Electrical Issues

[85MudMonster]

I'm having some electrical issues on the CRTSY LMPS circuit which happens to control Dash Lights and Marker lights as well as Tail lights. What happens is after I turn on the lights about 3-4 minutes later it will pop that fuse no matter what fuse I put in there, it popped a 30Amper so I know that at some point it is pulling more than 30Amps across that circuit. After it pops a fuse if you shut the lights back off and replace the fuse it will pop instantly then, if you leave it be for a few hours and come back it will do this all over again. So I'm not sure where to start in my troubleshooting process. Electronics are my specialty but, the fact that it waits a good 4 minutes the first time before popping the fuse has me baffled. Any suggestions as to where to start my troubleshooting process? I was thinking about getting an Ampmeter and seeing just how much current that circuit is drawing...Any help with this is appreciated.

Thank you.
Dan

[Captkaos]

Sounds like you got something wired incorrectly.  Is there an aftermarket radio in it?  Reason I ask is because mine was doing that same thing and it would blow the fuse...  The previous owner wired a power wire into the ground on mine..  There wasn't a delay though.  You are just going to have to start tracing wires.

[Fordeatinz71]

wow, this is a bad circuit to have a fault in...namely because it has so many things running through it.  it could be a bad printed circuit, or possibly even a bad headlight switch. 

one method of finding shorts is to remove the fuse, connect a test light to the fuse terminal (there should be no voltage in the circuit), try moving around the wiring harness, see if the test light lights up.  if it does, then just keep moving it around until you are able to narrow down the exact part where the insulation is rubbed through...

[DnStClr]

It would be nice to see if there's a relay in that light system. A relay is used to insure that a switch doesn't get overloaded. The relay can take higher current. So if the relay fails, the switch will overload and blow the fuse. You'd have to put a test meter or light on the relay to see if it opens up after a few minutes. It's called "dropping out". If the relay drops out, it opens up, and fails to relay the current.
 I wouldn't overlook a bad ground tho. Most elect. issues are because of a bad ground.

[Fordeatinz71]

i was looking through my owner's manual doing research on your problem, and i don't know if the General changed it up in '85 but in '83, the T/L-CTSY circuit is the light switch, tail and parking lamps...and there is a separate circuit for INST-LPS which is the instrument lamps, the light switch rheostat, headlamp warning (never thought our trucks had that, i always thought the "headlamp warning" was when the battery went dead, lol) and the rear window defogger switch...then you have the HORN-DM circuit which controls the horn. cargo lamp (there's a good place to look for wiring issues if you have one), dome lamp, headlamp warning again (must be different for different models), lighter and clock...


so is your's different?  i thought the wiring arrangement was essentially the same in the ATC-fused models...

[VileZambonie]

Do not put in larger fuses. A fuse that blows is a good fuse not a bad fuse. Start by eliminating anything on that circuit that was added such as a radio, cb whatever. After that unplug the tailight harness and see what happens.

[85MudMonster]

thanks guys. found the problem. The stupid guy that owned the truck before me wired the trailer wiring harness up so that there were power wires being grounded out. Took off all the bad wiring and made it look good and rewired in my license plate lights and now everything seems to work well. I was thinking that it was the Gauge lights but thank goodness that wasn't the case. I noticed the trailer harness had a hot wire hanging down off of it, and decided to check more into it and found that the grounds where wired up to the hot wires. Anyway, Thanks for the responses guys. Oh and the delay was from that hot wire moving around while I was driving and grounding itself out.

[Fordeatinz71]

cool deal man!  i had a similar issue on an old '85 F2Sh!tty i had.  i went out to get in it one day and, true to form, it wouldn't start...the batteries (it was a diesel) were dead...totally dead.  so i jump it off, and let it run for about 15-20 minutes to recharge the batteries...turn it off and i notice the parking lights were on dimly...replaced the headlight switch and did everything i could think of, i was pulling my hair out...finally i start tracing wiring and i find that an old slide-in camper wiring harness it had was pinched (i had just carried a full load of stuff for my bud, so that had slid up against it and pinched the wiring) and the wires were arcing.  luckily the truck didn't catch fire, honestly.  i completely removed the wiring harness and never had another electrical issue out of that truck...it's amazing how people can jack up a perfectly good truck with hacked junk, ain't it?

[Captkaos]

thanks guys. found the problem. The stupid guy that owned the truck before me wired the trailer wiring harness up so that there were power wires being grounded out.

That was my next suggestion.  My DD 87 was done the same exact way..  No ground...