Electrical Problem - Where to Look

[Grant M.]

I've just recently lost both the brake lights (non-power) and the courtesy lights (kick panel as well as rear compartment) in my 1965 convertible. Tail lights and signal lights work fine. I can't say with certainty that they failed at exactly the same moment, but I have been driving the car a bit and only noticed that both systems were out when my wife mentioned my lack of brake lights as she followed me to our storage facility. It was then that I also noted the courtesy lights were out as well.

In trying to trace in the Assembly Manual wiring diagrams where these two systems intersect, I can see the "body connector" held by a clip to the dash reinforcement under the instrument cluster, and of course the fuse box, where each has its own fuse. Otherwise, the courtesy lights are activated by the headlight switch as well as the door jamb switches, and the brake lights are activated by the brake light switch which then sends power through the turn signal switch, but there appears to be no other connection between these systems. Can anyone suggest where else I should be looking?

Thanks,

Grant

[Jack H.]

Re: Electrical Problem - Where to Look

I think you're on the right track (checking the wiring diagram to see if the circuits are related)... Now, pull the respective branch circuit fuses, verify you have B+ on one terminal but not the other. Replace the fuses (one at a time) and step forward along the circuit path(s) to see where you lose power...

[Grant M.]

Re: Electrical Problem - Where to Look

Jack,

Understood and thanks. The fact that these circuits seem to be entirely separate except for going through the "body connector" had me thinking that it must be the common fault point, unless someone else has had experience with this problem and can steer me otherwise.

Grant

[Wayne M.]

Re: Electrical Problem - Where to Look

...The fact that these circuits seem to be entirely separate except for going through the "body connector" had me thinking that it must be the common fault point, unless someone else has had experience with this problem and can steer me otherwise.

Grant

Grant -- all the symptoms you describe point to a simple burnt out fuse; the bottom one, 15 amps. This controls brake lights and all courtesy lights (btw, your clock probably doesn't work, either). Signal lights are not affected by the brake light switch power. If your tail lamps, licence plate lamp, fuel guage and back-up lamps (if Z01 option) all work, probably the rear wire harness connector, that you describe clipped to the under-dash cross-bar, is all OK.

If this doesn't cure it, advise and we'll continue from there. Good luck.

[Clem Z.]

Re: Electrical Problem - Where to Look

a lot of GM cars have the brake light fuse tied into the same circuit as the dash lights or interior lights so you know if you have no dash or interior lights you also do not have brake lights

[Grant M.]

Re: Electrical Problem - Where to Look

Wayne and Clem,

Thanks for your advice. I know it sounds like "basic" electrical sense, and I did (visually) check the fuse (without removing it), but I'll pull it and replace it to see what happens. But if indeed it is blown, my concern would then be what caused it to blow?

The car's not at home right now as I'm nearing the end of a monumental task of a do-it-yourself epoxy coating job on my garage floor. I'll retrieve the car from storage tomorrow or Saturday and try a new fuse.

Thanks again,

Grant

[Wayne M.]

Re: Electrical Problem - Where to Look

... I did (visually) check the fuse (without removing it), but I'll pull it and replace it to see what happens. But if indeed it is blown, my concern would then be what caused it to blow? Grant

Grant -- Easier than pulling the fuse, get one of those pointed test probes (the handle glows with B+ contact) -- connect the aligator clip end to the metal edge of the bottom dash, then touch the pointed end to the outboard cap of the bottom fuse (should glow as is always live); then touch the probe to the right fuse cap -- won't glow if blown. Same with the other fuses, except some will only have (left cap) power if ignition switch turned to "acc".

[Jack H.]

Re: Electrical Problem - Where to Look

Another related malady is oxidation of the fuse box clips. It IS possible for original fuse blocks to oxidize once the original fuse that hasn't been out in many years, to oxidize along the fuse clip contact surface resulting in no/poor ohmic contact when a fresh replacement fuse is installed.

Result: good fuse but no/little current flow through the fuse to power that protected branch circuit.

Jiggling/wiggling the fuse in its holder can 'sand' through the oxidization resulting in the circuit(s) working again, for a while...

If this turns out to be the case, the correct 'fix' is to remove the fuse, brush the clip contact surfaces with a wire wheel on a Dremel tool, coat the clips with silicone grease and then re-install the fuse.

[Grant M.]

Re: Electrical Problem - Where to Look

Wayne/Jack,

Thanks for those tips. In fact, I did take the trouble a few years ago to remove all the fuses and do some rudimentary cleaning of the fuse holder clips with emery paper, but I didn't use any dialectric and it has been a while...

Grant

[Grant M.]

Re: Electrical Problem - Solved, thanks!

Jack, Clem, Wayne,

Thanks to you gentlemen for your advice/tips on dealing with my brake/courtesy light probem I can report success.

As suggested, the problem was indeed fuse-related, but the existing fuse was good; the retaining clips that provide the electrical contact were rusted/dirty. As I attempted to remove the existing fuse with a plastic fuse puller the courtesy lights came on. The brake lights however, didn't work at that point. Examination and some "jiggling" of the brake light switch, got them working, but it seems that the switch is somehow out of alignment with the brake pedal so that it isn't reliably activated. I didn't have a chance to fix it last night owing to time/lack of lighting in the store-it facility, but I now know what needs to be done and that's more than 50% of the solution...

Many thanks again, guys and happy 4th of July!

Grant