Bolt size for ground strap from firewall to passenger side cylinder head

[BigMAC22]

I'm trying to figure out why the fuse for my dash lights keeps blowing. This is on an '82 with a 305 engine. I've been tracing wires and looking for grounds and I noticed in the engine bay a ground strap from the firewall that has one end just hanging loose. I read a post that says this end is supposed to attach to the passenger side cylinder head, sure enough, there is a hole back there just below the passenger side valve cover but it is missing the bolt. Does anybody know what size bolt fits in there? Or can I just get a longer braided wire and ground it to the frame instead?

[rich weyand]

It's probably a 3/8-16.  It's the same size as the same hole on the other head, which is where the power steering pump bracket is bolted.  But you can just connect that strap to the outer rear valve cover bolt.

The engine is what brings all the grounds together: battery, cab, and frame.  So connecting it to the frame isn't as good.  BTW, you do have the other ground strap on the front of the engine to the driver's side frame rail, right?

[BigMAC22]

Ok, thanks, I will pick one of those up then.

I didn't see that front strap but I will look a little more today after work and see if I can't find it.

[pholliday1]

(while there can be many)  A very common cause to your dash light blowing is when radio modifications have been made and the wire that comes over from the headlight switch isn't used or "covered up" and it grounds out causing a short. When your dash light fuse blow are your tail lights blown also?

[BigMAC22]

When I bought the truck the radio was missing so I put in a new head unit and taped off any unused wires. I will try pulling the head unit again and double check that the tape didn't fall off or something.

When the dash light fuse blows only the dash lights are out. All other lights are still functional. I checked the circuit board and each bulb but they looked good. Cleaned the contacts on the 18 or 16 pin connector that plugs into it but that didn't help. I replaced the fuse and then turned on one thing at a time and then back off to see if the fuse would pop. After trying several other things like turning on/off my radio, turn signals, etc I turned on my wipers and when I went to turn them off (slide the wiper control knob to the left several times) the fuse popped. Not sure if that was just coincidence or if it actually had something to do with it. I did take the delay module out of the dash a couple months ago to stop the random "phantom wipe" issue that I had but the dash lights just started going out about 2 weeks ago. As mentioned above, I still have to slide the wiper switch lever to the left to get the wipers to stop sometimes. Not sure if that could have something to do with it.

I'm curious to see what hooking up that ground strap to the cylinder will do.

[bd]

The dash light circuit uses gray wiring to feed the lamps.  Look for any gray wire that may be pinched or rubbing.  Don't forget to check the A/C control head and ash tray illumination wiring.  Some wiper switches have their own bulb, too.

[BigMAC22]

Thanks, bd, good to know. I think the ash tray illumination is via a fiber optic cable linked to the far right upper most dash bulb that mounts into a slot in the sheet metal just above the ash tray. Couldn't figure out what that was for a while because the illumination from it is extremely dull and not noticeable! I could only tell it was fiber optic once I pulled the cable and looked at the end of the wire and saw a slight glow! Anyways, I will check for gray wires.

[BigMAC22]

Update on the dash lights issue.  I was finally able to get to the ground location under the dash near the parking brake. The ground has 6 metal prongs of which 2 were occupied. One of them was loose so I cleaned the metal up and snapped the connectors back on the terminals. Dash lights have been working for about a week now, the longest they have in a while. Hopefully this is a permanent fix. Thanks for everyone's help.

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[rich weyand]

Excellent.  Thanks for the follow-up.

[BigMAC22]

Update: spoke too soon! Dash lights went out again this morning...boo. Not sure what else to do to fix this problem. Almost to the point of just running a new switch and throwing some bright white LEDs behind the cluster and be done with it. Lol

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[bd]

Was it the fuse again?

When you cleaned up the ground under the dash, did you unbolt the ground bus terminal strip from the cab sheetmetal?  Often times there is oxidation between the terminal strip and the cab.  If you didn't before, take it apart now and sand the metal for a good connection, then smear some anti-oxidant paste on the connections and reassemble. 

Intermittent connection problems can occur at the headlamp switch, as well.  The dimmer rheostat has a tendency to burn interrupting current flow to the dash lamps.

[BigMAC22]

I haven't had a chance to check the fuse since it happened on my way into work. I'm about to head home and will check.

I did unbolt the ground bus terminal strip and I scraped the metal behind where the strip was sitting with a screwdriver to get to clean, bare metal. I will try to get my hands back there to sand the area but it looks tight. Would almost like to replace the $15 headlamp switch too just to rule that out. Thanks bd.

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[BigMAC22]

Yep. Fuse is blown again.

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[bd]

Well, the circuit section between the 5-amp instrument lamp fuse, the cluster and the one or two standalone lamps is pretty simple.   

You could start by turning on the park lamps and watch behind the dash for any arcing or crackling as you "gently nudge and tug" the harness this way and that.  Of course, you could go through a lot of fuses doing that.  So, pick up a 5-amp auto reset circuit breaker and substitute that for the instrument lamp fuse.  Refer to the 1983 Wiring Manual (pages 9 & 10), take your time and be patient.  If push comes to shove you may need to remove some tape and trace the 'gray' wire.

Occasionally, wires chafe between the fuse block and the bulkhead connector.  To separate them, you'll need to remove the two mounting screws that fasten the assembly to the firewall, then release the two clips that lock the fuse block to the connector.

Remember to remove the 'test' breaker and install a fuse when your done.

[BigMAC22]

I know this post is kind of old but I think I may have fixed the issue with my instrument panel lights for good this time and just wanted to share. I took the ground terminal block under the dash back off and sanded the metal really good where the terminal bolts down to the cab, likewise with the back of the ground terminal to get good metal to metal contact. I could not tell until I sanded the metal just how much oxidation there really was! Put some dielectric grease between where I had sanded the cab and the ground terminal block and reassembled everything. I also went to do a little upgrade on my taillight housings (paint them white to reflect more light; turned out pretty neat ) and found a bulb that was coming loose from it's socket (but still functioning) and on the other side, a bulb that looked like the filament was messed up. So I just replaced all my tail light bulbs. The wiring for the passenger side taillight that grounds just below the taillight housing had paint on it so I unbolted it and sanded that down to bare metal as well. The instrument lights have yet to blow the fuse again so it seems like this has finally corrected the issue. Now on to the starting issue!