Electrical Issue 1976 Lincoln Mark IV


I have been very lucky so far with a 1976 Lincoln Mark IV, she is a beauty and in great shape. I drive it every day. I bought in SC but live up in Maine. At the beginning of the winter I used the blower. I would switch the car off take keys out of ignition come back to car an hour later and blower is on with no key in the ignition. This doesn’t happen anymore. Recently indicators won’t work. If headlights are on they’ll come on but not flash. Headlights off and I get nothing. Then last week the police pull me over because break light was out. He said left one was out at stop sign then right one was out when I pulled over? Local mechanic says salt on roads may have deteriorated a wire and i have a short. I’ve checked all connections front and back and don’t see a short. Mechanic says it would be very labor intensive and expensive to search for a short throughout the entire car. I’m not a rich man ? My gut feeling is it might be a short in the ignition. Should I suck it up, replace ignition and hope that’s it or does any one else have better advise (sorry its such a long question/comment - Jake

The turn signal switch may be where your brake light problem is.

No way related to ignition switch. Shorts cause blown fuses, opens cause inop.conditions ( I guess you could say blown fuses cause inop. conditions)

I also vote for T/S switch.

Has anyone installed a blower “afterblow” kit? These keep blower on after key removal

Perhaps you can get a switch and “stub” it in to test with.

I was just guessing ignition because blower shouldn’t be getting power with key out of the ignition. I guess I can focus on T/S switch. Should I do a short test first on all circuits using test light on negative terminal and removing fuses one at a time,or will this not necessarily tell me anything about the T/S switch

Since the brake light and the turn signals share the same bulb filament in the rear the brake light circuit runs through the turn signal switch. If the T/S switch is off then both the brake lights should turn on but if good contact isn’t being made through the switch then one side or the other may not work. Since you stated that the indicators aren’t working you might start by replacing the flasher unit. Maybe that will fix both areas. If it doesn’t you may have to replace the turn signal switch or clean the contacts at least.

The blower trouble may have been due to a problem that can happen with solid state motor controllers. If your speed control is the variable type the controller is tied directly to power and if shorts the power goes to the blower even with the key off. You stated that the trouble isn’t happening now so that may not be what happened. If the ignition isn’t turning off you can verify that with a test light probe.

You would be wise to invest in a service manual that has a good wiring diagram. Having that will save you more money than anything by following it and using proper testing procedures on the trouble areas.

Yeah I have all the original shop manuals but I am definitely no mechanic so It’s hard to understand wiring diagrams. The information you have given me is very useful. I never realized the blower could access power even with key off. I think the t/s switch is definitely where i should start although turn signal will illuminate when main headlights are on but wont flash. Turn headlights off and no turn signal. So maybe its flasher unit? Bulbs are definitely good or would not get anything

You are describing a very basic parasitic draw test. I realize you say you are not a mechanic so I will go easy, not every electrical problem is caused by a “short” but that term is the only electrical term many people know. How does it go, when the only tool you have is a hammer every thing looks like a nail?

Just unplug the switch and see if the blower sympton stopps.

Thanks All for everything. I did some more tests. With ignition off BOTH break lights come on. With car running both break lights come on. Signal Left with T/S and left break light goes out, Signal right with T/S and right break light goes out. SO would this be a faulty flasher unit or would it be faulty T/S switch. P.S Hazards work fine.

From what you state in your last post it sounds to me that everything is normal, right now at least. The brake light is supposed to turn off with the turn signal because both systems use the same bulb filament. If the brake light didn’t turn off there would be no turn signal indication, in the rear at least.

The problem you had may be intermittent so it might happen again later.

It was the Flasher Unit. $2.00 at NAPA and the Case is Solved ! Woo Hoo. thanks for all of the advise, without you guys I’d probably still be looking for a short - Thanks Again. I’ll ignore the blower for now as it’s not happening any more. Winter months up here in Maine can be brutally cold, maybe the cold caused variable speed controller for blower to freeze in place

Do you see how sometimes we must dismiss you (the customers) link between symptons? All adding the mysterious blower motor condition did was confuse things.

Glad you got it working ok and thanks for the feedback.

If the blower motor isn’t turning on now then the speed controller most likely now has an open condition and power isn’t getting to the motor. Proper testing will tell you if that is correct or not. Check for voltage on the leads. When the unit is supposed to be full on the control lead will have a small voltage (maybe around 5 volts) and the other two should have battery voltage on them. You should be able to locate the controller by following the wires from the motor. They will connect to the speed control. New units are around 100 dollars.