Interior lights... 78 SC Targa

[tcar]

Interior lights don't work.

Fuse is OK.

Can anyone point me to a possible cause/fix... not a wizard w/ electrics.


(PS - Clock doesn't work either and it did... same circuit?)

Interior lights, lugage compartment light and clock are on the same fuse #18. You say not to be a wizard with electrics, but are you able to check the voltage at the fuse with a multimeter or a light? That would it make much easier to help you in a systematical procedure to find the cause of the problem.

The fuse box with the torpedo fuses is not very reliable. Oxidation of the brass fuse clamps is quite common. In addition, bridges between two hot sides of fuse terminals at the back of the fuse box also tend to "rust" and cause poor connection.

The hot sides - from the battery - of fuse #17 and #18 are connected at the back. Wiggle carefully at the terminals of these fuses and see what happens. Your Luggage compartment light is your reference - if it worked before ...

Otto

[pete3799]

Yup.....same circuit.
Remove the fuse and clean the contacts.
Good idea to remove them all and shine them all up. A Dremmel with a wire brush works great for this. Disconnect the battery first.

[porwolf]

You will have to digg a little deep into the electrics. First, there is no factory installed fuse for interior lights like the instrument lights. Fuse 18, named interior lights, only supplies power to some interior lights like the glove compartment and hood lights. The instrument lights are fed by terminal 58A on the back of the main light switch on the dash board. Those lights are not factory fused, but should be. You should check whether there is power on terminal 58A on the light switch when lights are supposed to be turned on.

Here is are a couple of links that might help understand the interior light electrics better:

Dash Lights Stay On

Headlight Switch Removal/ Turn Signal Switch Install on '89 Targa

@Porwolf

I thought he only mentioned that the clock did not work either. The clock, needing permanent 12 V like the interior and Luggage compartment lights, are using the same unswitched fuse #18.

Otto

[tcar]

Originally Posted by Otto H. Wegkamp

@Porwolf

I thought he only mentioned that the clock did not work either. The clock, needing permanent 12 V like the interior and Luggage compartment lights, are using the same unswitched fuse #18.

Otto

Thanks...

Correct, clock stopped working.

But the gauge lights work fine.

It's the clock, dome light, glovebox and trunk light that don't work.


I checked the clock leads (ground and power) with the meter and got nothing. It's supposed to be hot all the time, right.

Battery (Optima) with car not running shows 12.37V.

[911Freak]

Most likely ground issues. If you have the Bentley manual for your SC it walks thru a lot of this.
Briefly, there are clusters of ground wires (usually brown) at several locations on the chassis that have to be 100% functional for most systems to work properly.

One such location is in the front bonnet area behind the gauge cluster, bolted to the inner fender/shock tower right under neath the hood. This area gets exposed to a lot of weather/water and is a common ground fault suspect.

Check for loose, frayed or burnt wires.

This was the ground wire cluster that caused a lot of dash/interior faults on my SC. Some knuckle-head hacked them up and they fried my power window wires. All replaceable & repairable.

Follow the manual for troubleshooting electrical faults to the letter and you can learn and repair almost anything on these old cars.

Good luck!

[theiceman]

It's not a ground issue,.it's a supply issue, the whole circuit is dead.

take it to someone who knows electronics if you can't use a voltmeter to systematically check through circuit for 12 volts.

[tcar]

Thank you... yep circuit is dead.

My car has fewer fuses, I think, due to, I think, less equipment from the factory. No Cruise, no power windows, not fogs, no A/C. I doesn't have all the fuses listed on the cover.

So is the 18th fuse the 18th from the front of the car? (have a Bentley)

[javadog]

Look for a loose connector in the trunk, below/behind the fresh air blower.

JR

[theiceman]

yup i have a 78 with no options either. if you look on the inside of the plastic fuse cover its there. i cant remember which one. but check both sides if the fuse for 12 volts. i think the problem may be a broken wire or contact in this area.
just set your meter to volts put one lead on a good ground and the other on the positive side of the battery, once hou see 12 v there you will know what you are looking for ,.then move to both sides of the fuse and work your way ojt until you have no voltage, there wkll be your break.

[porschenut]

Tom, take your meter and touch one lead to the head of one of the fender bolts near the fuse panel. Take the other lead and touch it to the top side of the fuse position that protects the circuit in question. The lead should contact the copper (or brass) tab, not the fuse itself. Do you get voltage? If not, check the adjacent fuse positions for voltage. If you do get voltage on the supply side (top of the fuse), then move the lead to the bottom tab. If no voltage, then the fuse is not working. It may simply be corroded to the point where the resistance is so high that there's not enough current available to power the circuit. Just because a fuse isn't blown doesn't mean it's okay. Swap that fuse with its neighbor to see if it resolves the problem (or use a new fuse if you have one). But if you do get the same voltage reading on the bottom tab as on the top one (with the fuse in place), then somewhere in the circuit wiring is a break that you'll have to go hunt for. The ground connection is the most likely culprit, since every load on the circuit is inoperative.

The rearmost fuse is number one, so count to number 18 moving toward the front of the car.

[tcar]

Originally Posted by porschenut

Tom, take your meter and touch one lead to the head of one of the fender bolts near the fuse panel. Take the other lead and touch it to the top side of the fuse position that protects the circuit in question. The lead should contact the copper (or brass) tab, not the fuse itself. Do you get voltage? If not, check the adjacent fuse positions for voltage. If you do get voltage on the supply side (top of the fuse), then move the lead to the bottom tab. If no voltage, then the fuse is not working. It may simply be corroded to the point where the resistance is so high that there's not enough current available to power the circuit. Just because a fuse isn't blown doesn't mean it's okay. Swap that fuse with its neighbor to see if it resolves the problem (or use a new fuse if you have one). But if you do get the same voltage reading on the bottom tab as on the top one (with the fuse in place), then somewhere in the circuit wiring is a break that you'll have to go hunt for. The ground connection is the most likely culprit, since every load on the circuit is inoperative.

The rearmost fuse is number one, so count to number 18 moving toward the front of the car.

Thanks, Dave...