Darinm

Hi all, need some suggestions on some electrical troubleshooting.

Car is 1980 that just started having an issue with the stereo system.

Was putting a new carb on yesterday and noticed my Choke light was staying on so i pulled out the VOM and found i had 13 volts to the choke wire while the engine was running but once plugged in, it dropped to 1-1/2 volts. At the same time, i noticed my stereo wouldn't turn on so i went to the fuse panel looking for a blown fuse which i did find a blown fuse.

Replace it and the choke light turned off, but the stereo still wouldn't turn on.
Checking the wiring to the aftermarket stereo, i found the 12 volt constant was good with +12 volts, but the accessory only had 8 volts.

Using my VOM, i checked that same accessory and tried different ground points but still had the same 8 volts.. To confirm the lack of 12 volts was the problem, i made a jumper wires from an ignition point on the fuse panel to the accessory input on the stereo which allowed it to power up but only when the ignition was in the run mode. While probing for 12 volts on the fuse panel, i found the other accessory points also had only 8 volts, but ignition points on the panel were fine.

Any ideas what would cause low voltage ? Bad ground point for accessories ?

henrikse

When using your VOM attach ground to battery - This way you have a good ground all the time. Therefore if you read 8 volts you know it isn't ground and as well if you read 12 on battery and 8 where stereo ground is you know you have a bad ground.
8 volts could be from short. Check current on circuit to verify. If you are blowing fuse it is a short and you would have to isolate wires on that circuit.

Darinm

Sounds good. Will try that in the morning.

Im thinking it's something shorted since coincidentally I had to recharge my battery. I wrote it off as from just sitting.

Any idea what what else is in that circuit?

henrikse

No but pulled this 79 wiring schematic off Willcox site. Maybe you can blow up and print and see if it is the same

Cooter Tech

Did this problem start when you installed the new carb and electric choke? Any other fuses open?

Darinm

IN fact it did start with the new carb. My old carb had no choke so the choke lead wasnt in use.

I did as suggested above and when using my VOM with the ground on the battery, i get a full 12 volts on the always on lead, but only 8 volts on the accessory lead.

When i swap and put the positive lead of the VOM on the battery and ground to the ground lead i get the same 8 volts.

So this leads me to think it's a short on that circuit. I can trace the choke lead from the carb back to the firewall and it's clean with no breaks so up to that point, it's good.

henrikse

There is an interesting article on site. Search HEI and choke wiring. Seems there is a yellow resistive wire to the choke that some have used and resistive wire only has 8 volts on it. Coincidence?
If you disconnect wire off choke does radio acc still only have 8 volts?If you disconnect choke it would be exactly the way it was before you added carb and radio was working correctly? If yes then you will have to find out why only 8 volts on accessory wire. If you google accessory radio wiring there should be something out there that shows the circuit. It could be overloaded but likely a short.

Cooter Tech

Disconnect the choke wire. Then retest your voltages.

Darinm

So yes, if i disconnect the choke wire, the issue still exists. Based on the probing, i think there is definately a short somewhere. One thing i didn't do yet is to check the choke heater relay to ensure it's not what's causing the short.

Did i mention how hard it is to get to the fuse panel ? I can remember as a kid it was so easy to crawl around C3s when installing aftermarket stereos. Today its way harder. That footwell must have shrunk over the years :-)

Darinm

Yessir, tried that, same issue. The choke and accessories must either be on the same circuit, or use the same harness/connector which might be shorted ?

Cooter Tech

I know the misery of working under the dash, I feel like a walrus trying to get out from under it. Is there any chance the radio is causing the voltage drop? Did you disconnect the connector in the center console? The copper tabs get loose on the circuit board and will cause problems when reconnecting. These are from the 1980 manual on electric choke. I don't know how to resize them, sorry.

Darinm

Thanks, this is great info. The Radio is an aftermarket and no longer uses the factory connector. But i did in fact, disconnect the entire thing to see if that's what was causing the voltage drop. There is also an inline small amp (All Alpine) which i completely disconnected as well.

If i'm reading the diagram right on the fuse panel, it seems the Radio accessory power supply also supplies the wipers. I can confirm that by checking to see if the wipers work. I would imaging with only 8 volts, they would either work very slow or not at all.

Cooter Tech

Here is the entire page. Hope it helps

Darinm

Definitely helps. It will allow me to isolate the path into segments to hopefully see where the short is. I'll do more troubleshooting this weekend to hopefully find it.

henrikse

In schematics shown it says the radio is on its own 15 amp fuse and choke heater is on its own 20 amp which does not link them like your problem? Which fuse was it you replaced?
If all was well before you plugged in the wire for electric choke I would go back to that wire and check it off the choke to ground with an ammeter and ensure it is has no current. Then go to the radio turned off at the acc wire that has 8 volts and see what the current draw there is. Follow this wire back to where it is getting its feed and diconnect and check source voltage. With the wire disconnected once you find the shorted one you can use the ohmmeter and start moving it around at tight spots or suspect couplers to locate.
With everything turned off on car do you have a current draw right at positive lead of your battery?

Cooter Tech

The 8 volts you are reading sounds like it might be a feed back voltage. Are you sure it is not .8 volts or 8mv? All your fuses are good in the fuse panel? Check voltage ar red wire on alternator, then both fusible links on the starter post. Just suggestions. Good luck.

henrikse

good thought. Just go to a lower voltage scale and see if it pegs the meter. Quickly though. It may be ghost voltage as above.

Darinm

The blown fuse was the Choke heater fuse. 20 amp, upper right of the fuse panel.

I haven't checked the current draw at the battery yet, but certainly will.

I'm taking notes of what to check from all the replies since i won't be able to get back to it until this weekend.

The choke may be a red herring, but i'm checking both to be safe.

Darinm

Yes, sure it's 8. It's actually 8.something volts, i was just rounding the number.

Just curious since i will check it, but if the fusible links were bad, would it not prevent power to everything else ? So far, everything else is working electrically.

Darinm

Correct on the voltage and not below 1 volt. And yes, i did pull all fuses (as hard as they are to get to) to confirm they're all good. So far, only the choke heater fuse was blown.