'71CS

If I turn the lights on just the headlights come on..no tail lights or side marker's but if I hit the brakes everything lights up as it should and if I put the turn signal on it works as well. It also keeps blowing the tail light assembly fuse as soon as I pull on the light switch. I see a brown/white wire hanging down in front of the fuse block with one end running behind the block and the other end loose but I can't say if this is a new thing or I just never noticed it before because the car is still relatively new to me, maybe from a previous owner splicing/hacking into something. Any help would be much appreciated and the car is my '71 olds cutlass supreme. Thanks a lot.
Trevor

jaunty75

You have a short in your car's taillight circuit.

I had a similar problem with my '73 Custom Cruiser. Headlights/hi-beams worked fine, turn signals worked fine, but the fuse for the taillights would blow the moment the headlight switch was pulled out.

I ended up tracing the wiring from the front of the car to the rear using one of those short finders:





The problem ended up being a pinched wire in the left rear taillight housing. The car had been repainted, and I'm guessing the paint shop people didn't pay close attention when they reattached the taillight trim to the car.

joe_padavano

First of all, the turn signals and brake lights use one of the two filaments in the 1157 bulbs. The tail lights and front parking lights use the other filament. The circuits are completely separate except for the common ground on the bulb.

I also assume that when the fuse blows, the front parking lights don't work either.

If so, you need to find the short in the park/tail light circuit. Start by looking at the wiring diagram in your Chassis Service Manual, where you will find that there are a LOT of things hanging off that fuse that could be the source of the problem. The CSM wiring diagram will also tell you that the brown/white wire is the feed for the park/tail light circuit, so that is a highly suspect wire.

'71CS

Thank you very much Jaunty and Joe for the responses, much appreciated.
I will focus on that brown/white wire and see where I get with that.

71cuttyAndy

joe_padavano

Welcome. Now go back and read post #3 in this thread.

'71CS

Hi Andy, ya my issue in particular was a bad rear tail light bulb, I took the lense covers off and started going through them bulb by bulb and found one that was really badly corroded and bridged the two contacts together so as soon as I pulled the light switch it instantly blew the fuse. I guess I was lucky it didn’t end up being a wiring issue just a bad contact point.

71cuttyAndy

what exactly did you do to fix the problem? I'm checking every possibility, this is the only forum I can find on the internet. If you can give me exactly what you did to fix the problem would be highly appreciated.

71cuttyAndy

thank you, I really appreciate it. I'll look there now. What's weird to me is I disconnected the back harness and once I pulled the switch it still blew the fuse. Do you think it's a bad bulb in the front parking lights?

'71CS

Well check your bulbs first and see if that’s where the problem is and if it is then we can go from there..you would have a few options depending on the condition of your bulb sockets with varying degrees of getting them back in shape.

71cuttyAndy

Will do, thank you!!

'71CS

I’m thinking it would have to be the front part if you disconnected the back.

71cuttyAndy

me too, thanks again. I'll keep you posted. I'm hoping that's the issue for me and no wiring issues fingers crossed.

joe_padavano

The pigtail that feeds the underhood light is on the same fuse. It's not uncommon for that pigtail to get pinched or otherwise shorted when people don't realize it's there. That will cause the fuse to blow immediately when you turn the lights on. Look for a pigtail coming out of the firewall harness below the brake booster.