The Electrical Bay Backwards battery?

Hi All
I have a question on my truck’s wiring that I wanted to run by the experts here. I bought my C3100 ½ ton ( ‘55 first series) with a 235 in early Winter and drove it home without incident ( 40 miles) and parked it in my garage until this weekend.

Upon having trouble starting the motor again (would not crank) I rolled the truck out to my driveway so I could get to the passenger side (blocked by garage) and immediately thought my battery was bad. I had it on a tender, which reported a good 13.3 volts and then noticed what I think are backward cables from the battery to the block and starter solenoid.

My truck was converted to 12V, but the guy I bought it from said it was still positive ground, which really confused me a bit, so I took a look. The cable from the battery minus leads directly to a connection on the block and the cable on the plus side of the battery leads to the solenoid. - looks like regular negative ground to me so far. The issue however is that the colors of the battery cables were reversed. I.E. the red cable was connected to batter minus and the block and the black cable went from battery plus to solenoid. The black cable even had a “Positive” tape label on it.

This got me thinking that the previous owner was confused since it appears to me to be conventionally powered negative ground 12V, but I began to wonder if something along the way got things reversed.

To begin my testing for why it would not crank, I marked the connections, removed the battery and had it load tested to insure it was OK and it was, ( 550 cranking amps — battery also appears pretty new) and verified twice I did not reverse the connections from original when I reinstalled. The starter still would not crank the engine. I also removed the other end of the battery connections at the block and solenoid and cleaned them nice and shiny with a combination of wire brush and coarse sandpaper. I had a friend watch as I hit the starter and the solenoid did function but the starter would either not plunge to start , or engage, turn a 1/4 rev or so and immediately withdrawal. While this process was occurring, the ammeter on the dash was pegged on Discharge.

I am now guessing that the starter motor is bad, but it led me to think about besides the starter motor running backwards?, would there be any other way to determine if the wiring is backwards, or that it is positive ground? — While I drove it home after purchasing it, the ammeter showed slight charging as I would expect and that when I turn on the headlights while parked, for example, the ammeter would show slight discharge. If I remember how the ammeter works correctly the direction of the current controls the ammeter so that I would expect a reversed ammeter if my connections were backwards.

If I can confirm a regular negative ground 12V system on my truck, I will certainly reverse the cables (good excuse to buy new ones far as I am concerned)
Any other ideas out there? — I am looking how to fix my starter as well..

Thanks to all who respond - hope to not let the magic smoke out anywhere

Joe Finkelstine

The only starter motors that will run backwards with reverse polarity are the ones made with permanent magnets instead of field coils in the housing. That didn't begin until the mid-1980's when the manufacturers got on a weight-reduction crusade.

If the solenoid is hammering in and out as you hold the key in the start position, you have a bad "hold-in winding" in the solenoid. Unless the starter is fairly new and in good condition otherwise, just swap starter, solenoid and all for a rebuilt unit. The cost won't be much more than a replacement solenoid.
Jerry

If your truck is a Chevrolet it has been negative ground all it's life.

I'd have the starter checked by a good independent shop.