I have an 88 chevy full size truck. I am having electrical difficulties. When I brake, the light display for my heater dims. When I turn on my headlights, my tailights don't come on, and the turnsignals will come on and stay lit when I turn the signal. There are four wires going to the tail lights; dark green, light green, brown, and yellow. The light green, and yellow wires are left and right turn signal. The dark green is backup. The brown is from the head light dimmer switch. When I checked to see if a wire was grounded I found connectivity in the brown wire to ground, so I replaced the brown wire, still grounded. I need direction to what to do next please.

Thoughts:

1. Remove battery and clean terminals and cable connections.
2. Fully charge battery.
3. Make sure alternator is working properly.
4. Check headlight and turn signal switches. Contacts tend to get dirty and corrode, over time. First, try spraying switches with WD-40 or contact cleaner. Second, remove and see if you can service the contacts. Third, replace switches.
5. Remove and inspect taillights. Corrosion is the main problem here. Disconnect negative. Battery terminal and clean socket contacts. Spray with WD-40 and install new bulbs.

Check your bulb bases; a friend of mine had same problem.
Just my humble...