M880 electrical questions

[Dave_1972]

I am finishing up new wiring harness install and running into problems at the rear of the truck. So a couple of questions.

First, did the M880's have an engine ground strap originally or should they have one?

Second, how do the rear tail light/brake lights ground? Is it through the metal tail light housing and then through the bed of the truck?

Here is what I am seeing:

Yesterday the right rear flasher/hazard/tail light worked but when you hit the brake that entire light went dark - IE no tail light no nothing.

So I cleaned up the screws mounting the housing and wire wheeled the housing where the screws go through and the bed where the screws attach.

And everything worked both Left and Right.

Did a little rattle-canning on the truck, reinstalled the grill, cleaned up the new carpet I installed, etc.

About an hour later I am closing up the shop and tested the rears one more time... now the LEFT brake is doing what the right one was before.

I am thinking of taking some left over ten gauge and making a frame-body ground at the cab (to make sure the frame has a good path to ground) and then another frame-bed ground.

Another weird thing. When I have the housing out of the truck sitting on the concrete with the wires still attached. The tail lights work. That doesn't make sense to me unless it is somehow working back to ground through the headlight/stoplight/turn signal switches.

One more thing - Reverse lights have never worked and I have been suspecting the Neutral safety switch, but maybe it's related.

Anyone got any bright ideas?

 

[Bob H]

I'm no electrician.
But when there is a weak ground on the M880's wierd things happen,
and not nessessarily with the light closest to the bad ground.

 

[goodbrewing]

Sounds like a bad ground to me. There should be a connection from the battery to the body. One from the motor to the body would do the same thing if your battery negative bolts to the motor like all mine do.
Good Luck

 

[Dave_1972]

In case anyone is curious - adding the ground cables for the cab-frame and frame-bed took care of the issue. I had already cleaned up and ran new wire for the engine and body grounds off the battery. In fact I had cleaned and rewired every ground on the truck. The problem I surmise was rusty body mounts making a poor connection between the bed of the truck and the path to ground through the frame back to the battery.

After 5 weeks and 150+ man hours the truck went for it's first test drive this afternoon and has only two remaining issues. One is an aftermarket electrical device I need to take a second look at. The other is that I have no reverse lights - I suspect I need to replace the neutral safety switch or drop the transmission pan and take a look at what is happening when reverse is engaged. Both issues I am confident I will work out - just not this week.

 

[lacoda56]

Just goes to prove, "You can never have too many ground straps"! Ok, I just made that up, but it sounded good.

 

[N1265]

Here is the deal with the lights on these things,

Yes the rear lights ground threw the metal housing to the bed of the truck, HOWEVER it is able to do this ONLY if there is a good connection from the actual light socket itself to the metal housing....

Remember, these sockets are pressed into the metal housing and will corrode at that point of contact. before making a trip under the truck ( and if you have any more grounding issues with the tail lights ) try this:

Take a pair of plyiers and grab the back side of the socket (where the wires are) and twist the socket inside the metal housing, this with a shot of WD-40 will re-establish the ground between the actual light socket and the metal housing... Also, be sure to checked the fuse in the glove box for the backup lights, it will be the fuse on the bottom row, all the way to the right.


Altho you may have to replace the reverse light switch I highly doubt you will have to pull the pan to fix the reverse lights. ( I think it just screws in )

Let us know how you make out .

 

[Dave_1972]

The factory fuse panel is gone - I have completely rewired the truck so it now uses the Painless fuse panel. I was concerned about the sockets and my next step was probably to rebuild them by installing new posts. I had already tried cleaning them up.

I tried the test listed in the manual for the neutral safety switch and it appeared to be ok. But I wonder if the switch is being actuated properly by the rooster comb. I know at the shifter there is an awful lot of play when engaging reverse. If nothing else I'd like to get a better feel for how the neutral safety switch works when the shifter linkage is moving into reverse.

At any rate I have an annual camping trip coming up in a week and half with a group of friends who have known each other since school. I think this will be something like our fifteenth year. I'll probably wait until after that to dig very deep into the reverse light issue. Especially since I want to spend some time replacing gaskets/fluids and greasing everything before I leave for camp.

Thanks for all the replies folks.