Looking for electrical help (1 Viewer)

[badsamaritan]

Been chasing an issue with the 40 for a long time and no luck. Basically the heater fuse blows but only after a long drive. I've thrown more time and money at this than I care to admit and can't go for a drive around the block without that fuse blowing. Food, beer, whatever if you can take a look at it and see what I'm missing. I'd offer to drive it to someone but until I get a new steering box it's really not safe on the freeway

 

[BreckenridgeCruiser]

1972 right? Oem harness or been replaced?

 

[elripster]

Does the fuse look cooked?

 

[Bud_Dude]

I'd be happy to help you troubleshoot the problem, but know nothing about the 40s at all.
Do you have an accurate wiring diagram for your 40 that you can share?

 

[BreckenridgeCruiser]

Do you have an accurate wiring diagram for your 40 that you can share?

That's why I was asking the year and if oem harness. I have the diagram for a 1972 and thought we could unplug each system on that circuit until we found which was blowing the fuse...

 

[elripster]

So a few things. If the fuse will run for some time each time before blowing you don't have a dead short at least at startup. You could have an intermittent dead short though which will be fun to track down. However, it would be good to know if the fuse looks melted of overheated. That would indicate the connections between the fuse terminals and fuse are dirty or not making good contact. If the fuse looks good and just blows after a few hours, I might ask if the fan motor has been replaced? If not, it's bearings could be old/dried up grease, and it could be pulling too much current which fatigues the fuse.

 

[elripster]

If you have a meter that can measure the current we can look up the fuse blow curve and pretty quickly see if you have a sustained load condition or not. If so, replace fan motor, if not, it's likely an intermittent short which is probably a chaffed harness at some point and will require chasing down the schematic looking for chaffing points.

Dumb question but is there a chance anything has been tap-spliced into that circuit at some point?

Frank

 

[badsamaritan]

Hey guys, thanks for all the replies and the help, I think I figured out the problem, then went to Nor-Cal for 10 days and I didnt get a chance to respond.

Long story short, I think it was a combination of several things, and not having a good diagram was really confusing the hell out of me. The laminated ones from Ebay are junk, and the ones here on Mud are from Haynes/Chiltons manuals and are better, but not great. In the end, I forked out the cash for a FSM off of Ebay and was able to run it down in a couple of evenings of testing.

Harness is a fresh reman from coolerman, so no ghetto splices or anything like that. Fuse Panel is brand new. I had also unplugged just about everything on the heater fuse circuit. I didn't know the parking brake switch and "brakes" dash warning light were on that circuit until I got the FSM. The parking brake switch was shorting internally and at one point got hot enough to burn my hand. I replaced it and the ground to the warning light housing and so far so good.

Voltage Regulator chassis is the main ground for the lights, and it also wasnt getting a good ground on my crusty firewall, so I made a new ground and ran it to the steering gear pedestal. That seemed to fix a few of the weird issues as well.

The gauges I took apart and cleaned the pcb with isopropyl alcohol and contact cleaner. Then I replaced all the rusty nuts and washers. That fixed the weird turn signal issue I had. I also replaced the ground wire that goes to the cluster. I've been on two long test drives and so far so good, no more blown fuses so fingers crossed I am on the right track. I'm going to one by one add in things on that circuit such as the backup lights and go from there.

 

[Bud_Dude]

Excellent job on the troubleshooting and sleuthing!
Bad grounds in cars are the source of many a problem. Many assume that any piece of metal on a vehicle is good to carry current back to the battery with low resistance... As you've seen, this is not always the case. Often the best thing to do is run new dedicated wires (of appropriate gauge for the current requirement) to a known good ground bus or bar rather than relying on the chassis to carry that current.

 

[elripster]

Excellent!

 

[badsamaritan]

Excellent job on the troubleshooting and sleuthing!
Bad grounds in cars are the source of many a problem. Many assume that any piece of metal on a vehicle is good to carry current back to the battery with low resistance... As you've seen, this is not always the case. Often the best thing to do is run new dedicated wires (of appropriate gauge for the current requirement) to a known good ground bus or bar rather than relying on the chassis to carry that current.

I picked up a junction block that I plan on connecting to the battery negative and then running grounds to it so they aren't tied to the chassis anymore. It will take me a bit to get that implemented but should help.