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 when the fan and headlights were on, volgage dropped by 2. This drop did not occur on the data logging trips I took right after the fans were installed.

I suspect my old alternator did not like the additional power draw and is going bad. My alternator is a 70 amp version. I wired the fan relays directly to the battery, per the instructions in the relay kit (got the Jegs dual fan kit).

Anyone with similar experiences? Also, is there a better place than the battery to wire the relays? I thought I saw on a post where some cars originally had the fans wired to the positive post on the starter.

 

check the voltage right at the alternator output stud
to see if the voltage drops under load there-if it drops
more than a few 10ths of a volt with fans,lights, etc
on,alternator is faulty-usually a bad connection where
the crimped on ring terminals from the stator windings
connect to the rectifier-soldering the ring terminals
fixes the problem,could be bad diodes or worn brushes
too.If alt voltage stays above 13.5v under load,probably
a wiring problem. I have the original 85a alt on my '82
(my car had rear defog) and it has no trouble keeping
up with the accesories on my car:A/C,big stereo,aux.
driving lights,oil+tranny cooler fans etc.Did have to
fix the stator connections on mine though

 

I'll try that. I wouldn't think I need much alternator with no A/C and no major power draws from original except the fans.

 

Just for kicks, i hooked a spare dual fan setup from
my parts stash up to an ammeter and test ran it to
find out the current draw-each fan pulled 7 1/2 amps
when fed with 14.2v,15amps together. even the
smallest 3rd gen alternator(42a on certain early
"stripper"models)should easily power these fans with
power to spare