M1078 starts runs for minute then loses electrical power

[Thomas_G]

Have a 1078 built 2002 that was running normal, parked it then when go to start it runs for a minute than can hear a click then truck loses power.

relay shorted?

 

[NDT]

Could be dozens of issues. Time to break out the voltmeter and starting at the batteries, see where battery power is dropping off.

 

[Thomas_G]

Truck has brand new 6TLs, once you cycle ignition switch, starts up normal then repeats, click, no power

 

[coachgeo]

Truck has brand new 6TLs, once you cycle ignition switch, starts up normal then repeats, click, no power

pull your grounds and clean them. then test. next step might be to then pull relay or two and replace with fuses... replace if no change..... and try again till you narrow down if.... or if not a relay is bad... My guess it is either relay or ground

hmm.. should add... when pull, clean/reinstall grounds.... also clean the terminal connections to the box under the spare tire (battery load protection thingamagigy)

 

[coachgeo]

has been said on F.book group that the grounds for an A0 are below. Suspect same for an A1?

-alternator to frame
-starter to frame
-cab to frame behind grill on pax side
-under pdp on right side

 

[Suprman]

Does it have the disconnect relay? Box to the right of the batt box.

 

[Ronmar]

Well if it is an A1, the LBCD could be sensing something wrong and disconnecting. the truck is supposed to keep running thru this though so it may be something else in conjunction with this. You need to connect a voltmeter to the Ground, 12 and 24v test points at the power dist panel in the dash and watch the voltage while running. It will of course dip while cranking, but it should come right back up and remain steady(14.2 and 18.5 if alt is online). It should stay steady even after the truck shuts off. If it doesn’t the problem is between there and the batteries or a bad ground between the ground test point and the - terminal of the batteries.

if the voltage stays steady at the PDP test points even after the truck quits, it is likely a bad relay or circuit breaker. Say a 12v relay accidently plugged into a 24v circuit that has had enough and overheats and fails after a short time...