Battery drain troubleshooting findings

[Michael F.]

Today I decided to look into a battery drain problem that's been with my car for two owners now for almost 20 years. The previous owner gave up and installed a quick disconnect on the battery, but I don't like using it as a crutch for a problem. So I dug in. Going fuse by fuse uncovered nothing. The drain was still there with all fuses pulled. About 560mA.

Disconnected the alternator as faulty diodes can cause drain - no change. Pulled the fusible link off the relay on the fenderwell, no change. Finally went under the car and checked out the starter wiring and noticed that it didn't look quite right. According to the schematic, there is supposed to be the battery cable and a feed to the main harness landed on the large solenoid terminal (B+). But mine had a black wire there as well. The wire appeared to be a factory type wire with a factory crimped large ring lug on it. The schematic shows a small black wire connected to ground at the starter, not the positive. This is the ground lead for the blower and wiper motors. Interesting.

It seems that someone in the past put the blower motor/wiper motor ground lead on the (B+) terminal instead of on the starter mounting bolt as it is supposed to be. Going back up top, if I disconnected the ground lead to the wiper motor and the drain disappeared. Sure enough, there was 12 volts on that ground wire!

I have no clue how this could have happened, as the starter has the correct part numbers and date code for my car. Perhaps it was rebuilt at some point. Anyway, for 20 years, the blower motor and wiper case were "live". I know for a fact the wipers worked because I tried them out before I bought the car. Didn't try the blower at the time though. I didn't try more than one speed or the washers.

With the black wire connected properly now, there is zero drain (except for the momentary clock coil) and everything works great.

Here's a pic of the correct location for the blower motor ground wire on a late '68. Hope this helps someone in the future.

[Rich G.]

Re: Battery drain troubleshooting findings

Congratulations! I love stuff like this. It proves there's a reason for every anomaly. I guess the cases of those accessories must be isolated from the chassis.

Rich

[Terry M.]

Re: Battery drain troubleshooting findings

Today I decided to look into a battery drain problem that's been with my car for two owners now for almost 20 years. The previous owner gave up and installed a quick disconnect on the battery, but I don't like using it as a crutch for a problem. So I dug in. Going fuse by fuse uncovered nothing. The drain was still there with all fuses pulled. About 560mA.

Disconnected the alternator as faulty diodes can cause drain - no change. Pulled the fusible link off the relay on the fenderwell, no change. Finally went under the car and checked out the starter wiring and noticed that it didn't look quite right. According to the schematic, there is supposed to be the battery cable and a feed to the main harness landed on the large solenoid terminal (B+). But mine had a black wire there as well. The wire appeared to be a factory type wire with a factory crimped large ring lug on it. The schematic shows a small black wire connected to ground at the starter, not the positive. This is the ground lead for the blower and wiper motors. Interesting.

It seems that someone in the past put the blower motor/wiper motor ground lead on the (B+) terminal instead of on the starter mounting bolt as it is supposed to be. Going back up top, if I disconnected the ground lead to the wiper motor and the drain disappeared. Sure enough, there was 12 volts on that ground wire!

I have no clue how this could have happened, as the starter has the correct part numbers and date code for my car. Perhaps it was rebuilt at some point. Anyway, for 20 years, the blower motor and wiper case were "live". I know for a fact the wipers worked because I tried them out before I bought the car. Didn't try the blower at the time though. I didn't try more than one speed or the washers.

With the black wire connected properly now, there is zero drain (except for the momentary clock coil) and everything works great.

Here's a pic of the correct location for the blower motor ground wire on a late '68. Hope this helps someone in the future.

Mike

Congratulations on a fine methodical job of troubleshooting. Placing the ground lead on the 12v starter stud is a not uncommon issue. We usually discover it because the wipers do not operate properly when the ground is connected to the positive voltage. I am surprised your wipers worked OK.

[Dan B.]

Re: Battery drain troubleshooting findings

Great post, I am sure a few people will owe you a thanks who have battery drain. Nice job of troubleshooting the problem to a successful conclusion, very satisfying. I am betting a few people will be checking their starter wiring now. Applies to C-2's also

[Leif A.]

Re: Battery drain troubleshooting findings

Yup, good stuff. Thanks for sharing...exactly what this forum is all about.

[Michael F.]

Re: Battery drain troubleshooting findings

Thanks! That's exactly why I joined NCRS and love this forum - to share what I know and to learn what I don't.

There was one other potential problem I found while troubleshooting that I didn't mention before because it wasn't causing me a problem - but it could have:

The courtesy light housings in a convertible are next to the kick panels, plus one in the rear area. I found that one of my courtesy lights was not seated in its bracket, leaving it free to dangle around. The problem is that the outer case of the bulb is somewhat exposed even when seated in its socket so it could easily swing up against the bracket (which is metal and tied to the chassis ground) and turn on the bulb.

My bracket was bent slightly which prevented the socket from seating all the way so it was an easy fix to bend it back into the correct shape and re-seat the socket.

So, if you're checking for battery drains, make sure the courtesy bulbs sockets are seated firmly in the bracket.

Also interesting is that the bracket in the rear storage area is nearly identical to the ones at the kickpanels except the mounting hole is different, and its mounted with a rubber isolator whereas the kickpanel brackets are screwed to the dash steel.