jim morehouse

I got back from my vacation in AZ to find the battery on my '88 stone dead..again. I had been chasing a 135ma current drain before I left and hadn't had a chance to use some of the techniques posted in a previous thread so I wasn't surprised..BUT it's driving time now and I really didn't want to tear things up to find it.

I found what I think is a great alternative that will let me take my car on trips this summer w/o worrying about the battery. Intellitec makes a 100amp, magnetically latching relay (intended to switch batteries in RV's) for about $40 that's small enough I could mount it inside the battery compartment. Here's the site:
http://www.intellitec.com/pdfs/BATTERY_web/bd.htm

OPERATION:momentarily apply batt+ and batt - across the coil and the relay 'makes'..remove the voltage to the coil and the relay stays 'made' . Apply the voltage to the coil in the opposite direction and the relay releases and stays released when you remove the coil voltage. So no current drain thru the coil.

I use the relay to switch the connection between battery - and chassis ground. I ran wires from the battery/relay to a DPDT (double pole, double throw) momentary switch I mounted in the drivers parcel tray along w an LED that lights when the battery is connected to ground. I also put in two sockets, one connected to chassis ground and the other to battery - so that I can more easily measure current drain when I go back to trouble shoot this problem. (one of the things that came out in the previous thread was that dis-connecting the battery from ground to attach a current meter can re-set possible culprits, masking their drain and that you had to establish the meter connection first and then disconnect the battery from the chassis). I can just connect the meter, flip the switch, and read drain..no 'screw/un-screw' the ground connection.

It does mean that I "re-set" the LH control unit but it hasn't been an issue for me..the car starts and runs fine. I didn't want to put one of those big 'knife' switches in the back since I'd have to open the hatch and disconnect it. This way, from the drivers seat, I just momentarily press a switch, the LED goes out, and I know my battery won't run down. Get in, flip it, the LED comes on, and go. I may leave it in even after I chase down the current drain, just for insurance. I'd want to route the wires under the rear seat instead of between it and the quarter panel to hide the wires a bit more, but other than that, it doesn't look too bad.

Just thought I'd pass this on in case someone else was going crazy w their battery running down.

Jim

928FIXER

Looks like an old Ford starter relay.I'd be a little scared of the low amp rating on this switch.Takes a lot more than 100 amps to get a 928 starter motor to turn over...more like 250 amps while cranking

jim morehouse

Fixer,
the 100 amp rating is continuous. The max current is 500Amp for 30 sec so starting shouldn't be a problem.

Jim

LarryM

Jim,
Sounds good,,, and if the switch is hidden it can help in theft deterrence, and or Help keep your 928 Your 928.
Just a suggestion, when your meter showed the 135ma did you start pulling fuses/relays 1 at a time until it went away? That's how I found my last one. you probably did, I just wanted to offer what helped my in the past.
Good luck

Ron_H

I have an elusive gremlin draining my battery also. I have searched and searched for it over the past 1 1/2 years, but to no avail. I did the "multimeter/pull fuses" exercise about six or ten or fifteen times so far. Each time I found errant rellays which of course were replaced with new ones. Then I parked he car and went off whistling "I'm a happy camper", only to return the next morning to find a dead battery. The gremlin seems to be alive and roaming around from relay to relay. (Must be Karma or something.) Next step will be to completely clean the fuse/relay panel in the footwell per Sharkskin's preceedure. If that doesn't kill it, it's time to tear off the pod/dash and search for it wire by wire. That has been done once already, but it wasn't killed even after finding and replacing several clustered burned wires.

This switch sounds like a viable alternative. The only trivial annoyance is the need for re-setting the radio stations every time I start the car.

Thanks for posting ths information. I had hoped to find this gremlin before leaving for Pennsylvania, but I doubt that will happen. The switch will allow me to deal with the gremlin later, as you are doing with yours.

jim morehouse

Ron,
did you follow the earlier thread on hunting for the battery drain? I can't remember who posted originally but there were some good ideas in there and especially to connect the meter before disconnecting the battery ground.

Your radio likely has two different 12v connections, one always on (to hold the presets) and one switched to provide the higher power outputs. You could easily rig a small external battery to the always on lead to hold your stations.

Jim

Ron_H

Jim:
Yes I did. In fact it was Dave who first told me about the folly of disconnecting the battery ground strap before using the meter. I keep some alligator clips handy to use with the meter and attach them to the strap before it is removed.

I am about to install a new radio and will point this situation out to the shop.

Thanks.