98 Tahoe... Power to the ground

I'm just looking for some ideas here. Even if they are the same ones I'm thinking. I've got a 98 tahoe LT 4x4, 5.7lt. Long story short the thing is running out of time due to Electro magnetic interferance. If I hook my test light up to the ground on the battery and touch it to anything metal on the engine the light will come on. This will happen only when the underhood fuse box power cable is connected to the battery(the cable is good). No fuses are blown because of this. I've taken the wiring apart from the computer to the engine sensors and can't find any bad wires or wires melted together.

I'm just looking for some ideas here. Even if they are the same ones I'm thinking. I've got a 98 tahoe LT 4x4, 5.7lt. Long story short the thing is running out of time due to Electro magnetic interferance. If I hook my test light up to the ground on the battery and touch it to anything metal on the engine the light will come on. This will happen only when the underhood fuse box power cable is connected to the battery(the cable is good). No fuses are blown because of this. I've taken the wiring apart from the computer to the engine sensors and can't find any bad wires or wires melted together.


First buy a volt-ohm meter...learn how to use it properly.

then remove the spark plug wires one at a time and inspect for damage and measure the resistance. with an open wire or a wire that has very high resistance you will get this interference ...usually the radio reception on AM gets poor...

the new wires must be around the resistance of the OEM spec. this is to ensure that the impedence is close to what is required to provide the correct spark to the plugs..

the spark plugs if cracked could also create this/as well as a bad cap/rotor..poor distributor ground due to corrosion..coil/connections etc...

always use silicone dielectric grease on the plug wire boot ends . this prevents water from cooking the terminations at the connector to cap/SPARK plug.....

Does the eng need to be running? Will it do this with the key off, or does the key need to be in the "run" position? Maybe check all your chassis grounds and make sure their all ok.

all this happens with the key in the off position... Doing a little more looking around and this is what I've found. My test light will come on when I touch anything metal on the truck and connected to the neg post of batt. checked and cleaned all grounds. Ok in the fuse box under the hood there is a large red 50 amp fuse labeled Batt, if I pull this fuse the light stops coming on. The cable from the battery powers one side of the row of large fuses in the fusebox and they run into some larger red wires. I been looking in my haynes book and on the autozone wireing diag and can't find where this wire off the batt fuse goes.

My '98 factory manual shows this wire gong to the I/P fuse block to power the "stop-haz", "pwr accy" c/b & "t-case" fuses. Also goes to the "starter relay" in the underhood box.

Just keeps getting crazier... Got the idea to pull the radio fuses and after doing that my test light would just barely come on for a split sec when you touched the alternator housing, couldn't get it to come on when I would touch the body of the truck (keep in mind that I've got the ground grounded to the neg on the batt and touching pos to anything metal and getting a light.) So I decided to pull the radio and now when i touch metal the light shines bright. I put my meter on the neg and touched the body of the truck with the pos and I'm getting a 12 volt reading.

One of your main ground wires has to be off. It is the only thing that can do that.. Does your battery go dead overnight? if no, then for sure it is a bad engine ground. you can test this by using booster cables connect one clamp to the engine then the other side to the battery negative, you will only be using one side of the cables. then redo the test light test. If that makes it good then replace or rerun a good size wire from an engine bolt to the battery negative.. I have seen that very problem cause repeated wheel bearing failures and shifter cables to sieze and other problems. the electricity will find a way through somewhere and arc weld parts together in the process.

Thanks guy this problem has been solved with my grounding problem. I'm going to start another thread with my origianl problem that got me here.

Thanks guy this problem has been solved with my grounding problem. I'm going to start another thread with my origianl problem that got me here.


Glad you got it fixed, but, I'm sure many of us would like to know what fixed it!!!!

It was a battery ground problem... It was not making good connection probably caused by me when I took everything off the front of the motor when i pulled the timing cover.