The repair order already split them. The books should be willing to repeat what the ticket said.
A ticket has parts, labor, sometimes a sublet to another shop, sometimes a core charge on a rebuildable part, and sometimes a shop-supplies line. If all of that lands in one income account, you cannot tell whether the labor rate is the problem or the parts margin is. The shelf in the back has the same disease as any other inventory: parts you have not put on a car are still yours. A core charge is stranger and more specific. It is often a deposit you pay the vendor and get back when you return the old part. It is not a cost until you fail to return the core, and it is not income when the vendor sends the deposit back.
When you enter the repair order, keep parts income and labor income apart, and keep parts cost on that job. A canned 'sales' total that adds them back together for the customer's invoice is fine. The customer can see one balance due. You need the split. Labor cost is the technician's time. Parts cost is the part that went on the car. If the technician is paid a rate that depends on billed hours, those billed hours have to be findable too, or payroll and the ticket will argue every Friday.
Discounts and warranties should stay on the ticket they belong to. A comeback that you perform for no charge is not zero. It is labor and parts you gave back. If you do not record it, the original job looks more profitable than the customer experienced, and the comeback week looks mysteriously expensive with no sale attached.
You sent the transmission, the glass, or the alignment somewhere else. That shop bills you. You bill the customer. Those are two amounts. Your margin on sublet is the difference, and it can be thin or backwards. Netting them into one line, or burying the sublet bill in parts, makes a job look like your labor when a specialist did the work. Keep the sublet bill and the customer charge both visible, on that repair order.
Sales tax, if it applies to parts and not to labor, or the other way around in your state, needs the same split. This page will not tell you your state's rule. Your tax preparer will. The ticket has to show parts and labor separately or the preparer is guessing from a single number, which is how tax gets overpaid or underpaid in a pattern you cannot see.
A core is the old part the vendor wants back. You often pay a core charge with the new part and receive a credit when the old one is returned. Until you return it, the core charge is something you are owed or something you are holding, not an expense to forget and not income when it comes back. If you expense the core when you buy and then record the credit as income, you create a fake cost and a fake sale. If you never track it, unreturned cores are cash you quietly donated to the vendor. A short list of open cores, by vendor, is the whole control.
Parts on the shelf follow the ordinary inventory rule. The parts-store statement is a purchase. The repair order is what moves the part to cost. Expensing the statement and also costing the part on the ticket counts the part twice. Expensing the statement and never costing the ticket makes every job look like pure labor. Pick the ticket as the moment of cost, and let the shelf hold what has not been installed.
Shop supplies billed to the customer as a fee are not the same as the supplies you bought. The fee is a sale, small as it is. The rags, hardware, and chemicals you bought are a cost, and some of them are still on the shelf. Do not net the fee against the purchases so the line goes to zero. Zero looks tidy and tells you nothing about whether the fee covers the purchases.
Send a week of repair orders, the parts-store statement, the bank account, and any core credits you can find. The first product is that week with parts, labor, sublet, and cores in separate places, the bank matching the deposits net of card fees, and a list of cores still open. You can then see whether the shop makes money on labor, on parts, or on neither. That is the question the single sales account was built to avoid, and it is the question the shop actually has.
Because you will not know whether to fix the labor rate, the parts markup, or the sublet habit. The customer's total can still be one number. Your books need the pieces the ticket already had.
Money tied to returning the old part. It comes back as a credit when you return the core. It is not income, and it is not an expense unless you keep the core and forfeit the credit.
When a repair order installs it. The parts-store bill only puts it on your shelf. Costing it at purchase and again on the ticket counts it twice.
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