LB7 electrical gremlins

[02ilduramax]

ive been having some electrical issues on my 2002 lb7 and im stumped and not sure where to start first thing that happens is my gauge cluster will not work unless something is plugged in to the OBD2 port currently I am using a cheapo code reader and leave it plugged in once unplugged I have no oil pressure no rpm gauge no speedometer nothing. my second issue which I don't think is related to the first in my turn signals sometime they flash normal sometime flash fast sometimes the both flash at the same time and sometime the are illuminated but do not flash I switched out the turn signal switch with no luck has anyone seen or heard of either of these isues or maybe where to start

 

[Pure Diesel]

Check all the ground connecting points. Even if they look good, disconnect them, clean the mating surfaces and re-install. How old are your batteries? Have them load checked. Start from here and check back in.

 

[02ilduramax]

batteries are a few years old but both checked out good on 2 different load testers I will look in to grounds this weekend

 

[TheBac]

load test each battery separately. Grounds under the drivers door were always an issue on the early trucks.

 

[ironmax]

Isnt there a ground stud behind the interior drivers side fuse panel cover mounted on the body? As far as the turn signals, I would check the bulbs. Ive had brand new bulbs be bad and cause funky issues.

 

[dndj]

Agree about grounding. Referencing my 2003 schematic, the OBD2 connector behavior the OP noted is a big clue. Pin 4 and 5 are both grounds in the OBD2 connector, pin 4 connects to G200 which is a ground lug under the dash on the right hand side. Pin 5 connects to G203 which is a ground lug under the dash on the left hand side. When a device is plugged into the OBD2 connector, these 2 grounds very likely get bussed together. My guess is G200 or G203 are missing or not making proper connection any more, so the OBD2 device provides the missing ground. Parts of the instrument cluster ground through G203, but the instrument panel illumination lamps ground through G200.

Someone with 2002 schematics should verify all of this however.

 

[02ilduramax]

each battery was load tested separately and I will check on those 2 grounds and see what I come up with and check back

 

[dndj]

Isnt there a ground stud behind the interior drivers side fuse panel cover mounted on the body? As far as the turn signals, I would check the bulbs. Ive had brand new bulbs be bad and cause funky issues.

Yes. This should be ground G203.