I have a low voltage problem on my 1980 265 w/ rebuilt 1976 B21F engine. The battery reads 12.5 v in the car, and the alternator has no trouble charging the battery.

The cabin voltage is always low, though (as read through cig lighter port.) At best, it might reach 12 v when driving down the road with no electrical devices active. But with headlights and wipers on, it drops to below 11 v. The windshield wipers move much slower than in my 1985 245, and the headlights are dim. Always.

The car has a "new" rebuilt alternator, and a "new" rebuilt windshield wiper motor. The behavior has not changed regardless of these component replacements. (Wipers aren't any faster or slower with the new motor.)

When the engine is off and the key is turned to activate the accessories, the voltage reads back at around 10 v at the cig lighter port. At the same time, reading across the battery itself shows 12.5 v.

Anyone seen this one before?

...according to an old Clymer 240 Manual, begins at the smaller red wire running from the Battery + terminal to the small black junction box nearby, on the inner fender. From there, 4 wires lead to these points:

1) Ignition switch (Red in, Black out to fuses 1-2-3, Blue/Yel to 11-12-13)
2) Fuses 6 thru 10 (Red in to common left contacts)
3) Headlight flasher relay (Blue)
4) Headlight switch (Red)

Take the Battery Negative terminal off and carefully inspect the + terminal end of that small red "feed" wire for corrosion and broken strands. If OK, take the Junction Box cover off (pry out at the bottom and slide it UP), and compare voltages there. Chances are that's where it's dropping.

In any case, I'd take all 5 of those JB terminals off and on several times to burnish thru any corrosion. If interior voltage is still low, trace out items 1 and 2 above.
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Thanks for all the replies - I probed around with the meter and found that the voltage drop appeared at the fuse box. Cleaned some contacts on the PD near the battery and things are looking up! 12.5 v in the fuse box now with accessory on; around 13v when car is running. And the 14 v across the battery is good when car running (always was good.)

Are you having any problems with the car? Have you probed the voltage elsewhere (at the fuse box)? Have you probed the battery with the car running for 14v? The cig lighter may be giving you a bad reading. I've learned that 240 dash wiring may not always be "honest". :)

-Ryan
--
Athens, Ohio -- 1990 245, 125k, M47, E-codes -- 1991 745, 278k (girlfriend-mobile)

Check all your grounds.