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Discussion Starter · #1 · (Edited)
This is on the Mutt, the 1989/1993 truck. Very low amp draw, takes 2-3 months to make battery tired but still start truck. I hooked a test light up between negative battery post and negative cable and it lights up, and is pulsatile. Pulses on and off rapidly, every 1/2 second. So I started pulling fuses and noted the CD player in the radio was making pulsing noises and the cargo light pulses as well when I turn it on. It only stops when I pull fuse 15- controls map light, underhood light, cargo light, power window switch and other stuff. I disconnected the main light switch, cargo light harness, power window switch, glovebox switch, ignition switches (everything on column- when I did the this the key in buzzer stated pulsing noise wise), headlight switch, the entire harness to the speakers and cargo light and changed radios out and the damn thing still pulses unless I pull fuse 10 15. Figuring a ground was bad, I cleaned the rad support ground and re-did the ground for the radio near the cargo light switch. I also disconnected the ECM thinking that as a possibility, but still pulsing.

This makes no sense- only thing I can think of is 2 hot but low amp wires have to be touching? Mu Fluke 325 amp meter isnt even registering amps between neg post and cable. Just the test light.
Any chance its a bad battery? its an older optima, and I actually took it out of my 92 last year bc it was weak. But it took a charge saturday.
 

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on a 1993 fuse # 10 is for the wipers
 

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fuse #15 is mostly radio memory and dome lights
 

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Discussion Starter · #4 ·
doggone, thats a typo on my part. I pulled fuse 15 to stop the surging in the STOCK cd player/radios and thru the cargo light switch
 

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If you disconnected everything listed on the circuit and it's still pulsing, you have something added to the circuit or something not listed. Pulsing signals makes me think fuel level sender. Are there any aftermarket items? An alarm?
 

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Discussion Starter · #6 ·
Its totally stock. i'll be disconnecting the plow wiring soon but thats not even plugged into the plow side yet. I was certain it was going to be the radio but have tried 2 different ones with same results.
 

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well radios do have channel memory and are powered by 3 different fuses # 15 full power[memory] # 8 key-on power and # 14 H/L illumination power

the head light or ignition switch could be leaking

the PCM also has memory power
 

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also all dome/cargo lights have full power till grounded
 

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Discussion Starter · #9 ·
I disconnected the headlight switch, all steering column wires including ignition switch and the connectors to the dome/speakers/cargo light and the damn thing still was pulsing. it makes no sense for anything else than a backfeed- I have a couple more grounds to check I think.
 

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Also try unplugging the headlight/key in/seatbelt buzzer.
 

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trailer connector , emergency battery's charge wire ? ( if its got one )snow plow electric valve coil energized ? alternator field hot all the time ? ( install external old style regulator ) ..
 

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The pulsing is the issue. Seems to me that something is drawing down voltage whatever you see the pulse in (dome, headlights, radio etc) and then it stops, and the cycle repeats. . Have you pulled both flasher units? I can't understand anything other than a flasher or something with a capacitor is causing the problem. Just for giggles, I'd also disconnect the VR and the alternator output wire.
 

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I would put the fuse back in then unhook things on that circuit one at a time, starting with flashers & power window switch.

Bucky
 

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disco the alt field wires , remember the pcm controlls the ground side of the field , so test it not just the "hot" side .... pulse says to me maybe something like a bad condenser , or what ever electronic gismo has taken their place ...
 

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Discussion Starter · #16 ·
I had maybe 20 minutes to work on it today. disconnected the buzzer and wiper modules. Replaced battery since I knew it was weak. No change.
Fooled around with switches since fuze 15 does power mirrors too. Pressed power door lock and pulsing stops and it glows continuously.
I agree disconnecting alternator is next step, then door locks
 

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well radios do have channel memory and are powered by 3 different fuses # 15 full power[memory] # 8 key-on power and # 14 H/L illumination power

the head light or ignition switch could be leaking

the PCM also has memory power
Most radio memories are powered by less than 1 volt (.05v). The battery would have to be pretty old to really be affected by stereo memory. JMO.
 

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I had maybe 20 minutes to work on it today. disconnected the buzzer and wiper modules. Replaced battery since I knew it was weak. No change.
Fooled around with switches since fuze 15 does power mirrors too. Pressed power door lock and pulsing stops and it glows continuously.
I agree disconnecting alternator is next step, then door locks

pull fuse # 12 , its a 30 amp circuit breaker and see what happens
 

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Discussion Starter · #19 ·
I had 5 minutes today to mess with it. Unplugged the 89 plow wiring harness that was only hooked into the head lights and NO MORE DRAW. I am concluding it was the 35 yr or more plow wiring harness. I plowed with it last night- its awesome
 

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I had 5 minutes today to mess with it. Unplugged the 89 plow wiring harness that was only hooked into the head lights and NO MORE DRAW. I am concluding it was the 35 yr or more plow wiring harness. I plowed with it last night- its awesome
WOOHOO!
 
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