low voltage and no crank
 

this 88 4.0 is killing me! i can't get it to crank. the battery gauge in my dash shows about 9.5v but when i check the battery with my dvom its showing 12.4. the jeep wont even turn over. its acting just like a dead battery. i used my jumper cables to jump from the ground post on the battery to the ground on the block and the positive post to the starter. nothing changed so that eliminates the battery cables being corroded or anything. i have no clue what else to try. please help!!

Are u hearing any noises a click anything?

Turn the headlights on and then watch what they do when you turn the key. Also, are the terminals tight on the posts? If one was loose, or corroded between the terminal and post, then your jumper cable test wouldn't be valid. It could quite possibly be a weak battery, too.

battery tested good. terminals are tight. lights die just like a dead battery. also forgot to mention that i tried jumping it with my other truck and it acts exactly the same with a running cummins hooked up to it. its tripping me out!

Use the volt meter to check power at the large wire that goes to fuse box. Should be same as battery voltage turn something while your doing to put a load on the wire if it's not the same or very close with in .02 volt if its low the wire or condition is bad start there and let us know the results

I mean connection not condition :)

Was the battery load tested? If you show 9.5 volts during the attempt to start, that is not enough. Bad battery. You may be dropping voltage somewhere if the battery is good.

During the jumper cable jump connecting to the starter positive post will do nothing unless you turned the key to start. Using that technique you connect to the starter solenoid terminal. This engages the solenoid which then should crank the engine. Try a jump from your battery positive post to the solenoid terminal. See if the starter engages and cranks the engine. Do a voltage test at the starter solenoid terminal. Have a helper turn the key to start. You should read battery voltage with the key held to start.