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Turning on headlights kills engine? Help, please!


Reaper1
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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. confused.gif

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.

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Like Bob says, it is a cable connect; but it could be anywhere from the top of the steering column to the radiator core support. For this problem the most common cause that comes to mind is mice and the most likely place to find this is between the firewall and core support. Next most common cause is movement and over time if a cable isn't properly in place it can rub itself raw. This can even happen in the steering column, but for low beam position killing the car only when lights on, odds are against this being the location.

 

Car runs with high beams on dies with low can only mean that 12v for the low beams is going someplace it shouldn't and a good visual inspection of the wire harness is the first thing to do.

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Yup. Dug into it from the core support all the way to the firewall thus far. No signs of damage from rubbing, etc. No rodent damage. The car is surprisingly clean.

 

I am going to start with replacing the corroded fusible link and retracing my troubleshooting from today.

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Yup. Already there. I was attempting to isolate the issue from either being in the cabin or out in the engine bay harness, so I disconnected the bulkhead connector and I inspected both sides as I have seen those give issues before, especially with corrosion, but it was clean. This is honestly the cleanest cars I have ever worked on. That's also why this problem makes no sense.

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Electrically speaking the problem makes perfect sense, the where and the why that caused it could make for a good funny story; after it's found and fixed.

 

Divide by two is the best way to troubleshoot electrical and though it's not in the exact middle pull the headlight relay and if you can kill the engine by turning on the lights pull the fuse for the lights and try it again.

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I don't have my wiring diagrams anymore but was wondering if it is possible to bypass the dimmer switch in the column to eliminate it as a possibility.  I am assuming by your description that you replaced the headlamp switch because the dimmer for the dash lights was in bad shape, that should not be related to low and high beam headlights selection. The tilt function of the column may also be pinching a wire that goes from the dimmer switch on the column.

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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! thumb.gif

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

 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.

 

When you install the 16V engine, you have to have the 16V engine compartment harness! It is vastly different from that of the 8V setup. You will learn just how much 'fun' it really is to deal with the 16V engine.

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Well, alrighty then! LOL I can say that there's been a number of people asking about the harness differences and I honestly haven't looked to see what all they changed. I wasn't sure if they simply used jumper harnesses or if they actually redesigned it to truly fit.

 

I suppose in a round about way you just kind of answered the question! I think I'll lay the harnesses next to each other and then take pictures. I can also overlay them and take pictures. That might be interesting.

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Well, alrighty then! LOL I can say that there's been a number of people asking about the harness differences and I honestly haven't looked to see what all they changed. I wasn't sure if they simply used jumper harnesses or if they actually redesigned it to truly fit.

 

I suppose in a round about way you just kind of answered the question! I think I'll lay the harnesses next to each other and then take pictures. I can also overlay them and take pictures. That might be interesting.

I'm pleased for you that you got the harness along with the engine. Did you also get the Getrag transaxle, shafts and all related items?

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I own the entire vehicle. It's just that the chassis isn't as good as this car's.

I can understand that seeing it was driven in NJ and probably saw salt covered icy roads during it's life.

I use to live in Jersey, so I'm familiar with what happens to cars there having worked my early years as a mechanic in Hackensack.

That is what I love about the southwest, no-rust-cars. Even with all the miles on any given car we own, there is no rust in any of them from road-salt.

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