JW355714 Posted August 13 Share Posted August 13 Hello, My name is Joe and I am from upstate South Carolina. My truck is an 86 F150, long bed, single cab, 4WD with a recently rebuilt NP435 (Greatest transmission ever, and you can’t change my mind). I bought the truck with a 302 out of a 1990 Mercury Grand Marquis in it and the wiring due to the motor swap is…interesting to say the least. Currently my only real issue is that the turn signals work great when no lights are on, get slower when the running lights are on, and don’t work at all when the headlights are on. I knew the truck was going to have electrical issues when I bought it a few years back, but it ran and drove so I just ignored the electrical issues until recently. I’ll spare everyone the long painstaking details, I started with replacing all of the lamp sockets all the way around (some of them were melted), and tearing out the trailer wiring harness that was crudely spliced into the wiring harness for the rear lights and creating proper grounds for the rear lights. Since then the turn signal switch and headlight switch have been replaced due to corrosion and wear along with the turn signal flasher and hazard flasher. All of the lights are now much brighter and the turn signals flash much quicker than they did before I started this monstrosity of a project, but still no turn signals when the headlights are on. Before I go any further with this project, a previous owner had installed on of the cheap aftermarket ignition cylinders from AutoZone and cut out a place on the dash below the instrument panel for it. I’m assuming the OE ignition system in the truck isn’t compatible with the engine, but I don’t know that for sure. I am not very good with wiring diagrams, but from what I can gather it seems like the turn signal switch connects straight to the ignition switch and thus the aftermarket ignition could be causing the low voltage in the lighting system leading to no turn signals with the headlights on? The voltage reading on the aftermarket gauge I have in the dash drops a whole volt when I turn the running lights on and another whole volt when the headlights are turned on. I’m hesitant to go any further given that the likely culprits have been replaced, so any insight would be much appreciated! Link to comment Share on other sites More sharing options...
Gary Lewis Posted August 13 Share Posted August 13 Welcome Joe! Glad you joined. Where in SC? I ask because we have a map (Bullnose Forum/Member's Map in the menu) and we can add you with a city or zip. On the turn signals, I'd bet that your problem is the ground for one or both headlights. In the schematic below, which is from the 1986 EVTM (Documentation/Electrical/EVTMs/1986 EVTM), you can see in the lower left that the left front turn lamp uses Ground 801, which is on the LH inner fender behind the headlights. But if that ground is bad then electricity in the turn lamp will actually go through the other filament in the bulb and try to power up everything on that circuit, which is a bunch. And those devices will work well enough as a ground for the turn lamp to come on - until you bring those other things on. The other things are the the LF marker lamp and the LF park lamp, which come on with the headlights. So when you pull the headlight switch on the turn lamp quits working. That is a classic grounding problem. So look for the black wire that is coming out of your turn signal lamp and follow it to the ground on the fender. Clean that ground up, as well as the one on the right side, and I'd bet your turn signals work when the headlights are on. Link to comment Share on other sites More sharing options...
grumpin Posted August 13 Share Posted August 13 Welcome! Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted August 13 Share Posted August 13 Welcome to the forum, Joe! I'd agree with Gary, that those are classic symptoms of a faulty ground. We can try to help with the wiring, but it is one of the more challenging things to do over the internet. Link to comment Share on other sites More sharing options...
JW355714 Posted August 15 Author Share Posted August 15 Thanks Y’all! I cleaned up the left side, but it has t made a difference yet. Hopefully the right side is what’s bad Link to comment Share on other sites More sharing options...
Gary Lewis Posted August 15 Share Posted August 15 Thanks Y’all! I cleaned up the left side, but it has t made a difference yet. Hopefully the right side is what’s bad I'm hiding and watching. Let us know what you find. Link to comment Share on other sites More sharing options...
mat in tn Posted August 15 Share Posted August 15 I'm hiding and watching. Let us know what you find. I imagine one eye peeking through a keyhole:nabble_smiley_wink: Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted August 15 Share Posted August 15 I imagine one eye peeking through a keyhole:nabble_smiley_wink: 😶🌫️ Link to comment Share on other sites More sharing options...
JW355714 Posted August 15 Author Share Posted August 15 😶🌫️ Well, it didn’t work. Hopefully some attached pictures show what I had versus what I installed. Link to comment Share on other sites More sharing options...
Gary Lewis Posted August 16 Share Posted August 16 Well, it didn’t work. Hopefully some attached pictures show what I had versus what I installed.IMG_2554.jpeg Did you clean up where the ground goes against the radiator support? And it looks like there has been some re-painting. Is the ground still on the engine going to the cab near the windshield wiper? There's a grounding problem somewhere. For a test run a jumper from the ground on the battery to that ground lug in the picture and see if that helps. Link to comment Share on other sites More sharing options...
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