Back before I took my car apart, I had a lot of electrical problems. For example, when I would turn my headlights on, my turn signals would blink slower than with them off and the amp gauge would go up and down with each blink. MY headlights would also dim whenever I came up to a stop light or sign.

After removing the engine, I searched and searched for a possible cause. The only thing I found was a bolt on the rear passenger side of the intake manifold with a lot of rotted wires. There are four wires coming off of it and only one is still in good shape. The one wire left is the grounding wire that goes to the firewall behind the passenger side head.

My guess is that the other wires were for grounding something, but I can't figure out what. Does anyone know what these wires (pictured below) should hook up to on a 305 TPI engine? Thanks

 

The braided one is a ground strap that goes to the firewall somewhere to make sure there is a good ground path between the engine and body (there should be another ground wire between the battery negative terminal and the pass. side inner fender). Those are very common ground connection points on many many GM vehicles.

Now the other wires that are clearly WIRES, and not just a ground strap, are grounds to the ECM and possibly/probably gagues and other electrical things. GOTTA figure out where their matching wire is in the wiring harness and hook them back up. Yes, you can get some very odd behavior without good grounds. The problems you've described are CLASSIC bad-ground behavior.

Those ground wires on the back of the engine almost always get butchered and/or never hooked up again if the motor has ever been out of the car.

Also, the factory didn't originally ground them to that intake manifold bolt. They were retained by a bolt on the back of the cylinder head (that rusty bolt hole that's showing the impression of a star washer is probably one of those places). In fact, the TPI and TBI engines had grounds going to the back of BOTH cylinder heads (every one I've owned has, anyway). So clearly somebody was messing around with those grounds before you.

 

Your headlights and signals dimming is normal, most third gens do it, alot came with a85amp alternator. Those wires on the back of the manifold should be bolted to the back of the cylinder head. they are grounds for guages and sensors. the grounds for the headlights and signals are on the rad suppoort near the battery. Get a alternator for 89'88' car thet are rated for 105 amps, direct fit.

 

ha i had one of those mystery wiring jobs, my headlamps and tails would turn on when i hit my hatch button. crazy stuff lol

just get a wiring diagram, find the color and start searchin thats really gonna be your best bet

 

Thanks for all the info. I've been looking through wiring diagrams for a while, but have yet to get any clue as to what those wires are. The diagrams in my Chilton don't even show the grounds and they are also telling me that my car doesn't have an ignition coil . Anyone know of a place to get good diagrams of an 87 5.0 TPI and an 89 5.0 TPI engine wiring? Thanks