Turning on headlights kills engine? Need help, please.

[Reaper1]

I was getting ready to take my '89 8V Masi TC out for its maiden voyage the other night, but as soon as I turn on the headlights it's like I turn the ignition off.

To make it even more strange, if I turn the high beams on the car starts and runs.

I have done some initial checking and I did find a loose ground under the battery and the white fusible link that helps feed the ASD relay was corroded. I will replace that tomorrow.

I know the car did not have this problem before as I have run it several times with the headlights on. I replaced the headlight switch due to the dimmer being extremely corroded. Now the car has this problem. I then replaced the new switch with a good OEM one and the problem persists.

Beyond that I am at a loss. No other system causes this issue. It's only the low beam headlights.

I'm open to suggestions.

[BadAssPerformance]

If everything is wired correctly and nothing is shorted, corroded wires should be a good place to start. I was chasing a short in MB's Talon and was reading false shorts due to a corroded power wire.

[stewdaddy23]

yep, see if it dies when you hit the brakes. then check the cables on the the BATT.

[Reaper1]

It keeps running even with the brakes. The only system I couldn't check was the defrost because I don't have the hard top on it. Other than that, the low beam headlights are the only system that seems to produce the issue.

The corroded fusible link was strange, so I'm going to star with that. I am also going to retrace my steps that I did troubleshooting earlier.

[EaZyE426]

Just for S&G's, did you try putting your original headlight switch back in?

[Reaper1]

Yup. I did.

Update! I fixed it! Neither the loose ground or the fusible link were it, though.

After rechecking the car side and absolutely confirming the issue was on the engine bay side and knowing I had worked all the way from the headlight to the firewall Y-junction, I figured to check the other side. I found that the harness had rubbed on something (probably the power steering pulley) and 3 wires had touched and melted together. Low beams, high beams and a violet/white tracer that goes to the MAP were the culprits.

Not a fun area to work and I don't like the fact that I had to replace the fusible link with a fuse holder (no 22ga fusible links were available) and now those wires in that corner also have been repaired. So, I think when I do the 16V swap, the engine bay harness will also be swapped. I'm also seriously considering a PDC for it, too.

Thank you all for your help and suggestions. It's much appreciated!

[Moparbishi]

Just did a pdc on my shadow. Was really easy. Did it in about 4 hours

[Ondonti]

I have have a bunch of fusible links in the shop if you want to go harness chopping. I hate that fuse holder until it blows 4 times In a row cause the problem is still there. Then I love it.