wiring

[86c20]

ok so i have a gremlins at work. i have a 85 k30 with the 6.2 and some time she wont crank at all. can drive it all day fine then she will not turn over. thought that something was getting hot so left the key on for 4 hours with the tunes on and she started fine drove it first thing in the am after stiting all night no start so its not some thing hot it seems. have done the wiggle test with no luck and i am just out for my mind right now. does anyone know what it could be or have the wiring dieagrams for it? any help or what to check would help also the clucth switch is by passed and has voltage on it when she dont start that is all i know. thanks, later mike

[bilfman]

Sounds pretty simple. Either a bad solenoid or starter to me. If either are wearing they can exhibit the 'work/not work' troubles.

[manimal]

Also check to see if the fusible links are in good shape. They will be down at the starter and on the firewall junction block. Also make sure the connections are tight at both.
And this has nothing to do with it, but make sure you have a starter brace since you have a 6.2. check out this place...http://www.dieselplace.com/forum/forumdisplay.php?f=20

[beamn7]

Check the connections on the ignition switch too. Down towards the bottom of the steering column.... Seen that alot....

[hatzie]

See the attached PDF for the 85 6.2L engine compartment wiring.
It's probably your starter. If you replace it be sure to get the right tail brace for the replacement starter you install Gear reduction is smaller and uses a different brace. Personally I'd find a reputable local big truck electrical re-builder (there should be a few in the Boston Providence area) and get your unit re-built. You know it fits and the field coils and armature weren't made in Asia or India.

I check, examine, and clean the power cables on my new acquisitions in this order;

Check all of the battery cable connections.
Unhook both grounds.
Clean the + terminals on the RH battery first. If it's stock the RH battery has 2 terminals and a special longer + mounting bolt than the other three. Unhook, clean with 220 grit emery cloth, brush off the lead battery terminal, coat the cable lug and battery terminals with Vaseline, and re-install. Do the same with the other + and then both grounds.
Unhook the grounds from the engine one at a time, clean the cable lugs and the mounting point then re-install making sure the star washers are re-installed on top and bottom of the cable lugs or added back if they aren't there.

Check the main + connection on the starter. The factory fusible link is hooked to the starters' Battery stud as well. Give the fusible link wire a once-over looking for blistered insulation etc. Make sure the copper starter stud, washers, lugs on the starter end of the + cable, and the terminals on the ends of the fusible link are clean and coated with Vaseline before you re-install everything.

While you are looking at the ends of each battery cable check that the insulation jacket doesn't look blistered or bloated. Oxides of copper have a larger molecule than straight metallic copper. The increase in mass is what distorts the PVC wire jacket. I have actually slit the jackets on battery cables and found that the pretty green and white oxide was making intermittent connection but there was no copper wire left.

I install braided copper grounds from the frame to the block near the motor mounts on both sides, from the frame to the radiator support, and from a bellhousing bolt to the firewall. This usually fixes many odd electrical gremlins.

[86c20]

hatzie i did some checking to day and i have found that i have no power to the starter. but i got5 the dieagram after i looked at it so i will have to dig into it on monday.
does anyone have the dash side diagram? i am really thinking its the key switch but just a though. i did check the starter wires and they are all in good shape will be going through all the wires on monday. thanks for the help guys. later, mike

[Wrecked1982]

my 81 c30 would sometime lost total power like this. i turned out to be simply the batterie termina.l had to brush the pole like hell cuz the first time i cleaned them it didnt work.

[hatzie]

I assume you mean there's no Juice at the big lug on the starter. This means your battery cable is not carrying volts.
Corrosion or... The + cable is shot. Or. Someone replaced the special double cable battery bolt with a short single cable one on the passenger side battery. It's been 28 years since she was new so...

[86c20]

sorry i should have said on the coil side there is no power. forgot to put that in there lol b+ side is hot at all times like it should be. and the long lug is there on the pass side this i know cause first time i had seen one like it. thanks, mike