Electrical Questions

I'm looking for some advice to chase down some gremlins in my wiring. My fast and easy solution would be to buy a new harness and rewire it, but I'm really curious to know what the heck is going on. Any help would be appreciated.

CAR: 31 Chevy 5 window coupe, 327, TH400. wiring harness from early 70's Camaro.

I recently replaced the external voltage reg and 10 series alternator with an internally regulated 12si alt and replaced the battery at the same time. Old alt had a burnt diode and battery was only pushing 10 volts (although car started everytime.....). This was about three months ago. Main alt wire goes to the horn buss relay connector. Power wire to #2 term comes from main output terminal, sensor wire goes to harness.

I have never had an issue with the car starting - so I know it's charging ok.

Whenever the car goes to normal idle when I start it or when I come to a stop, the voltage gauge is around 13 volts. When I accelerate, always goes to 13 to 14 volts - headlights are bright, gauges are bright, all it well.

I've checked the main cables from the battery to the starter and from negative terminal to the engine ground (one of the engine / trans bolts)

However, most times when I'm driving and let off the gas, my volt gauge drops to about 8 volts, if lights are on - they dim, and my engine coolant temp gauge rises. If I go extended around town or on the highway, I can't keep accelerating, so my electric fan doesn't run long enough to keep it cool. If I give it some gas, the temp gauge drops immediately. I think the voltage drop is a direct correlation to the temp gauge - I figure with less volts, the sensor translates that to "hotter".

Can anyone offer any suggestions? My understanding is that I should not normally drop below 12 volts or so unless I've got pretty much everything turned on...or never


Thanks in advance,

Troy

 

Have you checked your grounds and make sure your engine block is grounded?

 

I agree 'sounds like a bad ground.That,s why the temp gauge is being affected.

 

Do you have a one-wire alternator? Most do not charge at idle.

Do you have a three-wire alternator? If so, the brown wire to the #1 terminal must be connected to either the GEN light or a resistor that runs to switched +12V. This signal is required for the SI-series to start charging.

 

Sounds like a ground problem to me too. Could be in the dash panel.

 

3 wire alt - it does charge and has the fusible link still - so it does charge - just erratically. Guess I'll spend the day tomorrow checking grounds....

 

I think joe is right. if exciter terminal doesn't get 12v it won't charge at engine rpm below 2000 [about]. running key on power to it will solve the problem but you will have to put a resistance in line. a diode or indicator bulb other wise alternator will back feed and engine won't turn off.

 

Went hunting for a ground strap - didn't find one - so I made one up, connected the engine to the frame and all my problems went away!! Problem was not charging related, it was the intermittent output.

Thanks all,

Troy