My rewiring project has shown that proper grounding on a fiberglass car is difficult and important. What are the basics of getting my new wiring harness's grounded? The old system was a diaster. What should be done to simplify this? TIA

Rick

 

Not sure I understand your question. What is the old system and why do you say it was a disaster?

Good grounds need to have clean contact with metalic parts that are ultimately connected to the negative terminal on your battery.

 

OK, on any car the circuits run from the body frame, in our case called the bird cage, as it's the steel part of the body, which is connected, supposedly through about 6 bolts, from the steel parts to the frame....but with rust/etc, you can get loousey connections...theoretically.....never seen one, don't mean it can't happen....

now, the battery connects the negative directly to the frame under the battery box....and then from the frame under in a NO SEEUM spot under the pass side engine mount....another short cable, SO the engine is presumed electrically to the frame, and therefore the battery....
of course the battery + term goes to the starter solenoid stud, and the wiring harness....

BUT in this course of things, you gotta clean hell out of the bolts/steel/copper terminals/ star washers to make damn sure everybody is happy......it was one of the first things I did back in '95-96 when I bought my car...just did it ersatz, PM,....
then I covered the bolts/connections with RTV silicone rubber, which is a great adhesive and weather proofing compound....IT wins, not the water/corrosion....

now in the body/pass compartment under the dash there is only one ground point I"m familiar with, that is up under the light switch area on the side above the air vent/kickplate area.....black wire. about 10 ga....

when I rewired my car, I split the grounds off to the other side of the car, as I waanted department of redundancy department....

yeh, you can tell, I"m an old electrical guy from way back when......

GENE

 

I don't know where every ground is located but I do know you will need a good ground between the engine and frame. Use a battery size cable - #2 to #0 wire. And checking resistance with an multimeter should really be less than 1 ohm. Anything less than 5 ohms would be acceptable but only dirty contact surfaces of cable (and multimeter probes) will prevent less than 1 ohm. My '74 has a battery size cable from metal of the motor mount on pass side of frame that I attached to the lower bolt hole of the fuel pump casting (wanted to plug that hole anyways).

Without a good continuity between block and frame all kinds of crazy things can happen. Most likely current from block will have to travel through u-joint bearings to the frame and this can produce different circuit voltages alternating with the speed of the driveshaft. But maybe you what your lights to turn into strobes at high speeds? Have also heard of the coil to distributor wire catching on fire when it becomes the ground path from the firewall plug - instrument panel power.
Hope this helps. cardo0