our chevy

Hi All, we just joined the forum. Hopefully someone can help us. We have just aquired a chevy G20 explorer van from our father. My wife has only driven the van at night once and the dash lights and running lights went out. The 20 amp fuse to the "TLPS" ( Tail lamps) blew. It left us with no running lights and dash lights. The headlights work fine. I replaced the fuse and all seemed well. I put the ignition switch in aux. mode and all was still well. All lights and dash lights are ok. Now, is the kicker. Once I started the van, everything was ok for about 6 seconds, then the fuse blew, rendering the tail lights,side markers, and dash. The headlights were fine. I don't know what would cause this. If power is on and all works ok, what is making the lights go out ( and blow the fuse) in about 6 seconds after starting the engine.???? Its all good until I start the engine and after about 6 seconds I ( I think) hear a sound that pops the fuse. I replaced the headlight switch with a new one. Same scenario. I don't get it. The only thing I have done is replace the bulbs in the dash cluster, which were burnt out. The bulbs were issued to me by my local auto parts store. I assumed they were correct.
It just not make any sense. Everything works fine until I start the engine. Once I start the engine.....6-7 seconds later I loose the side markers, running lights and dash lights. Whats blowing the fuse?????
Any help would be appreciated.
Thanks to all that can help.

EinST

Welcome to the forum. There's obviously too much drain through the TLPS fuse. Based on the age of the vehicle, I wouldn't be surprised if the wiring had been modified. Have you tried removing the bulbs you've installed?

our chevy

No, I have not removed the bulbs I replaced in the dash cluster. I would not think that would cause the problem, but I'll give it a shot. This is a conversion van, so I am sure some of the wiring has been played with at some point in time. There is an aftermaket (old) radio in it that acts up and from the looks of the rats nest of wiring to the radio does not help things. I am tempted to rip that old radio out of there.
I can pull the dash light bulbs though for piece of mind. I just don't understand why everything works fine until the engine is running. Even when the ignition is in the start position (buzzer souding) all works until the engine starts and runs for about 5-6 seconds. Thanks for the help.

EinST

Higher voltage means greater current for the same resistance in the circuit. If the total current draw were near 20A with engine off, it could exceed that threshold once the alternator kicks in. Normally a circuit protected by a 20A fuse should not be carrying anywhere near that.

Viv

In a 1994 g20 Chevy Van I recently replaced the dash lights and my Tail LPS fuse also blows only after starting the car.... Definitely gonna mess with/take out the lights I replaced and see if it fixes it.

Viv

Update: seems to have been a coincidence. Took out dash lights and no change. Definitely quite the short as it will also blow a 30 amp fuse. There also seems to be one of my back side taillight bulb blown so imma replace that. Don't think it's the problem but gotta do it anyways.