500ma parasitic battery drain - relay issues, ignition, or something else?

[kryptoniterazor]

Hello friends,
I just bought a wonderful little 1992 ranger custom. Runs and drives great so far - only problem I'm having is the battery ends up dead if I leave it parked more than 24 hours (and the armrests are falling off - nothing a little woodworking can't fix).

I did a quick current test with the multimeter, and it draws about 500mA with the key out of the ignition and the doors closed, lights off. (1.8A with the door open, light on). Oddly, nothing changes if I remove the "interior fuse panel" fuse in the power distribution box. However, if I remove the fuse for the EEC relay, draw drops to about 5mA. So I started poking around at the relays. The EEC relay (brown 4 pin one) appears to work fine - high current circuit is normally open, then closed when 12v is applied on the low side. Same for the fuel pump relay (green 4 pin). They click quite nicely. However, when I was removing them I noticed that the WOT cutout relay (black, 5 pin) clicked on and off when the wiring harness was jiggled, activating and deactivating some motor elsewhere (good thing I forgot to disconnect the battery first!). When I removed it I discovered that Pin 4 (normally ON, I think) had broken in two and part of it is presumably stuck in the harness (only got a look at it when I took it inside).

Looking at the schematic I don't really see how a broken WOT cutoff relay would cause a parasitic drain, but clearly it needs replacing anyway, so I'll do that. But given the EEC relay seems fine, where should I start looking next? The logical place seems to maybe be the ignition switch - perhaps it thinks the key is still in the switch and it keeps something hot that shouldn't be? Another possibility is a miswired harness that always powers the EEC relay, but I'd think the previous owner would've noticed that, and he said he never had issues with the battery draining except when he left the lights on once or twice.

Anyway, for now I'll keep disconnecting the battery when I park it but I'd love to be able to rely on it starting! Thanks in advance for your suggestions.

Attached is a diagram of the relays and locations.

EDIT- realize this should've gone in the electrical help section! Happy to delete and repost if that's preferred.

 

[Jim Oaks]

You have to leave the doors open and let the truck sit for a good hour to make sure it went in to battery saver mode before doing a test.

 

[kryptoniterazor]

Ah, good to know, thanks! I park in the city so I'll have to set aside an hour to babysit the truck and try it then.

 

[RonD]

I didn't think Rangers got a Battery Saver relay until 1995 when the GEM module was added?

So I don't think you need to wait

WOT(wide open throttle) relay is only used in Rangers with AC, and it is OFF all the time, except when your are driving with WOT and computer then activates that relay which cuts power to AC Clutch/Compressor

It uses a 5 pole relay instead of 4 pole, so 30 and 87A are connected when its off, that allows 12volt to flow to AC Clutch IF...........AC is switched on in the cab

WOT relay's coil should only have 12v with key on, EEC relay closed, computer Grounds WOT relay coil to activated it when it see TPS(throttle sensor) at WOT

A relay draws .5amps(500mA), so if WOT was shorted and had power 24/7 then that would be your drain

Engine Computer and radio both have KAP(keep alive power), computer uses it to "remember" control settings, Radio uses it for pre-sets and clock
This should only be a .03 to .04amp(30-40mA) draw, keyless entry adds a bit more, can be as high as .07amps

 

[adsm08]

Two things:

1) The doors should be left open, but you need to get the door ajar switches closed so the dome light doesn't add to your draw.

2) on a 92 everything should shut down pretty quick. Even a newer vehicle should be powered down in 20 to 30 minutes.


On something that old the alternator is one of the few things that can cause a draw big enough to kill the battery over-night.

 

[a31ford]

I agree with Adsm08, a bad diode in the alternator will cause a slow drain that will kill a battery overnight. as a fast test, close the doors with the window down, and the hood open. disconnect ALL the wires to the alternator (CAREFUL for the main wire as it is still live !!) if the main wire disconnect removes the drain, then the alternator has a leaky power diode, if the other plug removes the drain, then the regulator is bad.