Grrrrounds

[pullmyefinger]

85 GMC S15, 2.8, 4 speed, 6 cyl manual tranny.

Gauges are going crazy. I was reading in another forum about ground straps causing havoc with electrical systems and that is what it is doing.

Specifically:

lights on the dash panel and headlights flicker on and off now.

recently installed a relay with a temperature sensor connected to an electric fan. I was told the engine wasn't getting up to operating temperature and that is not good. gas mileage stinks for one thing, and it's a stick shift that should be getting 15+ around town according to the EPA estimates.

fan used to run constantly, now it is supposed to run only when the engine temp sensor tells it to.

now, alternator gauge starts ok and gives me 15-16 volts, oil pressure gauge is ok and temp gauge is ok when in fast idle for 4 minutes (even in the middle of august it goes into fast ide or it runs like crap).

Once I put it in gear the gauges go stupid, even though the alternator was rebuilt a month ago and puts out 14.7v on the charging line. Belts are fine and do not slip or squeal. Battery is ok at about 12.6v at rest. We fixed a radiator leak recently too.

The alternator gauge starts to drop down when I put the truck in reverse or any other gear. The lower the alternator gauge goes the higher the engine temp gauge goes forcing me to stop and shut it off. I turn it back on almost immediately and the gauges go back to normal, then the same old crap starts. The relay/temp sensor/electric fan stuff comes on and cools the engine down. This all happens within 5 miles driving. It used to also make the radio/cd player beep and reset along with the fasten seat belts light coming on, but the truck still ran fine. Oil is clear, recently changed and does not look like a milkshake.

I cleaned, wire brushed and put dielectric grease on all the grounds I know of, even the dash gauge ground by the emergency brake. No difference.

There are two wires bolted to what seems to be the bell housing bolt that are fried.

IS THIS AN ENGINE GROUND?? There is another ground that connects to the firewall in the middle that grounds the blower motor and the relay and that Seems OK. We added an extra ground to the frame for the headlights and the battery; that one might need cleaned up again even though it seems tight.

We also removed the dash panel and an electrician checked all the copper tracings and said they were ok.

What I want to know is Where are all the grounds supposed to be on this vehicle? Where do they connect, starting and ending? What else might be causing this mess?? I don't know enough to do everything and am getting tired of not being able to drive the truck for fear of the wiring harness burning up and God knows what else... Any help would be appreciated, even links to other sources cuz my Haynes manual probably isn't specific enough.

[hatzie]

The engine is grounded by the main battery cable on the alternator bracket. Make sure the bracket to the block is making good contact and the star washers are making good contact from the cable to the bracket.

You should also have at least one small ground wire from the battery terminal to the radiator support or fender and one engine-to-cab/body ground strap. I'm not sure exactly where these are in 1985 and the factory diagrams don't provide that level of detail. Your "Fried wires" on the bellhousing are probably the body ground. I'd be willing to bet that they are braided ground straps that corroded off in the last 29-30 years. Replace them with new braided copper straps and coat them with Fluid Film or the like to kill any corrosion.

You may want to check the ground buss bar under the dash. It's a big chunk of stamped copper, brass, or copper plated steel sheet metal with six male 1/4" disconnects that are a part of the stamping. In stock dress there should only be one ground wire attached. The Buss Bar should be firmly attached to and thus grounded to the body. If there's corrosion on the attaching hardware or missing the star washer you'll have dash ground issues.

I added braided ground straps from the block to the frame near the motor mount on both sides of my diesels and from the top bell-housing bolts to the cab. I also added a ground wire from the frame to the bed behind both taillights.

I've seen HAM Radio guys add ground straps along vehicle hood hinges, from the radiator support to the fenders, and fenders to the cab to cut down on noise... Not sure how effective or even needed these are. They might cut down on electrolytic corrosion at body bolts etc by electrically tying the whole sheet metal and frame structure together... Dunno.

[KQQL IT]

Police interceptor Vics have ground straps in several places.
That being said loose grounds will cause havoc

[pullmyefinger]

Thank you for the info. The more I learn I realize the less I know. Never knew there was a buss bar under the dash so I will have to check that out. The bell housing wire insulation burned off one day and the corrosion didn't help it either. We added another ground to the frame at one time, but I thought I remembered a separate ground/small wire going from the negative terminal to somewhere else (along with the one to the alternator bracket). I changed the ground wire and/or connector a year ago and totally forgot about that extra wire. Thank you so much, I will let you know what happens!

[pullmyefinger]

Originally Posted by hatzie

The engine is grounded by the main battery cable on the alternator bracket. Make sure the bracket to the block is making good contact and the star washers are making good contact from the cable to the bracket.

You should also have at least one small ground wire from the battery terminal to the radiator support or fender and one engine-to-cab/body ground strap. I'm not sure exactly where these are in 1985 and the factory diagrams don't provide that level of detail. Your "Fried wires" on the bellhousing are probably the body ground. I'd be willing to bet that they are braided ground straps that corroded off in the last 29-30 years. Replace them with new braided copper straps and coat them with Fluid Film or the like to kill any corrosion.

You may want to check the ground buss bar under the dash. It's a big chunk of stamped copper, brass, or copper plated steel sheet metal with six male 1/4" disconnects that are a part of the stamping. In stock dress there should only be one ground wire attached. The Buss Bar should be firmly attached to and thus grounded to the body. If there's corrosion on the attaching hardware or missing the star washer you'll have dash ground issues.

I added braided ground straps from the block to the frame near the motor mount on both sides of my diesels and from the top bell-housing bolts to the cab. I also added a ground wire from the frame to the bed behind both taillights.

I've seen HAM Radio guys add ground straps along vehicle hood hinges, from the radiator support to the fenders, and fenders to the cab to cut down on noise... Not sure how effective or even needed these are. They might cut down on electrolytic corrosion at body bolts etc by electrically tying the whole sheet metal and frame structure together... Dunno.

***********************

Good, and thank you for the help. I will look for that chunk of metal today. Will also go get another ground strap cuz my mechanic and electrician both said that GM recommends grounding the tranny. Two times something smoked under the hood, and we added an extra ground or two. I hope one or both of these solves the problem. I am not going to drive the thing until I do this cuz if something smokes the harness and I could have fixed it first I will be pissed at me~