93 MH 613 tail light help needed.

[dennis101279]

I have a 93 MH 613 and I need to wire up the rear 2 tail lights and the back up light. I have 2 red 4 inch round and one clear 4 inch round. I have 4 wires back there, a red white black and green wires back there. I can't seen to figure them out.

Edited July 22, 2014 by dennis101279

[BC Mack]

if your lights are like mine... just posted some pics... the red lamp pops out of the rubber housing, the back casing of the lamp indicates the position of each wire (tail/turn/ground) so check the pigtail and match the colour... (red black white seems right??) whatever is left over should be reverse. all bets are off if it is "custom" then you have to dig out the test light and start probing..

BC Mack

[dennis101279]

You think this would be simple as that but I have either a turn signal or a bright brake light. Cant get it all to work. I have to be over looking something. The red white and black are hot. Red and white are the turn signals.

[BC Mack]

checked the electrical diagram...

main harness to rear junction plug..

green = back-up

white = left turn/brake

red = right turn/brake

black = tail/licence

so, the three 'hots' means brakes applied and tail lamps on... if red or white is flashing turn signal overules the brake.

the brake and turn are the same wire... so, red lamps not red/amber at rear

get good grounds to all the lamps or you will have more issues.

pre-wired lamps don't always match truck wire colours so check the lamp for info

caveat emptor... had a long day, hope this makes sense..

BC Mack

[dennis101279]

That's what I thought. I was sitting here thinking. I wonder if my brake light switch is stuck. That would explain why they are so bright.

[85snowdog]

I don't want to mess you up, and maybe you know this , but older Macks , when the key switch is on or truck is running the brake lights stay on when the park brakes are on. The lights only come off when the brakes are released.

Keith

[farmer52]

I don't want to mess you up, and maybe you know this , but older Macks , when the key switch is on or truck is running the brake lights stay on when the park brakes are on. The lights only come off when the brakes are released.

Keith

X2

[dennis101279]

Ok so I have been messing with this again. I wired them like I thought and the blinkers work but the 4 ways are dim. I turn the marker lights on and they are bright like the brakes are on and have no turn signals. I release the parking brakes and the same thing. I am stumped.

[farmer52]

Sounds like a ground issue. The MH fiberglas cabs are notorious for having ground issues. Check the main cab ground.

[Marcel67]

Ok on my mh same year the brake lights are on when you are low on air pressure. The minute the pressure is up the brake lights turn off. I don't know if that is original but all works fine

[39 Baby Mack]

Ok on my mh same year the brake lights are on when you are low on air pressure. The minute the pressure is up the brake lights turn off. I don't know if that is original but all works fine

That's the way our '93's were wired up too.

The '85's and '87's were wired up through a parking brake switch.

I changed the '93's over to work the same way the older ones worked.

Don't remember how, was to many years ago!

Ron

[Marcel67]

That's the way our '93's were wired up too.

The '85's and '87's were wired up through a parking brake switch.

I changed the '93's over to work the same way the older ones worked.

Don't remember how, was to many years ago!

Ron

Ron I have the wire diagram in my parts book, would that help Dennis?

[39 Baby Mack]

Probably, it sure couldn't hurt!

He should have one on the back of the access panel to the circuit breakers and relays.

You should have one there too!

Ron

[Marcel67]

Will check mine tomorrow

[dennis101279]

Mine doesn't have it on the panel but yea that would help. Plus my radio now keeps going on and off. I think I have a ground issue some place but every thing else is fine.

[Marcel67]

Ok Dennis let me scan the diagram for you and posted here

[MHfred]

Sounds like a ground issue. The MH fiberglas cabs are notorious for having ground issues. Check the main cab ground.

Ken, where is the main cab ground?

[dennis101279]

Well I got every thing to work as long as the marker / headlights are off. If I turn them on they come on bright as if the brakes are on. I started released the brakes put it gear and nothing. Only bright red brake lights. Now I noticed my radio is going on and off if the truck is running. I hate wiring. I am sure its something simple. Just finding it sucks.

[farmer52]

Well I got every thing to work as long as the marker / headlights are off. If I turn them on they come on bright as if the brakes are on. I started released the brakes put it gear and nothing. Only bright red brake lights. Now I noticed my radio is going on and off if the truck is running. I hate wiring. I am sure its something simple. Just finding it sucks.

Definitely sounds like a dash ground issue. I believe MHfred stated the dash ground is behind the speedo/tach. Also check the ground for the switch panel.

I had an issue when I turned on the headlights the fuel gauge would go to "E". I run a ground wire from the gauge to a panel screw. Also had an issue of no headlights. Found a loose connector on the dimmer switch.

[MHfred]

My problem on my 89 was instruments not funchioning preoperly. Attached is a picture with the speedo and tach removed. There are connectors that slide onto the ends of circuit boards which you can see sticking out on the left side of the picture. I cleaned the contacts with contact cleaner and Q tips. It tookcare of my dash grounding problems.

The other day I replaced my alternator and cleaned a ground to the frame rail which is in behind the left (driver side) front wheel. It had 3 wires on it but I don't know what they grounded.

[dennis101279]

Thanks for the help. Mine has 2 wires on the frame there in the front another behinnd the fuel tand and the one on the rear. I am going to redo the grounds on the front today and open the dash to see what i find. This is just driving me nuts that i can figure out simple lights and a radio.

[dennis101279]

Got her fixed. I was the cab ground. I found a wire that goes to the tranny for the back up light and was broke. Now all the lights work. Now to fix the radio. lol.

[farmer52]

Fred,

Can't "quote" or "copy and paste" with WIN8.1. But to answer your question "where is the main cab ground"....

Looking at the MH electrical manual (8-505), the cab/chassis ground runs thru the main wiring harness. The junction box/chassis ground cable is located behind the LH (driver's side) headlamp. There is a multi-pin (21 pole) connector and what looks like a separate wire. Not sure if the chassis ground runs thru the connector or it is the separate wire. I am in OH and not at the MH so I cannot be more explicit. I suspect there is a connection to the frame on the LH side.

Maybe the "all knowing" (this is a compliment) 39 Baby Mack Ron can be of more help.

Upon further review, the separate wire loom has the chassis ground. There are four wires that run from the circuit breaker box (2-ammeter shunt, master circuit breaker, and starter relay). The chassis ground is along this group of wires. The ground wire is identified as 6B (6 gauge black?). I am no electrician so I hope this makes sense.

It is shown on the CAB WIRING HARNESS skizmatic (page 21 in my book). Flip open the page and it is in the lower left corner next to the 21-pin connector (MAIN CAB TO ENGINE CONNECTION.

[dennis101279]

My main cab ground is on the left side just behind the cab pin on the frame. After looking in my dash they all run to a ground on the steering collum that runs to that ground. It all works good as new now.