O.k. here is the problem I am having and would just like some insight... I bought some led taillights for my 72 blazer and they look great. The problem is when I go to turn on the headlights the turn signals will not work,but the brake lights and running lights do work. With the headlight switch off the signal's,running lights and brake lights all work great. Here is what I have done so far.. Tested the lights in another truck (and they work)new rear harness,new turn signal cam,new e-flasher(2 of em)new headlight switch,dimmer switch,and breaklight switch. Grounded the led lights to the buckets,then grounded the buckets to the body and checked and cleaned all 5 of the factory grounds. I used a fluke meter and am getting 12-13 volts to both the taillights. The one weierd thing that is happening is when I trun the headlight switch to dim the dash lights the rear side marker light flashes but as soon as I turn the knob back to where the dash lights are on the front marker light flashes just as it should. Any help would be great I am guessing its new harness time???

Did everything work OK before the LED lights? If so, I wouldn't think your harness is the issue. If you're not sure, get some regular bulbs and see what happens.

If I use regular 1157 bulbs it works fine but if I use 1157 led style lights it works but really slows the signal flash down??

Just tried em out in my friends 66 chevy and they work great just not in my 72?????

Isn't there some relay you have to run on these trucks when you switch them to LEDs?

I think it has to do with LED's having a lower current draw;seems to me there's special flasher units made for LED applications available through places like Speedway and also from Painless Wiring and Ron Francis Wire Works. I'll bet that'll make everything work right.

For turn signals to work correctly with the LEDs (which draw a lot less current) Try an electronic flasher unit. Also where are the 5 grounds. I am having problems with a taillight ground.

Terry the five ground sare as follows passenger side inner fender well to frame,body to front cab mount,rear crossmember to body and last is one per valve cover to firewall. The problem I am having is currant backfeeding thorugh my hazard system and I can not fid the source so since the harness is 30 plus years old I am gonna just replace the whole harness..