We have a 2002 convertible, basically stock. ( honker air intake,, cat back B.B. exhaust,, thats all )
It didn't start other day, engine cranked over at proper speed but didn't fire of and start. Put booster battery box on it. It instantly started. We went to dinner 5 mins. away.. Didn't restart after dinner,, same thing, turned over fast but didn't fire off , jumped it, started right up, drove back home fine. No codes or service lights. I put volt meter on it,, 12.3 volts. So put 6amp charger on it over night. Didnt re start in the morning, battery tested 12.3 then also, so thought battery must be not preforming good enough. I put 50 amp booster on it and fired right up, so drove it to my other garage and parked it till I could get a new battery. Fast fwd to today. Got a new battery, ( 760 CCA ) Installed it and now dash lights flashing, a buzzing sound near battery & eng. and engine turns over VERRY slowly. New battery tested 13.2V. ( Old battery tested 13.1V after 5 days with tender on it ) So , I tried adding my jump box ( @full charge ) and same reaction, slow starter,, guages flickering. All lights are working, power windows working, radio works . Fuses all check good. (both boxs) ..
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Am I chasing a bad connection somewhere, possibly a ground somewhere. This car is super clean every where, but I realize unseen corrosion can exist..
Gauges/ Dash info won't let me check for codes. Would OBD2 reader work?
Any help chasing this issue is appreciated, and thanks to all in advance 🙏. We have plans to take it to Nashville Wed,, but seems unlikely now. Might have to re pack smaller bags and take our C3 for the trip...HELP

 

Check your battery cables at the engine bay fuse box, lift the cover and you will find where the positive battery cable connects to the fuse box, and the secound cable which provides power to the interior fuse box. Also check the smaller gauge negative battery cable which terminates under the battery tray. Hope this helps. Make sure your battery cables terminals are nice and tight.

 

If you have a DMM and a 12 volt test light and know how to them I’d do a voltage drop on the starting system if the car is cranking over slowly…let me know if you need instruction on voltage drop testing… you will need to get under the car for this…helps to have leads with alligator clips on them.

 

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. Thankyou mmartinez,, I certainly will.

 

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.I do believe that is part of the problem, as well as to the gages,,, thanks 😊

 

Then you’ll have to test and not guess…this test takes a few minutes.

 

Exactly,, im not wanting to guess, and start 'throwing darts and see what sticks', just hoping to start in a intelligent methodical way, and not 'spin my wheels' too much chasing the issue. I appreciate all the educated people with experience willing to assist. 🙌

 

First thing is to ALWAYS start with the battery and then the “Triple D”…Data Driven Diagnostics”.

 

Hay everyone, I want to thank you for the direction freely given to help me out with my issue.
I disconnected and inspected the five grounding locations under the hood area. Every one of them was "day one" clean. Even so, I did clean them with a brush and proper contact cleaner. Then opened up the connectors containing multiple ground wires to inspect for hidden corrosion but again found them "day one" clean without hint of problems. I also cleaned them anyway to be positive. Still no chance in starting.
. . I did more research into possible causes and decided to pull out the ignition key switch and inspect the " breaker points " to look for ark marks or burned spots. A couple looked suspect but not as bad as some pics i saw of others. I polished all of the points with super fine sandpaper and adjusted the spring tension on all of them as well. Reinstalled the switch and gave it a try again. IT STARTED RIGHT UP AS NORMAL. Gages working as normal again as well as information center display all working as it should. Seems the issue was the ignition key switch. We got 140k trouble free miles from it,, hopeing for another 140k mi before it needs attention again.
My wife is so excited to have her baby back on the road. I'm happy as well....

Thanks for good direction as well as older posts here on this form for great information!