Electrical troubleshooting

[inchoate]

Went to finish up a few little things on my car today and low and behold I've suddenly got electrical issues.

 

I've got brake lights, a horn, the starter, the windshield washer pump, the brake fail switch and the high beam flashers.  Nothing else works. No turn signals, hazard lights, windshield wipers, heater fan etc.

 

I checked the fuses visually and with a multimeter and they're all good.  Relays all pass the click test.

 

Any thoughts as to where I should start looking?

 

Car is a LHD 1987 Caterham De Dion.  I replaced/relocated the battery and replaced the ignition coil and distributor recently but I didn't change any of the wiring.

Edited February 7, 2023 by inchoate

[MV8]

The distributor and coil wiring is part of the keyed V+ in the RUN position, along with everything that isn't working. Did you check for V+ in RUN at the fuses or just check that the fuses are not blown? Have you run the engine since changing the distributor and coil?

[inchoate]

This is the first time i've turned the key on since changing out the battery/coil/distributor.

 

Easy enough to check for voltage at the fuses and coil.

 

Edit...

 

I've got battery voltage at the coil with the key on and zero with the key off.  I've got continuity between the coil ground and the chassis ground.  I briefly had turn signals while I was messing around but that was the only thing working and they're MIA again.

Edited February 7, 2023 by inchoate

[MV8]

Check for continuity between the coil + terminal and the fuses, key off.

[MV8]

There should be a double terminal at the ignition switch. One wire goes to the coil + and the other provides B+ to the heater, wiper, and radiator fan fuses. You can try reseating the connector on the ign sw.

 

Note how much less the voltage at the coil is compared to what is measured at the battery. Use a digital meter (DVM).

Make a 4-6 foot jumper tool with 16ga wire and alligator clips for testing when the meter leads don't reach.

[inchoate]

I had a chance to sit down with my wiring diagram and it came to me that I unplugged the ignition amplifier while I was doing some cleanup in my engine bay.  Dollars to donuts that's the problem.

[MV8]

Those circuits do not actually run through the ignition module/amp per the '87 schematic.

An alternative to the fuses 2/3/4-coil+ continuity check (key off) is to check for voltage at the fuses.

[inchoate]

OK, sounds like a plan.  I guess I know what I'm doing this weekend.

[inchoate]

well, I've got turn signals and hazards now.  still no headlights (high beam flashers work), windshield wipers (windshield washer does work), heater fan or instrument lights.

 

i'm working with the wiring diagram but i can't seem to figure out what the non working stuff has in common.  I was messing around in the pedal box but i checked all of the wiring around there and nothing looks loose.

[MV8]

It sounds like the light switch is corroded/bad and common to much of the lighting and likely since it carries many amps without a relay and is receiving B+ if the headlight flasher is working. When the switch is on, the red wire should have B+ to the left lights fuse and right lights fuse with instrument lights. Once sorted, consider a relay for low beam to extend the life of the switch and have more volts reach the lamps.

 

Do you have B+, key in RUN, to fuses 2,3, and 4?

Edited February 21, 2023 by MV8

[jbcollier]

Stop trying to find the missing link/source of the Nile/etc.  Take one simple circuit and trace through until you find the issue.  I would start with the heater fan as it should not be complicated or controlled by any black boxes.  Use a 12v test light with an incandescent bulb.  Digital multimeters can "smell" a voltage through poor and corroded connections as they apply virtually no load to the circuit.  Sort that and move on to the next simplest circuit.  You might find one issue that rules them all but more likely it will the usual cacophony of causes.

Edited February 21, 2023 by jbcollier

[MV8]

Here is a basic headlight diagram for an '87. Not all connections and no grounds are shown for simplicity.

[MV8]

If you want to add relays for brighter lights, more effective cooling or potential fan upgrade, longer switch life, etc.....

[inchoate]

A bit ago I ordered up some new dashboard switches as mine are badly faded and I did have a thought that the 40 year old switches might be part of my electrical problems.

 

Today I finally got a few minutes with the wife and kids out of my hair and in every case it was the switch, so problem solved.  I've taken a preliminary look inside some of the old switches and they look a little squirrely but not terrible.  I'll clean them up and see if I can't dye the rockers back to black.  If I can get them to work I'll put them back into service because as they say, it's only original once.  If not it's no big deal because there's no such thing as a stock Caterham.

 

I'm happy it was something simple as I really didn't relish the idea of tracing out the individual circuits.

 

Thanks for everyone's help.