1955 12v starting issue

[mplamothe440]

I have a '55 T-bird, that has been converted to 12 volts (conversion done by a prior owner). Last week an issue started were the engine wont turn over or turns over a few times then stops. Ocassionally I can get it to start but not reliably, car was running fine before this issue (no warning signs that battery or starter were beginning to fail). I noticed that the negative terminal on the battery would get very warm when it would turn over. I jumpered the positive batt cable directly to the starter power cable, the starter worked fine (did this for 5 seconds), negative terminal did not get warm. I assumed then that problem might be with starter relay(mounted on fire wall) or the ignition switch. I replaced both, still have the same sympton. I cleaned the batt negative cable ground (batt is mounted in the trunk), still fails. I disconnected the power cable to the alternator as well, still fails. I'm out of ideas any and all suggestions would be appreciated, thanks.

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[mmusgrovetn]

Check the fuel cap. Take it off and see if it starts. Needs to be vented.

 

[pltmgr]

Id recheck all the cables and connections and grounds. The battery should be stress tested. Just because the ignition switch and starter relay are new doesn't mean they are working correctly.

Im confused in regards to the gas cap affecting your situation.

 

[Tom Alpers]

first thing is... are you SURE the battery is good? If not, get it load tested. Assuming battery is good, any part of the power cables/parts in the high amp circuit to the starter that gets hot is a spot with excessive resistance. Even 0.01 ohm is too much when you are pulling nearly 200 amps, it would drop the 12 volts down to 9..... So check all connections again. Sometimes the cable clamp looks good but the wires inside are no longer making good contact. It is also possible that you have a worn out starter... dragging armature or worn out brushes.. sometimes works, sometimes doesn't. To troubleshoot this stuff you need to use a voltmeter so you can measure voltages at various places when you try and start it.