I have an '82 that I converted from the original mechanical fan to dual electric fans from a '91. Other than one fan motor being bad, the conversion seems fine. However, I recently noted while data logging that voltage to the fuel pump and battery dropped when the fan (only one - haven't needed to replace the bad motor yet) comes on. Voltage dropped one volt at the fuel pump and battery when the fan came on and 2 volts when I turned the headlights on. Several times, the battery voltage was below 12. This drop occured whether at idle or driving down the road.

I have 3.73s in the back, so my RPM tends to be higher than what you would normally see. I wouldn't expect to have a problem driving down the road. I don't remember noticing this drop right after the fans were installed.

I suspect my old alternator did not like the additional power draw and is going bad. The battery is less than a year old. My alternator is a 70 amp version. I see a 108A alternator listed for 85-86 TPI cars. Is it the same physical size (i.e., will it bolt on)?

I wired the fan relays directly to the battery, per the instructions in the relay kit (got the Jegs dual fan kit). Is there a better place to hook into the power on a third gen? I know on older cars with an external voltage regulator, it is best to pull power from the bus bar located on the regulator since this is where the voltage sensing wire from the alternator is attached.

 

I would check the voltage right ON the battery posts (not the clamps) when your datalogger shows low voltage. You could just have a connection problem somewhere in the cabelage.

IIRC, all thirdgens use the same 70-amp alternator, regardless of fueling system. I haven't seen a stock bigger amp on our cars (it could be an option but certainly wasn't on all TPI cars). I sure have the regular 70-amp alternator on my TPI engine.

Hope this helps.
Lou