Hello:

Here is my situation. With the headlights and park lights off the turn signals work fine. When I turn on the park or headlights the left turn signal doesn't blink it just stays on.

When I have the headlights/park lights on and turn on hazards both turn signal sides don't blink they actually go a little dim on the instrument cluster.

The brake lights work with the headlights on and without.

With the headlights on the cruise control doesn't work.

This truck has a topper with a high mount brake light ( led ) on the back. With the headlights on it turns on and also goes brighter when the brakes are depressed. When the left turn signal is switched the high mount brake light goes out.

Any ideas? I have subscribed to alldatadiy.com so I have all the wiring diagrams I just can't see how all these problems work together. I know I must have a bad ground or some wiring problem I just don't know were to start.

Any help is super appreciated.

 

Start with isolating the cap CHMSL and retest

Next, check both bulbs on the left side, test with external 12 V DC power.

I am suspecting a bad ground on either the front or rear parking / turn ( & stop for rear ) sockets.

The reason it works with the headlamps off, is the turn signal is using the parking lamp circuit to find ground. When power is applied to the parking lamps, ground is no longer available for the turn signals.
Same reason the CHMSL is on dim ( and I would guess the truck's stop lamps, you just cannot notice with them installed ) with the headlamps on, bleed to ground on the faulty bulb connector, illuminating the CHMSL.

The CC will not work if there is voltage on the stop lam circuit, you have just enough to trigger this with the derived ground.

 

I pulled the front and rear left turn signal bulbs and removed the bulb and removed the socket and checked the black wire to ground with 0 ohms in the front and .3 ohms in the rear. The voltage drop in the rear is .3 vdc on the ground.

I really appreciate your help on this and the speedy response.

 

Did you do the cap CHMSL isolation ?

You need to remove it from the aftermarket CMHSL pigtail on the factory wiring.

 

I did not do that. I didn't understand what you were writing about. How do you cap the chmsl ? is that simply disconecting it from the harness?

I will do that and retest.

Thanks again for the help

 

Isolate the topper with a high mount brake light from the factory system.

Sorry I called it a cap.

 

I just had this exact same (very strange) electrical problem. It ended up being a short in my trailer wiring harness. I noticed it was a bit corroded so I cut the wires to it and everything was instantly back to normal.