f150 won't start on just 1 battery

[panasonic]

Yes on the meter hookup , no on the cranking, key was turned to the on position

Do the same exact test on the positve and negative cables again while cranking the engine over. See what the meter reads then....should be no more then .5 to .7 volts DC. (Which is 500 to 700 millivolts) Tell us what you find.

[pstephens46]

Did you have the battery switch set to both while testing?

Perhaps you need to check voltage drop to the switch while switch is turned to 1 and then 2. Issue may be in the "short" run of the cable there between battery and switch. Would explain why it would start when set on both versus 1 or 2.

[gsdanno1]

Would love to , what would the next test be

[99yam40]

the .5 volt Rod talked about is 500 MV
you are below that, so go on to the next part of test.

10 seconds of cranking is a long time on a starter.

[pstephens46]

Me either. Maybe Rodbolt can weigh in.

[gsdanno1]

9.1 mv , but just now I have 000.0mv key off , and 5.9 mv key off neg to neg ,and 163mv key on positive to positive. The more I check the more confused I become. Can't understand how there could be a polarity issue

[pstephens46]

Now voltage drop is -39mv key off. And -119 mv. How can I be reading a negative number

Reverse polarity. Try reversing leads .

I cant see the pics very well on my phone. Was that 9.1 mv or 9.1volts in third pic above?

[gsdanno1]

Now voltage drop is -39mv key off. And -119 mv. How can I be reading a negative number

[gsdanno1]

Going positive to positive from batt to batt switch I get -53 mv

[gsdanno1]

There aren't any connections on that run. It goes from the starter straight to the battery. From th et e to the switch . Everything cleaned and tightened again this morning

[pstephens46]

I think that 9.1 reading is telling. As long as the you are reading pos to pos. That should be an indication of resistance.

I would check any connections on that wire run. Back your lead up and take another measurement.

[gsdanno1]

Yes on the meter hookup , no on the cranking, key was turned to the on position

[panasonic]

"Next pics are voltage drop results , starting with the positive side key off , then on , then following with negative side in the same order."



Just to be sure, you said with the key "ON", meaning you where cranking the engine over while doing the voltage drop on each cable?

Also this is how you had your meter hooked up? (see attached diagram)

[gsdanno1]

here's the rest

[gsdanno1]

ok , here is the latest info with PICS !! 12.7 volts at battery , cranked the motor and voltage dropped down to 10.4-10.8 after about 10 secs . Checked again about 5 mins later , voltage 12.5 . The first pic of is of the horrible wiring in the console , I've had this on the list of things to get fixed , but something else always comes up. I may have to do it in order to diagnose what's going on. Next pics are voltage drop results , starting with the positive side key off , then on , then following with negative side in the same order. Battery cables are a continuous run from the motor all the way into the console , where I can't see what happens when they come through the rigging tube due to what's going on in pic 1