1999 Tahoe Electrical Problem, Won't Start

This particular problem is going to make me get a new truck, I think. Here is the problem. When I try to start the truck the starter seems like its not getting electricity. The headlights come on, the radio comes on, and everything else electrical seems to be funtioning, but the truck does not start. I have changed the starter solenoid and the ground going to the starter. I thought I had the problem licked, but then it started happening again. 1 out of 10 times the truck will start as normal, and if it doesn't I have to send someone under the truck with a piece of wire to jump the starter and then it will be fine and run until I shut it off. Sometimes I can start the truck right up again, but most of the time I have to send someone back underneath to get it going again.

I read here that it might be the starter relay under the hood, but I'm not sure where to look, and after looking on gmpartsdirect.com I can't find a starter relay part so I'm not sure where to go from there.

The other thing I kind of suspect is the dome overide button by the dash dimmer switch. It sounds crazy, and I can't confirm it, but a while ago I was convinced that the dome overide was shorting and causing my battery to go dead. Then it stopped and I forgot about it for a while, and I'm not a 100% there was a problem with the switch anyhow because it was intermitant.

The other strang thing that is happening just recently that makes me think it something electrical in the dash is the Brake and ABS warning lights on the dash started flickering out of the blue. They come on and off at the same time at random, not when hitting bumps or anything.

Any ideas before I take it to the electrical specialists Friday, and spend a fortune?

Not sure if there is a relay but when it does not start you must trace back the voltage from the ign switch thru the trans range switch to the starter, possible bad ign switch, or relay if there is one, or a bad range switch. You may need a wiring diagram for this.

ok, here is how the startng circuit runs. Starts from the IGN A #6(40 amp) fuse, from there goes out as two leads, one lead goes to the starter relay (in the underhood fuse block), the other goes to the ignition switch. Out of the ignition switch the circuit goes to the "crank" 10 amp fuse (#8 in the dash fuse panel). Out of the crank fuse to the transmission range switch (on the side of the transmission), then that circuit energizes the starter relay. When the starter relay is energized, it makes the first circuit that went directly to the relay (from the IGN A fuse), continue to the small terminal on the starter. Now, here is an easy was to help break this system to diagnose. Using a test light, when the starter won't start, see if the test light comes on brightly at the crank fuse in the dash fuse panel. If it lights normally, the ignition switch should be ok. If dim or not at all, the ignition switch might be bad, or a connection at the ignition switch is poor. If all is ok up to now, remove the starter relay. Again, with the starter not working, use the test light to see if there is power on two legs of the fuse block where the relay is located. If you hit all four with a test light, nothing will happen, but you must have power on two of the legs when the ignition switch is in the crank position. If you only have power on one, you need to check the transmission range switch or connection at the switch for a problem. If all of up to here, swap the relay with another relay, just match the number on top with one like the DRL or A/C or Headlamp relay (basically something that works you know the relay is good). If everything checks out up to here, you either have a bad connection at the starter, battery, or you might just have a bad starter. But given the fact you can "jump" the starter using a wire would tell me the connections at the battery and the starter are ok. Hope this is not too confusing, and helps. I can email you a picture of the schematic if you want to post your email address. But I tried to describe the circuit as best a possible.

Klinn, nice job

Just today an intermittent problem with my positive battery post connection caused similar problems. There are two connectors on my positive battery post. The post screw was tight, but green crud had developed under the connection which supplied the battery voltage to the main fuse block. So, I could start the motor, and sometimes it would run fine, but started cutting out whenever I would turn on any kind of load that would drop the voltage across the battery terminal with the crud - this dropped the ignition/ecm voltage also. Made for some strange symptoms. I was able to create the problem by wiggling the inner connector on the post with the motor running (and in gear/emerg brake on). If I tried it in neutral, the brake in the connection was too short to cause motor shut down. This icon is appropriate for me on this one: :banghead:

Well, I found the problem and its a doozie. It turns out there is a problem in the wiring harness somewhere and when the truck is warm and I try and start it, for some reason the signal does not get to the starter relay. So my options are, 1.) bypass the neutral switch, which I really don't want to do because of resale (You could ingage the starter with the truck in gear.) Or 2.) replace the wiring harness, which would be beyond my capabilities and expensive.

Just for grins, replace the "IGN A" fuse #6 40a in the underhood fuse-relay center and the "CRANK" fuse # 8 10a in the instrument panel fuse block. Let us know....Steve

GM has a lot of problems with the neutral switch. In fact, they can overheat and cause the two connectors to melt to it, and you cannot remove the connectors. The fix is obvious, replace the neutral switch and connectors. Are you sure it's in the harness, not in the switch?