It would be much easier and reliable to just plug in the whole harness. You will have to take the cluster out, and possibly the heater section, but it's all a unbolt, plug in deal. No soldering and insulating, which you should do if you want a reliable splice.

 

The wiring harness is mostly in, now I need some help understanding what's what.


The pic is my understanding of the wiring diagram I received earlier. It appears to me that there are two relays, one for the starter and one for the glow plug system. Is this correct?


This is the glow plug relay I bought yesterday. Which side is the ground and which side does the purple wire go on, also, which side does the battery hook up to and then where do the other wires with the fusable links go? is there a wire that should go from the glow plug relay to the starter relay?



These are the wires I have yet to hook up. Does the metal cylinder resting on the battery get grounded to the fender? My positive battery cables have a 4ga? wire that is longer than it seems to need to be, and there is a 10ga? black wire that runs from/to the starter solenoid. The light green fusible link comes from the alternater harness. the orange wire at the bottom of the pic is t-tapped into the green and red wire from the voltage regulator (metal box with motorcraft on it).


There's also a white and red wire in the glow plug harness that I can't find a connection for. it also doesn't appear on the wiring diagram. wiskey tango foxtrot!

 

Dave was there midyear change to the wiring on 87's.
Mine has the new style glow plugs.
The fuel heater is inline before the filter. There are no sensors on the filter.
The water seperator is mounted on the firewall under the brake booster.
This truck is an 87 with a 6.9L and a ZF 5 speed. The tag on the trans is dated 86. Actual production year?

This truck also has (dealer installed) A/C and is a nightmare to find parts for. I used parts for a 90 and had to have custom hoses made to get the right fittings where I needed them.

 

chris1066, I don't understand your post. it looks like you are responding to a different post.

 

Didn't mean to cofuse you. Earlier in this post Dave S mentioned some changes that took place in 87. My truck is an 87 and the engine harness is very similar to yours. I was wondering if the change was midyear.

Since the relay is not marked it should not matter which side is ground and which is power. Your just hooking to a coil of wire to act as a magnet. The battery side and the glow plug side also do not matter as you are just connecting them when the relay is energized. Looking at the diagram on page one of this post you should have two wires with fuse links coming off one of the big terminals on the relay and going to the glow plugs. The other terminal is battery power.

Do you have the wires to the fast idle, cold start advance and Fuel shut off solenoid hooked up. If I rember right I thought those wires were red and white. I would have to look at mine to make sure.

 

Is everybody (including moderators) afraid of this thread or do you just not care? I'm in need of help. If you need more pics, I'll post more. If you need more description, I'll post more. Right now I'm cross-eyed from looking at diagrams and I can't think straight. This forum helps me to think and I get a lot of great help and ideas from it, but only if I get some feedback.

I know there are other pics on this website of GP wiring, relays, under-hood shots; but the gallery is WORTHLESS to search through because all i can search is make, model, year, drive, mods. Technical galleries don't appear in the lists, can't search for them, WTF? If this thread is BS then I wish a moderator would pull it from the list so I wouldn't have to wait for nothing to happen.

 

Dieselutheran21,
Sorry, I had family dutys this weekend and a day job plus.
And right now it is pouring down the snow outside after I just finished eating, so I am probably looking at a 4 AM call to plow snow.
As for the not care statement, that kind of hit me wrong tonight.
Everyone on this forum is here because they care and want to share their knowledge.
I am not paid to do this, I am 3000 miles from you and am sitting here typing this reply when I should be sleeping since I probably have to go to work in three hours.
Don't tell me I don't care.
Since that is off my chest, I will answer as much as I can off the top of my head.

Battery 4 AWG to glow plug solenoid, one of the larger termianals, makes no difference which.

Now we need a jumper off that terminal to the front large terminal of the starter relay.

The other large terminal of the glow plug relay should have a black with pink stripe small AWG wire (wait to start light) and two large AWG wires orange with white or green stripe.
May be one of each.


There will be a couple more wires to attach to the battery terminal of the starter relay at a later time, that terminal was used as a power distribution point.

Black 10 AWG wire to starter hooks to the other large terminal of the starter relay.

Small terminal of the starter relay should have a blue wire with a red stripe on it.

I have a black ground wire that starts at the negative terminal of the battery then jumps to the mounting srew for the starter relay then jumps to the mounting screw for the voltage regulator and then jumps to the small ground terminal on the glow plug relay, usually the one closest to the fender although it makes no difference.

White wire red stripe......can't remember right now.
There are two wires, one is red with white stripe the other is white with red stripe.
One goes to the oil pressure sending unit at the center rear of the engine.
The other goes to the coolant temp sender on the drivers side front of the engine.
Look at both of the sensors, see which is where.



The purple controller wire goes on the other small terminal of the glow plug relay.

And now I am off to bed, sorry there are 16 posts I did not even get to look at tonight.

