I'm slowly trying to fix all the little problems with my 88 coupe and I've got one that has me a bit confused. When sitting at a stoplight or traveling down the road my turn signals flash very slowly, when I put the car in park they speed up to normal. I probably won't have time to mess with this til the weekend, but I was wondering if anyone might know where I could start looking? I don't know if it's related or not, but the cruise control is inop. It doesn't seem to be getting any power, but the fuse is good. Thanks in advance.

 

Slow turn signals could be caused by low voltage,flasher or poor grounds. Heres some good reading on lights and cruise control.
http://members.shaw.ca/agent86/Exterior%20Lights.pdf
http://members.shaw.ca/agent86/Cruise%20Control.pdf

 

The flash rate is directly proportional to the lamp current through the flasher. More current, faster flashing. You have slow flashing at stoplights because you have the brake applied and stop lamp current flows through a common wire with all the other rear lamps to ground and also with all the front lamps to their ground. If the ground connection has resistance due to corrosion, the stop light current through this resistance causes the ground wire to have some voltage on it, lets say 2 volts (should be like .03 volts). Now your flasher lamp instead of having 12v on it, has 12v minus the ground wire voltage (in this example 2 volts), so your lamps that flash only have 10 volts which causes low lamp and flasher current and therefore slow flashing. Your turn signals speed up when you are underway because the brake lights are not on and there is smaller current flowing in the ground circuit causing not as high a voltage on the corroded ground connection, therefore higher voltage on the turn signal lamps. Brake light lamps do not flash, a separate 2nd filament in the brake lamp flashes to indicate turns.
What you should do is investigate the quality of the ground wire connection to the rear lights first, then the front. Rear lamp ground wires get connected together, then go to a connector and then to a bolt to chassis ground. Check the connector and the bolt to the chassis. The front lampsground get connected together and each side has its own ground making it less likely the problem is on the front lights, but check them also.

 

Thanks for the information. The more I read on this forum, the more it seems like most electrical problems are ground related. I'll tear into it this weekend and see what I can find. Thanks for the advice and information.

 

This is a little flaky, but here goes. The cruise switch went out on my 1988 too. a new replacement was pretty pricey. Thinking GM probably used the same switch in other models, off a friend went for a junk yard adventure. Turns out a Buick cruise switch of similar vintage was identical and got it for only a few bucks. I don't remember the particular model.

 

Thanks for the info. I love GM for the interchangability. The weather's getting good enough for junking so I'll see what I can find around here.