Power wires to glow plug controller get VERY hot, new controller and wiring harness

OLDBULL8

Good Morning Ya'll.
Supporting Member
Joined
Feb 12, 2009
Posts
9,923
Reaction score
338
Location
Delphos , Ohio
Here is Chrysler fusible link color codes, Ford is the same.
Just to add a little more from what rib245 noted above.
Black 12 AWG for 8 AWG wiring
Red 14 AWG for 10 AWG
Dark Blue 16 AWG for 12 AWG
Yellow/Tan 16 AWG for 12 AWG
Gray 18 AWG for 14 AWG
Orange 20 AWG for 16 AWG
White 22 AWG for 18 AWG

I posted, maybe a yr. ago showing the current pull of one glow plug. I no longer have that since my puter crashed. One GP will pull ~25 amps ><, 8 GP's will pull ~180 ><. The zig zag metal strip off the GP relay, (which is what the GP harness is connected to) is a Chromolox heat strip, it's there to control the rush current to the GP's. Now, the high current lasts about 2-3 seconds, then slowly decreases to ~5 amps >< depending on how long the GP cycle lasts. The Chromolox strip acts as a variable resistor, as it heats up, resistance goes higher. The GP controller is timed for a max of ~15 seconds. The early 6.9 controller acts/is totally different. Since rib245 posted his background, I'll post mine. Present age almost 85.

Ford Mtr.Co Lima Engine Plt.
1957 - 1964 Journeyman Electrician-Electronics
1964 - 1967 Foreman Central Maint. Electrical/Electronics/Hydraulics
1967 - 1987 General Foreman Maintenance Plant wide.
 

OLDBULL8

Good Morning Ya'll.
Supporting Member
Joined
Feb 12, 2009
Posts
9,923
Reaction score
338
Location
Delphos , Ohio
The automotive OEM's definitely do not follow the NEC code for residential and commercial applications. Normal code in most residential applications requires a 12 gauge wire for most 20 amp circuits. It can get complicated with derating for ambient temperatures, the number of conductors, etc. But 12 guage for 20 amps is the general application.

Most of these trucks have anywhere from a 75-100 amp alternator, and Ford never used anything bigger than a 10 gauge wire originally. It is a short run, and as you said there is a time or duty cycle helping the situation out also. I guess they felt generous and put two parallel 10 gauge wires to feed the glowplug circuit, but someone mentioned these wires carry over 100 amps when the glowplugs are working, and they are correct, a 40 amp would not hold it for a second.

If Ford can cut down on the copper being used and save a dollar on each truck, with the millions of trucks they built it adds up.
There are no fusible links used any where in Residential or Commercial wiring.
We are not dealing with 120VAC, we are dealing with 12VDC, As far as the alternator output is concerened, it doesn't enter in the equation at hand at all, alternators only charge the batteries to replace the current (wattage) drawn, the alternator voltage doesn't/shouldn't exceed 14.5 VDC. OHMS LAW.

To add to my previouse post, the fusible link(s) are mostly only 10" in length.
 
Last edited:

crewchief219

Full Access Member
Joined
Jun 21, 2013
Posts
95
Reaction score
0
Location
Wichita, KS
Wow thanks for sharing all of this info. I'm finding some inline 250 amp fuses that are pretty cheap and easy to replace. It sounds like the right rating for the system. Any reason these wouldnt work as well as a fusible link?
 

franklin2

Full Access Member
Joined
Feb 24, 2009
Posts
5,160
Reaction score
1,384
Location
Va
There are no fusible links used any where in Residential or Commercial wiring.
We are not dealing with 120VAC, we are dealing with 12VDC, As far as the alternator output is concerened, it doesn't enter in the equation at hand at all, alternators only charge the batteries to replace the current (wattage) drawn, the alternator voltage doesn't/shouldn't exceed 14.5 VDC. OHMS LAW.

To add to my previouse post, the fusible link(s) are mostly only 10" in length.

Current is current, no matter what voltage you are running at. Actually if you want to enter into ohms law, if your truck was using the max amount from the alternator(battery is dead, and all the accessories are on) lets say we are using 75 amps. Let's also say we have .01 ohms resistance through the 10 gauge alternator wire. That means 75x.01=.75v being dropped across the 10 gauge wire. .75v x 75a = 56watts of power being dissipated by the wire as heat. Notice the overall system voltage never enters any of these equations.
12v would actually be hurt more by this undersized wire than 120v. .75v/12v=6% drop in voltage in a 12v system while .75v/120v=.6% drop in voltage.
 

Latest posts

Forum statistics

Threads
91,217
Posts
1,128,469
Members
24,043
Latest member
tottripp

Members online

Top