amberwood

Name: Mack R688 (1990)

Date Added: 14 August 2009 - 05:07 PM

Owner: amberwood

Short Description: R series logger, works with 40' self loading rigid log skel

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Not a complete solution but I carry a hose with a trailer service fitting one one end a has a glad hand on the other to fill the start tank. Then you just need another truck to fill you up. So far I have not needed it, fingers crossed.

DTR

solved it. 20A glass fuse hidden on the back of the flasher can. looked ok but tested as blown. 20yrs of accumulated dust had it camoflaged as another bundle of wire. cause. LH rear lights on the prime mover, the loom was crushed between the new (6 weeks old) pintle towbar hanger and the chassis. A few thousand km's of vibration and it had worn through the insulation.

DTR

Picked up a load of logs early this morning, droppped in at home for a few hours for breakfast on the way thru, went back and i have no indicators.

I cannot to locate an allocated fuse or circuit breaker, no juice at the switch, so it is somewhere back from there in the system.

1990 R688 Valueliner,E7-400.

help

DTR

I have full color copies of a mid 80's Mack conventional wiring diagram. Send $10 and a SASE to POB 97784, Raleigh, NC 27624.

OK, all fixed. It appears that there was a loose wire on the throttle microswitch. thank all for the help

DTR

Keep in mind there are many components to make the system work. There is the switch in the dash, the switch on the clutch pedal, the fuel pedal, sometimes a speed sensor in the system, and of course the switch in/on the injection pump or linkage. Most any of these can fail internally from use and cause a short to ground. By you mentioning that the fuse does not blow until you go to use the engine brake is the first "clue" the the system is giving.

Does the fuse blow if you select the engine brake on while the truck is not moving? How about if the engine is not started, and the engine brake is selected? This can rule out about 1/2 of the system right off if the fuse does not blow. I would start the engine, run it at about 1800 rpm, select engine brake, get off the throttle and let the engine come back to idle, then "rev" the engine up and down a few times and then check the fuse again. The speed sensor portion of the system should be alright if the fuse holds doing this as the brake should not work unless the truck is going a few mph.

Rob

Rob. The fuse does not blow until the exhaust brake is activated, and actually it is the second application that the fuse fails on. It appears that a previous owner has fitted a 10A spade fuse directly behind the dash switch, this might be a reoccuring issue. Answering some of the other queries raise, yes it is a late mechanical engine, all clockwork and relays. i am bring the truck back to the yard tomorrow to repair the crane and will get the mutimeter out to check the potential problem switches.

thanks

DTR

Chances are that you have a shorted solenoid, or a pinched, cut/chaffed wire in the harness. If it were mine the first thing to do would be to unplug both cylinder heads from the harness and drive the truck. If it still blows the fuse, the solenoids and/or associated wiring to the heads can be eliminated for now. If the fuse holds, then plug only one cylinder head back in and drive the truck again. If the fuse still holds, unplug the one cylinder head, and plug the other one in. Drive the truck again and discern if the fuse still blows. If it still blows I would unplug, or unfasten the wiring harness from the switch in the dash that enables the system and see if the fuse holds. If the fuse now holds, get the multimeter out and "ring out" the wiring to find a direct short to ground by reading the meter, and following the wiring, (by hand most times) to find the problem.

By doing these functions you are isolating where the problem lies.

Rob

thanks rob. i will give it a go first chance and see where the problem lies.

DTR

DTR,

I would suggest that you look around this site, or go online to E-Bay

to find and purchase a Service Manual for the R688 right away.

It's a practice I have used for years for all of my vehicles,

and it has served me pretty well.

Reprints and original manuals in all conditions are readily available for most later Macks,

and are pretty reasonably priced.

I know my early Mack R model Service Manual has wiring diagrams.

I'm just curious - how are you going to use the truck?

Paul Van Scott

I have a specialty sawmilling business, and the mack is set up with PTO etc to tow a 40' rigid log skel with a midmount Loglift crane.

I try to check ebay regulary but no luck on the right manual as yet.

DTR

Just joined up having recently purchasing my first semi. The first gremlin has just turned up in the electrical system. The 10A fuse on the engine brake pops after a single application. I was hoping to source a wiring diagram, or even better tap into someone who has seen this problem before.

DTR