Newbie in desperate need of help..98 gmc electrical problems

Discussion in 'GMC Truck Forum' started by tanman34, Dec 1, 2016.

  1. tanman34

    tanman34 Member

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    Hi everyone came across this site trying to figure out whats wrong with my truck and it seems some of you guys know your stuff. So I figured I would post.
    Here is the problem. Drove my truck home from work couple days ago right at dark. Everything was fine ac lights starting no problems. Go to leave for work yesterday and the truck wont crank. This is the third time this has happened in the last 6 mo. Replaced starter and flywheel 2 mo ago. I did what I did before in this situation, turn on key and jump the solenoid on the starter. Starts up I drive it to work shut it off try to start and it starts right up problem gone. Well this time I noticed that my ac compressor was not kicking in on the way to work. So I get there and shut it off try to start it up nothing no crank no clicking, but I have dash lights on and fuel pump runs. I end up starting it this way all day. I do landscaping and go from job to job all day. So now it wont start and no ac. My gf works with me and she drove her car so she was following me. After a couple jobs she tells me something is weird with my brake lights. She was right when you turn the key to on the brake lights come on when you hit the brake pedal they go off except the 3rd light works normal but its on a different circuit so not surprising.
    One other thing that is going on is a couple weeks ago I smelt a burning smell and my ac quit blowing. After fooling with the hi low switch on the panel off and low run the fan on high and medium and high shut off the fan. I believe this is unrelated to my problem. But who knows.
    what I have done,,, Thought for sure it was the ignition switch and it was late last night I had to get the part before they close so purchased one and half installed on the truck. Couldn't get the reverse tourqes loose in the column to install it completely. Tried it with a screw driver and everything is still the same. I was unable to plug in 2 of the things up at the key end. 1 was a small 3 plug wire with small wires the other was a piece f plastic that looks like it hooks on to something for positioning. Didn't think it would matter that may keep from cranking but it should have fixed the brake light problem. Reinstalled old switch to do some testing.
    Started at the top by the key tested pink wire I have power in try to test yellow wire coming out when I poke it, it cranks the truck with the key in the on position I don't even get to turn the key to the start position. I also tested the start relay wires and everything seems normal there except for my light is not very bright when I test the p/w signal wire telling it to crank. I have a mechanic bud coming over in a few to see what we can come up with.
    I am stumped what could be common between the no crank situation, the backwards brakelights, and ac compressor not kicking in. The relays for all three are in the same box but so is the fuel pump and probally the main relay if there is one. The fuel pump is working normal,
    Ok thanks for any help you can offer very much!!!
    Steve
     
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  2. tanman34

    tanman34 Member

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    Ok friend came over and even more confused weird reading and test results and cant change the ignition switch without a special reverse torque tool. For one screw. .He thinks something is back feeding some where. One thing we noticed in our testing is if you turn the hazards on and off you can get the starting lights on the dash to come on and sometimes you can get the fuel pump to run for a few seconds like you turned the key on. If you test the start relay with the relay out the lugs where it was plugged in seem normal. I am getting a start signal there but when you plug the relay in you loose the start signal. You can jump the out to starter lug, purple wire and it cranks the truck like it should. So the out side to starter I think is ok.
    We are stumped and not sure what the problem is.arrrg
     
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  3. dirtrider73068

    dirtrider73068 Moderator
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    Is there another relay like the horn relay thats the same swap it out see if it cranks with key, might be the relay is bad or burnt or shorted out.
     
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  4. tanman34

    tanman34 Member

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    yes we tried that nothing changed
     
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  5. leolkfrm

    leolkfrm Full Member

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    have you cleaned grounds? a lot of the newer stuff is controlled thru ground side....might try using a jumper from bat to firewall
     
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  6. tanman34

    tanman34 Member

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    yes cleaned both terminal that were not dirty just did it in case...no change. I will try running a ground to firewall. Anything is worth a try.
    Thanks for the input guys keep it coming!!!
     
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  7. MrMarty51

    MrMarty51 Full Member

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    "USUALLY" when weird things like what You are experiencing happens, it leads to bad ground.
    Make sure that all of the grounds are clean and tight, at the engine, between firewall and engine and also try jumping from the battery to the frame.
    Check the plug at that one relay. Be sure that there is no bad connections going on there.
     
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  8. tanman34

    tanman34 Member

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    Mr marty you are correct about this pointing towards a ground issue. I did as leo suggested and hooked my jumper cables from battery to firewall...no change. I will try one to the frame also.
    I have checked all the grounds I can find.
    1. Battery ground to front pass side of motor... two wires there
    2. Behind left headlight... 1 wire
    3. behind glove box.... 3 wires I think
    4. passenger side frame... two ground straps....the big one is hooked to the back of the head...the smaller one has never been hooked up since I had the truck. Its not very long to reach somewhere other than a manifold bolt. Where it hooks to the frame may could stand to be clean... wouldn't think so but sometimes you just don't know.
    I am going to work on it more this weekend for now, I have a toggle switch hooked to ground and the yellow out wire form the ignition to crank it. And I pulled my brake light relay out and using the taillights for brake light turning them on and off manually.
     
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  9. MrMarty51

    MrMarty51 Full Member

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    It might take a mirror and a flash light to see it. There is suppose to be a bolt into the back of the head on the passenger side, that is where that short grounding strap hooks to.
    It does sound like You have the bases covered.
    Try hooking a volt/ohm meter to the block then to the frame, see how much resistance there is between the two. Can also go from the block to the firewall.
     
  10. tanman34

    tanman34 Member

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    I am going to try some extra grounds.
    When I got this truck I bought it cash from a buy here pay here place. I didn't drive it a lot at first it was a nice truck and I got it to pull my boat. Everytime I let it sit for a few days the battery would be dead so after a new battery and cleaning everything and checking out what I could think of. I went up under the dash to see if there was something extra draining it. I spotted a little red light I reached up inside the dash and found a black unmarked box with wires and light burning. Asked some mechanics about it they didn't know thought maybe it was a tracking device. it had pos- neg wires and two black wires that run up my driverside post under the headliner. We cut it out and tried it without it ran fine till now. Has anyone seen one of these in their trucks???
    Also at that same time we found another small gray box about 2 in square with a little door on one that when you opened it there was a small circuit board card in it. Noone knew what it was so I removed the card. It has ran fine without it. It looked like it was all retaped where its wires are, so we thought it was part of the black box system. Has anyone seen one of these gray boxes???
     
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