Bad Coil or Bad Ignition Box?

[texas1al]

I just put my rig back together after some major bodywork and I've got a problem with my ignition system. I've had the TR upgrade and nutter bypass installed without issue for 7+ years. I installed a new battery and new cables all around including fresh grounds to the engine, chassis, starter and body. After some cranking, the engine fired up fine, but then when I went to start it again the next day, there was nothing. The symptoms are typical of a bad battery, but I had the battery tested under load and it's fine.

Here are the symptoms - when I turn the key, there's a click from the starter solenoid/relay and then the volts on the dash gauge go to zero for a couple of seconds before popping back up to 12 or 13. All the lights and accessories shine bright until the dreaded click when they go out and then come back along with the volts on the gauge. I had the wifey do this a couple times so I could get closer to inspect and I noticed that when she turned the key from off to on (but not start), there was a intermittent buzzing sound coming from the coil for a second or two that sounds suspiciously like an arching spark. I'm guessing the coil is bad, but it's only 7 years old and it was a good quality Borg Warner unit. Could a bad coil drain enough power when trying to start that it diverts power from the starter & shuts everything down for a couple seconds or is there another likely culprit like the ignition box (3 years old) or something in the wiring?

Thanks
Al

[CJ7Taz]

Originally Posted by texas1al

Could a bad coil drain enough power when trying to start that it diverts power from the starter & shuts everything down for a couple seconds or is there another likely culprit like the ignition box (3 years old) or something in the wiring?

You’d be blowing fuses or melting wires long before the coil could pull that much power.

You’ve got a bad connection somewhere. Clean and check the battery cable to post connections and the ground connection.

[CJDave]

Is there any chance that you have the small wires on the solenoid switched around? The "S" and the "I" or whatever it is that they are marked?

[Jim_Lou]

You have a bad battery cable connection, at the battery, the solenoid, or the ground cable on the engine. If you've taken the battery out to have it tested, the bad connection is probably at the solenoid. If you try to start it, let the voltage go to zero, and then turn the headlights on (they won't light) the bad connection will feel warm to the touch, if not hot.

It also could be a faulty cable.

[texas1al]

Thanks for the quick replies gentlemen. A bad connection makes sense, but since I've gone through and replaced all the cables including the grounds, I thought I could scratch that from the list, but I'll be sure to check them all again since that seems to be the consensus.

Thanks
Al

[Jim_Lou]

If you have a volt meter, a good way to check them is by looking for a voltage between any two points on the circuit. Engage the starter and place the probes on two spots, such as a battery post and the terminal clamp on the post. A couple of thousandths of a volt is OK, but more than that is a problem. This only works when there's a significant load on the system, such as engaging the starter motor.

[texas1al]

Problem Solved - It was indeed a bad connection. The cables and grounds were fine, but the battery cut-off switch was bad. Once again, this board has saved me from my own stupidity before I started throwing parts at the problem.

Thanks for the help.

Al