 

Dave, thanx for the reply. My dad is a heavy equip operator for the WY DOT and I sypathize with the 4AM snow plow duty. The statment about caring was a meausred statement that was a risk of making people mad in order to get a response. While not an excuse for waving the red flag in people's faces, It was nearly midnight after unsuccessfully working on my truck for 5 frustrating hours.

I now know more than I did before, like the mystery wire on my GP harness goes to the oil pressure sender, that I need a ground wire to the starter relay, voltage regulator, and the GP relay. Does that mean you have discontinued using the black wire with the 90deg boot for neg to the GP relay? Thank you again.

 

White wire red stripe does go to the oil pressure sender.

Red with blue stripe is the wire that should go to the starter relay, I had it backwards last night.

I am still using the stock grounding loop which ends with the angle plug on the glow plug relay.
The stock ground wire runs to all those places, it just has a couple male/female splice connectors between all the end connections.

The metal cylinder is a radio noise capacitor, the housing should mount on the regulator hold down screw that the ground wire is on.
The wire that comes out of the capacitor goes to the A terminal of the regulator connector.

The other wires that go on the battery terminal of the starter relay have fusible links on the end that attaches to the relay.
One link goes to a yellow 14 AWG that puts power in the cab if I remember right.
The other link ends with a 8 AWG that goes to the alternator output terminal and a small yellow wire maybe 18 AWG that also goes into the alternator harness.

Without walking up to my truck, I am wondering if the glow plug relay has been replaced with a starter relay.
I never paid that much attention, but I think both my small terminals are the same size.

After I read through the rest of the posts, I will walk up and look.

I should not have jumped at you last night, but I started going through the posts earlier in the evening.
Then I get a call that one of our plow trucks needs a new fuel pump it won't run right.
So out the door, fix the truck (Dodge gasser) with a new fuel pump and line filters.
Walk back in the house at midnight to eat and finish going through the posts.
I think yours was the third one I read and answered.

Sometimes I wonder why I do this position, 2 or 3 hours every day.
That adds up to a lot of time by the end of the year.

 

Success! Kinda. Thanx again Dave for your help. I moved the two fusable link wires to the power side of the GP relay, made a ground wire that runs from the - post on the battery to the starter relay, and from there to the voltage regulator and grounded the capacator to it. When I turned the key, ta-da, a proper glow plug power cycle. I verified this by hooking my multi-meter up to the GP connections and watched (with no small amount of satisfaction) as the multi-meter registered 12v for a couple seconds, then dropped off, then back on quickly, off, on...you get the idea. I think the glow plugs might actually work now.

Now to the "kinda" part. The ignition switch wire does not make the starter relay kick on. When I turn the key, it registers 6v, and when I turn the key to the start position it drops to 0.25v. Wha? It looks like the red/lt blue wire runs all the way back to the ignition switch connection on the steering column. Does that mean that the ignition switch is bad. I couldn't find any burned fuses in the fuse block. I made a jumper wire and touched the power feed to the s post on the starter relay, and the starter engaged and turned the truck over.

I see in the wiring diagram that the ignition wire connects with the neutral safety switch. Could that be the problem? there are some wires that come from the side of the transmission that have their sheathing (sp?) rubbed off by the front driveshaft. Any other suggestions about the faulty ignition switch wire (red/lt blue)? Also, what tank does the tank selector solenoid default (no power) to, front or back? thanx

 

oh, Dave, I hope the reason you "do this" is because there are those of us who can't. I hope it helps to hear that you have helped me when no one else did. Thank you again.

 

Sorry it took so long to get back to you, flu for a nice way to spend Friday and Saturday.

The start wire does indeed go through the neutral safety switch and a clutch interlock switch between the ignition switch and the starter relay.
On trucks with a manual, there is a jumper across the connector for the neutral saftey switch, and on trucks with an automatic the clutch interlock connector is jumpered.

Unfortunately the ignition switch or any of the wires or connectors between the switch and the relay could be where the problem is located.
I would start at the ignition switch with a voltage test and work toward the starter relay to find the problem.

The tank will stay on what ever tank is selected until power is applied to the selector valve telling it to change.

Thanks for the kind words, it does help to here that we can make it better for someone with a problem.
At one time, everyone in this forum was at the place you are now, some of us had others to help us through the problems so know we are returning the favor.

 

This sucks. I'm only able to work on my truck once a week, and it is a 67 mile round trip to do so. I got to my truck today to run a compression test and found my batteries dead, 1.2v still in them. I made sure the headlights were off when I left the truck. What else would cause the batteries to run down? I do not have the wires hooked up that control the dome-light when the doors are open, could that make them constant on? I'm wondering if there is any connection to the ignition ground/short?

 

Sent an email....... FYI there is a place on the drivers side under the booster where wire sheathing can retract and the wires will short out.......check for that on one of the large grey connectors........ I will email pics after you get back to my email.

FYI....... unhook all batteries when finished working on it.

 

A bad diode in the alternator will also kill the batteries.