Ford Mustang Forum banner
Status
Not open for further replies.
1 - 10 of 10 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter · #1 ·
I bought a 1970 Mach 1 several months ago and I was having a few electrical problems. I have been busy and I am just now getting around to working on it. The first problem I am having is when I turn the headlights on my turn signals start acting erratically. The right flashes very slow and the left comes on but doesnt flash. When the headlights are off the turn signals function properly. The second problem is my dash lights wont come on when I turn the headlights on. I have already replaced the bulb so that is not the problem. The third problem is the turn signal indicators do not work. Well, actually the left one came on once for a couple minutes several months ago. The fourth problem is I stopped at a gas station and when I turned the key off the car continued to run as did the stereo. :headscratch: Any help/suggestions would be greatly appreciated. Sorry if these are dumb newbie questions, I am just starting to learn mechanics.
 

·
Registered
Joined
·
131 Posts
WOW! I don't blame you for feeling a little overwhelmed. That's a lot of weird stuff going on. Get a good wiring diagram and a decent multi-meter that will check volts, amps, resistance (ohms) and continuity. Then here's what I would try...

1) Get under the dash and check for any signs a previous owner modified the wiring. You never know what some folks will do and they don't always get it right.

2) Replace your headlight switch and your ignition switch. They are both fairly inexpensive and could solve a lot of your problems.

3) You may have a problem with your turn signal cam switch in the steering column. It's a little bit more trouble to mess with than the switches above but not too bad.

If you still have problems I would say your going to have to start tracing wires. This is where you absolutely NEED the wiring diagrams and the meter.

There are lots of smart folks on here so don't be afraid to keep asking questions. Someone will figure it out if you give them enough info.
 

·
Super Moderator
Joined
·
40,152 Posts
i agree with above,replace head light and ign. switch.check the grounds coming out of the light circuits underhood in the front and in trunk in the rear.remove,clean,see if that helps.
 

·
Registered
Joined
·
90 Posts
Electrical problems like yours can seem pretty mysterious, but keep in mind you own a car with a relatively simple electrical system (no computers!). Get a wiring diagram and study it. Everything comes out of the positive terminal of the battery, goes to the switch or device, then returns to the chassis.

It's also great that there is a lot of room under the hood. In 1995 on a trip from San Francisco to Pasadena on Hwy 101, I was stuck at a fast food restaurant with my 1967 coupe and could not get it started. After a half hour of checking the wiring I noticed a bare wire on the harness near the firewall. It turns out my neutral/park switch wire was burned through and was shorting to ground. No way I could have found that on a modern car. I wrapped it up and went on my way. When I got home I taped it with electrical tape and it's still there.

I agree with the comments above about the switch replacements. I don't see how a bad headlight switch would affect your turn signal, but it's a cheap fix to replace both, and also the ignition switch. You should also do a careful visual check of the entire electrical harness from under the dash to the front of the engine compartment to see if there is any obvious damage.

Good luck!
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #5 ·
WOW! Thanks for the prompt and in-depth responses.

There has been quite a bit of modification done to the electrical system to hook up the aftermarket stereo which I have also had problems with. I will take the advice and replace the swithches. I have priced them and the head light switch is inexpensive but the ignition switch on a 70 is quite pricey. My buddy bought some property with about 20+ old mustangs on it and I believe there are a couple of 70's, do you think it would be worth trying to pull the switches out of these old ones and trying them or do you think they could be bad from sitting for many years? I would rather not spend 100 bucks on and ignition switch if I dont know for sure that its a problem.
 

·
Registered
Joined
·
131 Posts
It never hurts to try. If you can get one from your buddy for nothin' or next to it...give it a shot!

I can see the headlight switch affecting the turn signals because of the way he describes it. They start acting up when the headlights are turned on. My guess (and it's nothing but a wild a$$ guess) is the damaged headlight switch may be pulling too much amperage. Your flasher is timed by amperage draw, that's why you see guys with trailers whose blinkers go 900 mph...they didn't upgrade the flasher unit to compensate for the added amperage pulled by the trailer lights in the circuit. The headlight switch may be pulling amps AWAY from the turn signal circuit causing the flasher to run slow or erratically. It could also be a bum flasher unit and the headlight thing is just a coincidence, but I kinda doubt it, they usually go out completely or not at all.

Just my 2 cents.
 

·
Registered
Joined
·
7 Posts
i have the same thing going on still looking for the problem. going to try what you guys told him (1970 coupe )351c
 

·
Registered
Joined
·
58 Posts
I am sure that this is a ground problem. Check and replace the -cable from the battery and also see if U can find any rusty connection to the chassie.

When U have problem with the lights, one way ot the other it is almost sure it´s a ground problem.
 

·
Registered
Joined
·
3,166 Posts
Electricity always seeks the path of least resistance. If there is a bad ground connection the electricity will back feed through bulbs and wiring seeking that path of least resistance and causing those weird problems. You really do need a schematic diagram and check those ground connections. Even one bad ground can leave you scratching your head to a nub. Fixing even one bad ground can also work like magic and all kinds of problems will be fixed.

I do agree in changing the H/L and ign. switch, even a used one would be worth a try. The ignition switch on the 70 is actuated by a rod from the key down the length of the column to the switch at the column's base. This rod may be binding on something inside the column and is the reason that you couldn't turn the engine off.

You may want to gather all of the ign. switches that you can, they're not even listed in the National Parts Depot catalog. This is a good indication that they're hard to come by. If you do need a new one, NAPA is where I'd start looking.
 

·
Registered
Joined
·
112 Posts
I agree with the headlight switch. One thing to remember with parking / turn signal combo is that Ford wired it like this:


chassis<| lamp <-------- parking +
ground <| socket <-------- turn +


You see with that wiring, you can't use regular LED bulbs or things stop working. Also, a short on the one side of the socket causes REALLY weird issues like turn signal light lighting up on the instrument cluster.

That being said, also check the (front) turn signal sockets for corrosion and shorts.

I'm pretty sure you already figured it out, but just for reference when next guy has same issue... :)
 
1 - 10 of 10 Posts
Status
Not open for further replies.
Top