When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
heres a mystery. In short, I installed a dash cam with a relay to control the lighter and dash cam. and now I’m seeing .05-1.0V. On the SWITCHED circuit with ignition off.
I followed this old RF thread. Everything works as it should. The dash cam and lighter circuit switches on with the key. Every ground is shared.
below is a picture because I can’t believe it myself and I do know how to read a meter. It reads clear 12V on normal circuits. Ignition is off and probes are at the switched lighter. The volts vary between.04-1.0 pretty quickly. More details below.
red tape holds the rusty antenna cable firm.
any idea where to look? Some magic physics book perhaps. What could be a source of 1v in a 12v ground truck? I’ll try disconnecting stuff one at a time. Maybe it’s coming OUT of the cam? Will check.
Cigar lighter is not on a switched outlet, has full time 12v
So the full time 12v wire is now going to the relay's, pin 30 or 87
And the 12v OUT, pin 30 or 87 goes to cigar lighter and camera
And you have picked a Key on 12volt source, which one?
There can be phantom voltage from other devices on a 12volt switched wire, from capacitors mostly
Also from the ground side, remember you are reading a voltage difference between the two Meter Probes
Pull battery positive cable and see what you read, and if 0.4v slowly goes away
Thanks a million for the ideas. I started the day checking again and The relay is ground, radio switched and hot is coming from lighter on the 20a fuse. I double quadruple checked.
the lighter is on the relay dash cam circuit now, so it’s switched. Supposedly.
Here’s next steps. I found a parasitic draw of 150-200ma and it goes away on the fuse 25 instrument cluster / GEM fuse.
To my knowledge, I didn’t touch that circuit except maybe it’s actually the radio clock? The radio clock black yellow as I understood is the switch source.
im about to undo all this work. Backspace or whiteout depending on your age.
1999 Ranger has a GEM(module) behind the radio, it is the Body Computer, it controls interior lights, wipers, pretty much anything electric in the cab
It has a Timer circuit, this timer is activated when key is off/out and all doors are closed, timer takes 20 to 40minutes to count down, it then cuts power to most circuits in the cab, using the Battery Saver Relay
So to test amp draw you have to hook up amp meter then wait until timer shuts things off and GEM itself "goes to sleep"
Fuse 25 in cab fuse box should have full time power for GEM, cluster, AND PATS(passive anti-theft system), might see amps go up and down as THEFT LIGHT on the dash goes on and off every 5 to 10 seconds, as a warning to theives
Fuse 28 is the Radio MUTE while starting, fuse 28 only has 12v when key is activating stater motor, and that MUTES the audio out on the radio
Fuse 29 is the full time power for radio, holds Clock and Pre-sets memory
Fuse 20 is the Key On power for the radio, the yellow/black wire, yes this could be used for a relay's coil, pins 85 or 86
When pin 85 has 12v and pin 86 is grounded then Relay activates and connects pins 30 and 87
85 and 86 have no polarity
Either can be the ground or 12v, but it needs both
Does this make sense? I pulled all the fuses to identify the draw. One at a time.
pulled 25, Instrument GEM. it dropped to 0.01A perfect. I reinstalled it.
pulled 26. This one is connected to lots of stuff. Battery saver relay, shift relay, Interior lamp relay , power window relay, electronic shift control module ,Dom lamp and of course GEM also.
I reinstalled it and the draw is back to almost nothing 0.07. Still high I guess but better or just not precise at the 10a scale.
