280SE 4.5 wiring issue help needed

[billhard]

I found a previous owner's bandaid electrical work on the starter / battery/ coil block that sits below the washer fluid tank. Two of the terminals have been jumpered together, can anyone tell me why this might have been done and what the correct fix might be? If I remove the wire the car will only run when the starter is engaged but then dies when the key moves to the run position.

[ejboyd5]

From the description it appears the jumper could be a by-pass of a faulty ballast resistor. The resistor is designed to limit voltage to the ignition coil once the engine has been started and full 12V is no longer needed for continued operation. Of course, all bets are off in your particular case depending upon the number of band-aids applied by the PO.

[Graham]

It looks to me like the ignition system (first resistor. 0.4ohm) may not have been getting power from the ignition switch, so they tried to pick up 12v from the starter.

During starting, 12v is supplied from the starter on the ignition module side of the 0.4ohm resistor (red/violet wire from the connector block you showed), but that is normally cut off once the car starts.

Perhaps the jumper was an attempt to maintain the 12V after starting? If so, this would mean that with jumper in place, there should always be 12V at the ignition module side of the 0.4ohm resistor and car should run even after starting. However, voltage will not be dropped through the resistor and you may eventually have problems with the ignition system components.

In any event, the jumper should not be there. And with jumper removed, you should get 12V at the ignition switch side of the 0.4ohm resistor when you turn the ignition key on for the car to run. I suspect there is a problem in the ignition switch or the wiring from there to the resistor. Try to get things back to original setup.

Wiring diagrams may help. Probably same as the 72/73 107s (and available on-line at Startekinfo). The one below shows a line with arrow to terminal 16. That is the red/violet line to the terminal block and normally would only have 12v during starting. But with jumper, it is probably always live (even with key off!)



In this diagram, C105 is the 3 gang connector. Suspect jumper may be as shown.

[billhard]

Thanks, I'll study those and try to make sense of it. I am pretty weak when it comes to reading wiring diagrams.

I did however suspect the ignition switch when I first saw the jumper because the switch itself was quite worn, you needed to hold the key in just the right spot to get the car started. So I changed that switch out with a new part. The key position is no longer fiddly but the car still needs that jumper to run.

This may or may not be related, but I also have a strong battery drain with the key in the off position, 8-10 amps. I have pulled every fuse trying to isolate it but none did. This battery drain is relatively new seeming to have started after I had a new starter installed. Seeing as all this is in the same neighborhood I can't help but think they are all related.

[Graham]

Originally Posted by billhard

This may or may not be related, but I also have a strong battery drain with the key in the off position, 8-10 amps. I have pulled every fuse trying to isolate it but none did. This battery drain is relatively new seeming to have started after I had a new starter installed. Seeing as all this is in the same neighborhood I can't help but think they are all related.

Have you checked the battery drain with the jumper disconnected?

If the jumper is the way I depicted it would always be connected to the ignition module and there would be a battery draw, especially if points stop in closed position. But 8-10Amps?? That would run your battery dead in just a few hours.

Remove jumper and check the voltage between the 0.4ohm resistor terminal and ground with ignition switch all way on, but not to start. If the switch and wiring are good you should see ~12V. If not switch and wiring needs checking.

[billhard]

So the battery drain is being caused by the jumper wire.

Can you tell me where the 0.4ohm resistor is in the engine bay? The wire goes into a closed loom and I can't tell where it comes out. Does it look like this?:

[Graham]

Originally Posted by billhard

So the battery drain is being caused by the jumper wire.

Can you tell me where the 0.4ohm resistor is in the engine bay? The wire goes into a closed loom and I can't tell where it comes out. Does it look like this?:

Yes. It should be over just below the ignition coil on other side of engine bay. Something like this:

[billhard]

Graham,

Thanks for all the help! I found the resistor and toned it back to the red/violet at the electric block to be certain I had the correct one. The resistor is in fact getting 12V from the ignition switch when in the run position but it does 0 volts cross the resistor. So it seems the resistor itself is the culprit. I have order a Bosch replacement and will know for sure in a day or two.

[Graham]

Originally Posted by billhard

Graham,

Thanks for all the help! I found the resistor and toned it back to the red/violet at the electric block to be certain I had the correct one. The resistor is in fact getting 12V from the ignition switch when in the run position but it does 0 volts cross the resistor. So it seems the resistor itself is the culprit. I have order a Bosch replacement and will know for sure in a day or two.

Hopefully that's the problem! Let's know how it works out.

[billhard]

Finally had time to replace the ballast resistor and now I have another issue. The car starts but then stumbles like a cold car with no choke and dies. If I bypass the resistor it starts fine and settles into idle. Mind you it's not cold here in San Diego.

[Diseasel300]

Out of curiosity do you have the OEM ignition coil, or do you have a replacement installed? I had an issue like this on an old Onan engine with a replacement coil. The original setup used a ballast resistor, the replacement said not to use one. With the resistor installed, it wouldn't run to save it's life. Deleted the resistor and it's been fine since.

[billhard]

Just as a follow up for anyone else experiencing similar trouble, as suggested above the coil was also bad. The car appears to run well now with a new coil installed.

Thanks again for the help.

Bill